LOW BACK PAIN AND ASSOCIATED FACTORS IN ADOLESCENCE : A

D 1316

OULU 2015

UNIVERSITY OF OUL U P.O. Box 8000 FI-90014 UNIVERSITY OF OULU FINLA ND

U N I V E R S I TAT I S

University Lecturer Santeri Palviainen

Postdoctoral research fellow Sanna Taskila

Professor Olli Vuolteenaho

Paula Mikkonen

Professor Esa Hohtola

O U L U E N S I S

ACTA

A C TA

D 1316

ACTA

U N I V E R S I T AT I S O U L U E N S I S

Paula Mikkonen

MEDICA

LOW BACK PAIN AND ASSOCIATED FACTORS IN ADOLESCENCE A COHORT STUDY

University Lecturer Veli-Matti Ulvinen

Director Sinikka Eskelinen

Professor Jari Juga

University Lecturer Anu Soikkeli

Professor Olli Vuolteenaho

Publications Editor Kirsti Nurkkala ISBN 978-952-62-0951-7 (Paperback) ISBN 978-952-62-0952-4 (PDF) ISSN 0355-3221 (Print) ISSN 1796-2234 (Online)

UNIVERSITY OF OULU GRADUATE SCHOOL; UNIVERSITY OF OULU, FACULTY OF MEDICINE; MEDICAL RESEARCH CENTER OULU; OULU UNIVERSITY HOSPITAL

D

ACTA UNIVERSITATIS OULUENSIS

D Medica 1316

PAULA MIKKONEN

LOW BACK PAIN AND ASSOCIATED FACTORS IN ADOLESCENCE A cohort study

Academic dissertation to be presented with the assent of the Doctoral Training Committee of Health and Biosciences of the University of Oulu for public defence in the Auditorium of Kastelli Research Centre (Aapistie 1), on 20 November 2015, at 12 noon

U N I VE R S I T Y O F O U L U , O U L U 2 0 1 5

Copyright © 2015 Acta Univ. Oul. D 1316, 2015

Supervised by Professor Jaro Karppinen

Reviewed by Professor Anssi Auvinen Professor Charlotte Leboeuf-Yde

Opponent Docent Katri Laimi

ISBN 978-952-62-0951-7 (Paperback) ISBN 978-952-62-0952-4 (PDF) ISSN 0355-3221 (Printed) ISSN 1796-2234 (Online)

Cover Design Raimo Ahonen

JUVENES PRINT TAMPERE 2015

Mikkonen, Paula, Low back pain and associated factors in adolescence. A cohort study University of Oulu Graduate School; University of Oulu, Faculty of Medicine; Medical Research Center Oulu; Oulu University Hospital Acta Univ. Oul. D 1316, 2015 University of Oulu, P.O. Box 8000, FI-90014 University of Oulu, Finland

Abstract Low back pain (LBP) is a common condition already in adolescence and seems to predict future symptoms. Most of the previous longitudinal studies on LBP have been conducted in adult populations. Among adolescents, LBP has been linked most convincingly to psychosocial factors and smoking. We are not aware of any previous studies on clustering of potential risk factors in adolescent LBP. The main objective of this study was to analyze the potential associations of mainly modifiable psychosocial and lifestyle factors with LBP in adolescence. The factors evaluated were overweight, smoking, physical workload, family’s socioeconomic status, and the co-occurrence of psychosocial and lifestyle factors. The present study used the database of the 16- to 18-year-old adolescent subcohort, Oulu Back Study (n=1,987), of the Northern Finland Birth Cohort 1986. Moreover, we evaluated whether the associations differ depending on the presence of LBP symptoms at baseline of the two-year follow-up period. LBP was common among cohort adolescents as, on average, every second adolescent reported LBP, girls reporting more symptoms. As a whole, more associations were found among girls than boys. Overweight was associated with new LBP in the follow-up, but the association was not strong. Prolonged habitual smoking was associated with LBP, particularly with symptoms at baseline and follow-up. High exposure to awkward trunk postures and an overall physically demanding job were especially associated with new LBP in the follow-up. Family’s socioeconomic status was not consistently associated with LBP. At 16 years, four latent class clusters of psychosocial and lifestyle factors were found in both genders. Clusters characterized by behavioural problems were associated with LBP among both genders. Especially girls with the combination of emotional and behavioural problems were at the greatest risk of seeking care for new LBP. The results of this study indicate that LBP in adolescence is associated with both psychosocial and lifestyle factors. The information obtained may be utilized for improving preventive measures and individual care for adolescent LBP.

Keywords: adolescent, cohort studies, life style, low back pain, obesity, overweight, psychosocial factors, smoking, workload

Mikkonen, Paula, Alaselkäkipuun liittyvät tekijät nuoruudessa. Kohorttitutkimus Oulun yliopiston tutkijakoulu; Oulun yliopisto, Lääketieteellinen tiedekunta; Medical Research Center Oulu; Oulun yliopistollinen sairaala Acta Univ. Oul. D 1316, 2015 Oulun yliopisto, PL 8000, 90014 Oulun yliopisto

Tiivistelmä Alaselkäkipu on yleistä jo nuorilla, ja varhain koetut oireet ennustavat myöhempiä selkäkipuoireita. Suurin osa alaselkäkivun seurantatutkimuksista on tehty aikuisväestöllä. Nuorten alaselkäkivun on esitetty vakuuttavimmin liittyvän psykososiaalisiin ongelmiin ja tupakointiin. Alaselkäkipuun liittyvien tekijöiden mahdollista kasautumista ei ole nuorilla tutkittu aiemmin. Tämän väitöstutkimuksen tarkoituksena oli selvittää, ovatko pääasiassa muunneltavissa olevat psykososiaaliset ja elämäntapatekijät yhteydessä nuoruudessa esiintyvään alaselkäkipuun. Arvioitavina tekijöinä olivat ylipaino, tupakointi, fyysinen työkuormitus, sosioekonomiset tekijät, sekä psykososiaalisten ja elämäntapatekijöiden kasautuminen. Tutkimusaineisto koostui Pohjois-Suomen syntymäkohortti 1986:n osaotoksesta (Oulun selkätutkimus), johon kuului 1987 16–18-vuotiasta nuorta. Mahdollisia yhteyksiä arvioitiin erikseen sen mukaan, raportoivatko nuoret seurannan alussa alaselkäkipuoireita vai ei. Alaselkäkipu oli nuorilla yleistä, ja tytöillä yleisempää kuin pojilla. Keskimäärin joka toinen nuori raportoi oireita. Tutkittujen tekijöiden ja alaselkäkivun välisiä yhteyksiä todettiin selvemmin tytöillä. Ylipaino ennusti seurannassa ilmaantuvaa alaselkäkipua, mutta yhteys ei ollut vahva. Säännöllinen tupakointi oli yhteydessä alaselkäkipuun ja etenkin toistuviin oireisiin. Tutkituista työkuormitustekijöistä etenkin hankalat työasennot ja fyysisesti monella tapaa raskaaksi luokiteltava työ altistivat seurannassa uudelle alaselkäkivulle. Sosioekonomiset tekijät eivät olleet selkeästi yhteydessä alaselkäkipuun. Latenttien luokkien analyysi tunnisti seurannan alkuvaiheessa neljä erilaista ryhmää (klusteria) psykososiaalisten ja elämäntapatekijöiden perusteella molemmilla sukupuolilla. Sekä tytöillä että pojilla alaselkäkipua esiintyi erityisesti niissä ryhmissä, joissa esiintyi runsaasti käyttäytymishäiriöitä. Tunne-elämän ja käyttäytymisen ongelmat ennustivat alaselkäkivun vuoksi hoitoon hakeutumista tytöillä. Tulosten perusteella nuorten alaselkäkipuun liittyy sekä psykososiaalisia että elämäntapatekijöitä. Tuloksia voidaan hyödyntää alaselkäkivun ennaltaehkäisyn ja nuorten yksilöllisen hoidon suunnittelussa.

Asiasanat: alaselkäkipu, elämäntapa, kohorttitutkimus, psykososiaaliset tekijät, tupakointi, työkuormitus, ylipaino

lihavuus,

nuoret,

To my grandchildren

Acknowledgements This study was carried out in the Department of Physical Medicine and Rehabilitation, Institute of Clinical Medicine, and the Department of Public Health Science and General Practice, Institute of Health Sciences, University of Oulu, and Medical Research Center Oulu, Oulu University Hospital, during the years 2005–2015. I owe my deepest gratitude to Professor Jaro Karppinen, the main supervisor of the study, for his optimistic and persevering guidance through these years. His RYHUZKHOPLQJHQWKXVLDVPDQGFRPPLWPHQWWRVFLHQWL¿FZRUNDQGVXSHUYLVLRQRI VWXGLHVGHVHUYHVP\KXPEOHDQGKHDUWIHOWWKDQNV+HKDVKHOSIXOO\RIIHUHGPHWKH latest science news and encouraged me to have faith in my own abilities. I also want to express my gratitude to the second supervisor of the original publications, Docent Simo Taimela, who has been an essential help in designing and polishing RULJLQDOSXEOLFDWLRQVDQGDERYHDOOLQWKH¿HOGRIHSLGHPLRORJ\ ,DPYHU\JUDWHIXOWR(YHOLLQD+HLNNDIRUFROODERUDWLQJDQGZULWLQJWKHIRXUWK original publication together with me. I am also grateful to my other co-authors. -DDQD /DLWLQHQ 3K' 7XLMD 7DPPHOLQ 3K' .DLVX .DLNNRQHQ 06F DQG Professor Raija Korpelainen gave their expertise and helped me especially with the ¿UVWRULJLQDOSXEOLFDWLRQ'RFHQW3lLYL/HLQR$UMDVUHFHLYHVVSHFLDODWWHQWLRQDQG P\ZDUPHVWWKDQNVIRUKHUDFWLYHSDUWLFLSDWLRQDQGFRQVWUXFWLYHDQGHGXFDWLRQDO help in writing the second and third original publications. I am grateful for the help RI 3URIHVVRU (LUD 9LLNDUL-XQWXUD DQG 'RFHQW 7XRPR 3LHQLPlNL RQ ZRUNUHODWHG issues that were not so familiar to me before this study. They gave me solid support WR¿QLVKWKHVWXG\,DPWKDQNIXOWR3DDYR=LWWLQJ0'0DUNNX.RLUDQHQ-XKD $XYLQHQ3K'DQG0DUNXV3DDQDQHQ3K'IRUWKHLUNQRZOHGJHDQGORQJODVWLQJ KHOSZLWKWKHFRKRUWGDWD'RFHQW6YHWODQD6RORYLHYDLVDFNQRZOHGJHGZLWKUHVSHFW IRUDFFHSWLQJWKHFKDOOHQJLQJZRUNZLWKVWDWLVWLFDOGLI¿FXOWLHVZKHQ,KDGDOPRVW ORVWP\EHOLHILQVXFFHVV,WLVKDUGWR¿QGWKHULJKWZRUGVWRH[SUHVVP\JUDWLWXGHWR -RXNR5HPHV06FZKRKDVVSHQWKXJHQXPEHUVRIZRUNLQJKRXUVRQWKLVSLHFH RIZRUNDQGWLUHOHVVO\KHOSHGPHZLWKVWDWLVWLFV ,DPWKDQNIXOWR3URIHVVRU0DUMR5LLWWD-lUYHOLQZKRJDYHXVWKHRSSRUWXQLW\ WR XVH WKH FRKRUW GDWD , H[SUHVV P\ ZDUP WKDQNV WR 'RFHQW (HUR .\OO|QHQ DQG Professor Osmo Tervonen, who have followed and guided me during this process. 3URIHVVRU&KDUORWWH/HERHXI
GHDU JRGPRWKHU (OLQD 0lPPL IRU WKH UHYLVLRQ RI WKH )LQQLVK ODQJXDJH RI WKLV manuscript. I am grateful to my sister, friend and researcher Tuire, since her realistic and humorous words of consolation have always helped and encouraged me to go on ZLWKWKHZRUN,ZDQWWRWKDQNP\GHDUIULHQGVDQGFROOHDJXHV$QQD0DLMD.DWUL 0DUMD/LLVD .DM -DQL +DQQD$NL 0DXUL 0RQD 3lLYL$UL0DWWL 5LLWWD 6RLOH DQG.DWMDIRUVXSSRUWLQJPH\HDUE\\HDUZLWKWKLVSURMHFW,DOVRZDQWWRWKDQNDOO P\FRZRUNHUVLQ2XOX8QLYHUVLW\+RVSLWDOIRUWKHLUHQFRXUDJHPHQWDQGSDWLHQFH LQHYHU\GD\OLIHZLWKP\UHVHDUFKZRUN I wish to express my warmest gratitude to my family, close relatives and friends IRUWKHLUHQFRXUDJHPHQWDQGWROHUDQFH,ZDUPO\WKDQNP\GHDUVRQ-DDNNRIRUKLV help with computers, and my lovely daughters, Piia and Tiia, and their families for supporting me. My precious grandchildren have given me perspective and the EHVWUHZDUG±P\RZQSODFHLQWKHFKDLQRIJHQHUDWLRQVDVDJUDQGPRWKHU)LQDOO\ ,RZHP\ZDUPHVWWKDQNVWRP\GDUOLQJKXVEDQG3HNNDIRUKLVORYLQJVXSSRUWDQG unending care during these years together. 2XOX6HSWHPEHU

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Abbreviations $+$  $,&  $8&  %',  BIC BMI CDS &,   DD GHQ ,&' ICT ID /%3  /%7  /&$  /57  093$  N 1)%& 2%6  OR 3   3+$  PR 55   SD 6'4  SES 6366  66$%,& 86$  9$6  WC

$PHULFDQ+HDUW$VVRFLDWLRQ $NDLNH,QIRUPDWLRQ&ULWHULRQ $UHDXQGHUWKHFXUYH %HFN'HSUHVVLRQ,QYHQWRU\ Bayesian Information Criterion Body mass index Children’s Depression Scale &RQ¿GHQFHLQWHUYDO Disc degeneration General Health Questionnaire ,QWHUQDWLRQDO&ODVVL¿FDWLRQRI'LVHDVHVWK5HYLVLRQ Information and communication technology Identity /RZEDFNSDLQ /RZEDFNWURXEOH /DWHQWFODVVDQDO\VLV 9XRQJ/R0HQGHOO5XELQOLNHOLKRRGUDWLRWHVW 0RGHUDWHWRYLJRURXVOHLVXUHWLPHSK\VLFDODFWLYLW\ Number of participants 1RUWKHUQ)LQODQG%LUWK&RKRUW 2XOX%DFN6WXG\ Odds ratio 6WDWLVWLFDOVLJQL¿FDQFH 3K\VLFDODFWLYLW\ Prevalence ratio 5LVNUDWLR Standard deviation 6WUHQJWKDQG'LI¿FXOWLHV4XHVWLRQQDLUH Socioeconomic status 6WDWLVWLFDOSDFNDJHIRUWKHVRFLDOVFLHQFHV 6DPSOHVL]HDGMXVWHG%,& 8QLWHG6WDWHVRI$PHULFD 9LVXDO$QDORJXH6FDOH Waist circumference

11

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:RUOG+HDOWK2UJDQL]DWLRQ :RUOG0HGLFDO$VVRFLDWLRQ Youth Self-Report

List of original publications This thesis is based on four original publications*, which are referred to in the text by their Roman numerals. ,

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* Some unpublished data is also presented concerning the family’s socioeconomic status. ‚7KHVHDXWKRUVFRQWULEXWHGHTXDOO\WRWKLVZRUN

13

14

Contents Abstract Tiivistelmä Acknowledgements 9 Abbreviations 11 List of original publications 13 Contents 15 1 Introduction 17 2 Review of the literature 19 2.1 General overview .................................................................................... 19  2FFXUUHQFHRIORZEDFNSDLQLQDGROHVFHQFH.......................................... 19  3RWHQWLDOULVNIDFWRUVIRUORZEDFNSDLQLQDGROHVFHQFH.......................... 22 2.3.1 Genetic factors ............................................................................. 22 2.3.2. Overweight and obesity ............................................................... 23  6PRNLQJ ....................................................................................... 25  3K\VLFDODFWLYLW\DQGLQDFWLYLW\ ....................................................   :RUNORDG ...................................................................................... 29  3V\FKRVRFLDOIDFWRUV ..................................................................... 33  6OHHS ............................................................................................   3K\VLFDOIDFWRUV ............................................................................  2.3.9 Clustering of psychosocial and lifestyle factors .......................... 39  6XPPDU\RIWKHOLWHUDWXUHRQSRWHQWLDOULVNIDFWRUVIRUORZEDFNSDLQ ...  3 Purpose of the study 43 4 Material and methods 45  6WXG\GHVLJQDQGSRSXODWLRQ...................................................................   6WXG\HWKLFV.............................................................................................   5HSUHVHQWDWLYHQHVVRIWKHSRSXODWLRQ .....................................................   $VVHVVPHQWRIORZEDFNSDLQ..................................................................   ([SODQDWRU\YDULDEOHV .............................................................................   /LIHVW\OHIDFWRUV ...........................................................................   3K\VLFDOZRUNORDG ........................................................................ 51  3V\FKRVRFLDOIDFWRUV ..................................................................... 52  2WKHUPHDVXUHPHQWV..................................................................... 

15

 6WDWLVWLFDOPHWKRGV ..................................................................................   7KHDUHDXQGHUWKHFXUYH$8& PHWKRG .....................................   /DWHQW&ODVV$QDO\VHV/&$ ....................................................... 55  'HVFULSWLRQRIWKHLQGLYLGXDOVWXGLHV ...........................................  5 Results 59 5.1 Characteristics of the study population .................................................. 59  3UHYDOHQFHRIORZEDFNSDLQLQWKH2%6FRKRUW .....................................   $VVRFLDWLRQVEHWZHHQSRVVLEOHFRQIRXQGHUVDQGORZEDFNSDLQ ............   $VVRFLDWLRQVEHWZHHQSRVVLEOHULVNIDFWRUVDQGORZEDFNSDLQ ..............   :HLJKWUHODWHGIDFWRUVVWXG\, ....................................................   6PRNLQJVWXG\,, .......................................................................   3K\VLFDOZRUNORDGVWXG\,,, .......................................................   )DPLO\¶VVRFLRHFRQRPLFVWDWXVDQGORZEDFNSDLQ ......................   &RRFFXUUHQFHRISV\FKRVRFLDODQGOLIHVW\OHIDFWRUVVWXG\,9 ..  5.5 Summary of the main results of the thesis ..............................................  6 Discussion 97  0DLQ¿QGLQJV ..........................................................................................   0HWKRGRORJLFDOFRQVLGHUDWLRQV ...............................................................   &RPSDULVRQRISUHYLRXVVWXGLHV ........................................................... 102  2YHUZHLJKW ................................................................................. 102  6PRNLQJ .....................................................................................   3K\VLFDOZRUNORDG ......................................................................   6RFLRHFRQRPLFIDFWRUV ............................................................... 109  &OXVWHULQJRISV\FKRVRFLDODQGOLIHVW\OHIDFWRUV ........................ 110  6LJQL¿FDQFHRIWKHVWXG\....................................................................... 112 7 Conclusion 115 References 117 List of original publications 133

16

1

Introduction

7KHULVNIDFWRUVIRUORZEDFNSDLQ/%3 KDYHEHHQVWXGLHGH[WHQVLYHO\GXULQJWKH last decades, but still the understanding of the nature of LBP is limited (Koes & van 7XOGHUYDQ7XOGHU .RHV $VDFRPPRQFRQGLWLRQWKHSUHVHQFHRI /%3KDVDQLQÀXHQFHRQSXEOLFKHDOWK(YHQWKRXJK/%3LVQRWDGLVHDVHLWFDXVHV economical burden to the communities as well as suffering to the symptomatic SHUVRQV (KUOLFK  :+2 FDWHJRUL]HV KHDOWK GHWHUPLQDQWV LQWR SHUVRQDO DQG HQYLURQPHQWDO IDFWRUV DQG KDV UHSRUWHG D EDVLF FODVVL¿FDWLRQ RI IXQFWLRQLQJ DQG GLVDELOLW\IRU/%3&LH]Det al. 5LVNIDFWRUVRI/%3DUHFRPPRQO\FODVVL¿HG LQWRIDFWRUVWKDWDUHFRQQHFWHGWRJHQHWLFRUHQYLURQPHQWDOLQÀXHQFHV1RQJHQHWLF ULVNIDFWRUVRULQGLFDWRUVIRU/%3FDQDOVREHJURXSHGLQWRLQGLYLGXDOSV\FKRVRFLDO DQG SK\VLFDO OHLVXUH WLPH RU ZRUNUHODWHG  IDFWRUV $GDPV et al.  ±  $PRQJDGROHVFHQWVZRUNLQJKDVEHHQFODVVL¿HGDVDQLQGLYLGXDOOLIHVW\OHIDFWRU DV ZHOO $GDPV et al.   $OO WKHVH IDFWRUV FDQ LQWHUDFW LQWULFDWHO\ ZLWK HDFKRWKHU$GDPV et al. ,QGLYLGXDOIDFWRUVLQFOXGHJHQGHUDQGDJHDV well as lifestyle factors that are connected to health behaviour, such as physical DFWLYLW\ VPRNLQJ DQG RYHUZHLJKW RU REHVLW\ $GDPV et al.  ±  7KH ELRSV\FKRVRFLDO PRGHO RI EDFN SDLQ WDNHV LQWR FRQVLGHUDWLRQ SK\VLFDO ERG\  SV\FKRORJLFDOPLQG DQGVRFLDOHQYLURQPHQW DVSHFWVRISDLQ$GDPVet al. 7UXFKRQ  )LOOLRQ :DGGHOO   5LVN IDFWRUV PD\ DOVR EH FODVVL¿HG DV QRQPRGL¿DEOH IDFWRUV VXFK DV DJH DQG JHQGHU DQG SRWHQWLDOO\ PRGL¿DEOH factors, such as factors that are related to voluntary health behaviour and unhealthy HQYLURQPHQWDOVWUHVVRUVIRUH[DPSOHDWVFKRRORULQWKHZRUNSODFH$GDPVet al.   7KHUHVHDUFKSULRULWLHVFRQFHUQLQJWKHULVNIDFWRUVRI/%3KDYHPRVWO\EHHQ in adult populations (Balagué et al. 2012). Yet, the prevalence of LBP increases greatly during adolescence (Jeffries et al.  /HERHXI
RI PRGL¿DEOH ULVN IDFWRUV RI /%3 ZRXOG JLYH WKH RSSRUWXQLW\ WR GHVLJQ SURSHU preventive interventions. The present study used the multidimensional database IURP WKH DGROHVFHQW VXEFRKRUW RI WKH 1RUWKHUQ )LQODQG %LUWK &RKRUW  7KH main objective of this study was to increase the understanding of the potential PRGL¿DEOHIDFWRUVUHODWHGWR/%3LQDGROHVFHQFH The underlying hypothesis was that psychosocial and lifestyle factors, including ZRUNUHODWHGIDFWRUVDUHDVVRFLDWHGZLWK/%3LQDGROHVFHQFH$GGLWLRQDOO\ZHH[SHFWHG to see co-occurrence of psychosocial and lifestyle factors and the accumulation of unfavourable factors associated with LBP.

18

2

Review of the literature

2.1

General overview

Generally, LBP is considered as pain located in the area between the lower ribs and JOXWHDOIROGV1RQVSHFL¿F/%3LVGH¿QHGDVSDLQQRWDWWULEXWDEOHWRDUHFRJQLVDEOH VSHFL¿FSDWKRORJ\7KHWHUPORZEDFNWURXEOH/%7 LVDQXPEUHOODWHUPFRYHULQJ a wide spectrum of symptoms and pathology. Epidemiology is the study of the GLVWULEXWLRQDQGGHWHUPLQDQWVRIKHDOWKUHODWHGVWDWHVLQVSHFL¿HGSRSXODWLRQVDQG the application of this study to the prevention of health problems (Last 2001). In general, a cohort is just a group of people who share a common characteristic within DGH¿QHGSHULRG3URVSHFWLYHVLPSO\UHIHUVWRWKHIDFWWKDWWKHRXWFRPHLVPHDVXUHG at a later time point than the explanatory factor(s). $GROHVFHQFH LV GH¿QHG E\ WKH :RUOG +HDOWK 2UJDQL]DWLRQ :+2  DV WKH interval between 10 and 19 years of age. Early adolescence covers the years from WRDQGODWHDGROHVFHQFHWKH\HDUVIURPWR$GROHVFHQFHLVDSHULRGRIOLIH consisting of biological growth and maturation as well as educational, social and EHKDYLRXUDODVSHFWVDQGDOLIHFRXUVHIUDPHZRUNPXVWEHUHFRJQL]HGWRXQGHUVWDQG the whole spectrum of factors affecting adolescents’ health (Blum et al. 2012). The DJHRIWHQ\HDUVPDUNVWKHOLQHDIWHUZKLFKJURZWKSDWWHUQVGLYHUJHEHWZHHQJHQGHUV and individuals (Jeffries et al. 0RVWFRQYLQFLQJO\/%3LQDGROHVFHQFHKDV EHHQ OLQNHG WR SV\FKRVRFLDO ULVN IDFWRUV %DODJXp et al. 1995, Jones et al. 2003, Mustard et al.   DQG VPRNLQJ 6KLUL et al. 2010b). More controversially, it KDVDOVREHHQOLQNHGWRIHPDOHJHQGHU/HERHXI
Occurrence of low back pain in adolescence

Most people experience LBP at some point in life and LBP is a common condition already in childhood and adolescence (Jones & Macfarlane 2005). Theoretically, WKHUH DUH DFXWH VXEDFXWH FKURQLF ¿UVW RQVHW WUDQVLHQW DQG UHFXUUHQW ORZ EDFN 19

V\PSWRPV 3HULRGV RI SDLQ PD\ UHÀHFW ÀXFWXDWLQJ HSLVRGHV RI FKURQLF SDLQ RU HSLVRGHV RI DFXWH SDLQ LQWHUYDOV $GDPV et al.   ,Q SUHYLRXV VWXGLHV WKH GH¿QLWLRQRIµKHDOWK\¶DGROHVFHQWV¶V\PSWRPVKDVPRVWFRPPRQO\EHHQGHVFULEHG as general, chronic or recurrent, and severe or disabling LBP (Milanese & *ULPPHU6RPHUV   +RZHYHU WKH GLIIHUHQW FODVVL¿FDWLRQV RI VHOIUHSRUWHG LBP do not reveal the cause of pain. Observational studies of adolescent LBP KDYHPRVWFRPPRQO\XVHGTXHVWLRQQDLUHVWRFROOHFWWKHGDWDEXWDOVRLQWHUYLHZV H[DPLQDWLRQVDQGFRPELQDWLRQVRIWKHVHPHWKRGVKDYHEHHQXVHG&DOYR0XxR] et al.   )XUWKHUPRUH PRVW RI WKH VWXGLHV DUH VFKRROEDVHG DQG UHSUHVHQW (XURSHDQSRSXODWLRQV&DOYR0XxR]et al. 2013). In future, novel communication devices will possibly provide new opportunities towards diary-type data collection $[pQet al. 2012, Leboeuf-Yde et al. 2012). ,QFLGHQFHRIGLVHDVHLVGH¿QHGDVWKHUDWHRIRFFXUUHQFHRIQHZFDVHVDULVLQJLQ DJLYHQSHULRGLQDVSHFL¿HGSRSXODWLRQ%RQLWDet al. 3UHYDOHQFHLVGH¿QHG DVWKHIUHTXHQF\RIH[LVWLQJFDVHVLQDGH¿QHGSRSXODWLRQDWDJLYHQSRLQWRULQWHUYDO in time (Bonita et al. 7KHHSLVRGHVRIEDFNSDLQDUHRIWHQIRUJRWWHQ%XUWRQ et al. 7KHRSWLPDOSHULRGSUHYDOHQFHLQDGROHVFHQWVWXGLHVVHHPVWREHOHVV than 12 months because of memory decay (Milanese & Grimmer-Somers 2010). )XUWKHUPRUH WKH SUHYDOHQFH UDWHV DUH QRW FRPSDUDEOH ZKHQ GLIIHUHQW GH¿QLWLRQV of LBP have been used (Milanese & Grimmer-Somers 2010). Since 1991, the SUHYDOHQFH RI /%3 H[SHULHQFHG DW OHDVW ZHHNO\  KDV LQFUHDVHG DPRQJ )LQQLVK DGROHVFHQWV+DNDOD et al. $QLQFUHDVLQJWUHQGLVDOVRLQGLFDWHGLQWKHPRVW UHFHQWVWXGLHVLQWKHPHWDDQDO\VLV&DOYR0XxR]et al. 2013). In the following, a synopsis of the data on occurrence of LBP in adolescence is described. The prevalence of LBP increases greatly as early as between 12 and 20 years of age (Balagué et al.-HIIULHV et al./HERHXI
VWXGLHVZDVDQGWKHPHDQSHULRGSUHYDOHQFHRIPRQWKVIURPVWXGLHV ZDV7KHDGROHVFHQWVLQWKHVHVWXGLHVKDGWKHPHDQDJHRI\HDUVDQGWKH REWDLQHGOLIHWLPHSUHYDOHQFHRI/%3ZDVDERXW In a Canadian longitudinal school-based study among 502 adolescents around \HDUVRIDJHWKHPRQWKLQFLGHQFHRIWKH¿UVWLQWHUYDOZDVDQGWKDWRIWKH VHFRQGZKLOHWKH\HDUFXPXODWLYHLQFLGHQFHZDVZKHQ/%3ZDVGH¿QHG DV D SDLQ DW D IUHTXHQF\ RI DW OHDVW RQFH D ZHHN GXULQJ WKH SUHFHGLQJ VL[ PRQWKV )HOGPDQ et al.   ,Q D )LQQLVK VFKRROEDVHG SRSXODWLRQ RI  \HDUROG DGROHVFHQWV WKH \HDU SUHYDOHQFH RI LQWHUIHULQJ /%3 ZDV  6DOPLQHQ et al.  ,QD)LQQLVKQDWLRQZLGHSRSXODWLRQDPRQJVFKRROFKLOGUHQWKH\HDU SUHYDOHQFHRILQWHUIHULQJ/%3ZDVDPRQJDQG\HDUROGDGROHVFHQWVDQGQR gender differences were found (Taimela et al. $FFRUGLQJWRWKHQDWLRQDOFURVV VHFWLRQDOVWXGLHVLQ)LQODQGRI\HDUROGJLUOVDQGRIER\VUHSRUWHG/%3 RFFXUULQJDWOHDVWZHHNO\LQ7KHFRUUHVSRQGLQJSHUFHQWDJHVDW\HDUVZHUH RIJLUOVDQGRIER\V+DNDOD $VXPPDU\RIVWXGLHVRQRFFXUUHQFHRI /%3DPRQJDGROHVFHQWVZDVSXEOLVKHGLQWKHWKHVLVRI-XKD$XYLQHQ$XYLQHQ  (LJKW SHU FHQW RI )LQQLVK \HDUROG VFKRROFKLOGUHQ UHSRUWHG UHFXUUHQW RU FRQWLQXRXV /%3 DQG  RI WKHP H[SHULHQFHG DW OHDVW VRPH GLI¿FXOWLHV ZLWK daily activities (Salminen et al.   ,Q DQ (QJOLVK VWXG\ RI DERXW  HDUO\ DGROHVFHQWV  RI DGROHVFHQWV ZKR ZHUH UHSRUWLQJ /%3 H[SHULHQFHG DW OHDVW some interference with daily activities (Watson et al. $VWXG\FRQGXFWHGLQ WKH86$UHSRUWHGWKDWDERXWRQHWKLUGRIWKHDGROHVFHQWVUHSRUWLQJ/%3H[SHULHQFHG activity limitations (Olsen et al. 1992). Consultations for LBP in childhood are relatively uncommon (Burton et al.2OVHQ et al. 1992, Watson et al. 2002), EXW WKH SHUVLVWHQFH RI /%3 LV UHPDUNDEO\ FRPPRQ DV DERXW  RI DGROHVFHQWV UHSRUWLQJ/%3VWLOOUHSRUWHGV\PSWRPV\HDUVODWHU-RQHV 0DFIDUODQH  $PRQJ DGROHVFHQWV WKH LQWHQVLW\ RI SDLQ SUHGLFWHG SK\VLFLDQ FRQVXOWDWLRQV IRU FKURQLFSDLQDQGKLJKHUGLVDELOLW\ZDVDVVRFLDWHGZLWKDQLQFUHDVHGFDUHVHHNLQJ UDWH 3HUTXLQ et al. 2000, Vingilis et al.   ,Q WKH 2XOX %DFN 6WXG\ 2%6  SRSXODWLRQRIERWKJHQGHUVZKRZHUHUHSRUWLQJ/%3DW\HDUVKDGFRQVXOWHG a health care professional during the previous year because of their LBP (Tiira et al. 7KHFDUHVHHNLQJZDVVWURQJO\DVVRFLDWHGZLWKSDLQLQWHQVLW\DPRQJERWK genders and daily activity limitations among males. In summary, LBP is a common condition among adolescents and those with V\PSWRPVH[SHULHQFHTXLWHRIWHQVRPHGLI¿FXOWLHVZLWKGDLO\DFWLYLWLHVHYHQWKRXJK WKH\ GR QRW YHU\ RIWHQ VHHN PHGLFDO FDUH$V \HW WKHUH LV QR µJROG VWDQGDUG¶ WR measure LBP symptoms in epidemiological studies. 21

2.3

Potential risk factors for low back pain in adolescence

7KHWHUP³ULVNIDFWRU´ZDV¿UVWLQWURGXFHGLQWKH)UDPLQJKDP+HDUW6WXG\LQ 5LVNIDFWRU”refers to an aspect of personal habits or an environmental exposure that is associated with an increased probability of occurrence of a disease” (Bonita et al. $ULVNIDFWRUPD\H[SRVHWKHLQGLYLGXDOWRWKHFDXVDOFKDLQRUEHD SDUWRIWKHFDXVDOFKDLQ%HFN $FFRUGLQJWR+LOO¶VYLHZSRLQWV+LOO  however, there are some aspects that may help in determining if association is due to real causation. When another exposure exists in the population and is associated with the disease and the exposure being studied, it may constitute a confounding factor (Bonita et al. +HDOWKGHWHUPLQDQWLVGH¿QHGDVWKHVRFLDOHFRQRPLF cultural or environmental factor that is responsible for health and disease (Bonita et al. 3URWHFWLYHIDFWRUVHQKDQFHWKHOLNHOLKRRGRISRVLWLYHRXWFRPHDQGOHVVHQ WKHQHJDWLYHFRQVHTXHQFHVDPRQJWKRVHDWULVN.QRZOHGJHLVYHU\OLPLWHGRQWKH protective or preventive factors of LBP among children and adolescents (Cardon %DODJXp ,QWKHIROORZLQJVHFWLRQVWKHSRWHQWLDOULVNIDFWRUVRI/%3DUH UHYLHZHGDQGWKHHPSKDVLVLVSODFHGRQWKHSRWHQWLDOO\PRGL¿DEOHIDFWRUV 2.3.1 Genetic factors ,Q D 'DQLVK WZLQ VWXG\ WKH VKDUHG HQYLURQPHQW KDG DQ LPSRUWDQW LQÀXHQFH RQ lifetime prevalence of LBP until 15 years of age, after which the effect of the nonVKDUHG HQYLURQPHQW LQFUHDVHG DQG JHQHWLF IDFWRUV EHJDQ WR HPHUJH +HVWEDHN et al. $PRQJ\HDUROG)LQQLVKWZLQVWKHPDMRULW\RIWKHULVNRI/%3FRXOG be explained by environmental factors whereas genetic factors did not play an important role at this age (El-Metwally et al.  $FFRUGLQJWRWZLQVWXGLHVDPRQJDGXOWV/%3DQG''KDYHDJHQHWLFEDFNJURXQG .DOLFKPDQ  +XQWHU D .DOLFKPDQ  +XQWHU E  3URJUHVVLYH GLVF degeneration (DD) was the strongest predictor of severe LBP among female twins (MacGregor et al.   ,Q WKH )LQQLVK 6SLQH &RKRUW FRQVLVWLQJ RI PDOH WZLQV VWDWLVWLFDOO\VLJQL¿FDQWJHQHWLFFRUUHODWLRQVZHUHIRXQGIRUGLVFKHLJKWQDUURZLQJ DQGGXUDWLRQRIKRVSLWDOL]DWLRQIRUDQGGLVDELOLW\IURP/%3%DWWLH et al.  ,QDIHPDOHSRSXODWLRQFRQVLVWLQJRIWZLQVDQGVLQJOHWRQVJHQHWLFEDFNJURXQG was the major factor associated with LBP, but also advanced lumbar DD was D VLJQL¿FDQW ULVN IDFWRU 7KH FRQFOXVLRQ ZDV WKDW OXPEDU '' DQG /%3 VKDUH approximately 11–13% of the genetic effects (Livshits et al. 2011, MacGregor et al. $OVRJHQHWLFLQÀXHQFHPD\EHPHGLDWHGIRUH[DPSOHE\SV\FKRORJLFDO 22

determinants (Reichborn-Kjennerud et al. 2002), pain perception modulation )LOOLQJLPet al. VLJQDOOLQJSDWKZD\V'LDWFKHQNRet al. 2013) or immunityUHODWHGPHFKDQLVPV'RPLQLTXH]et al. 2013). In summary, non-genetic factors seem to be more essential for LBP in youth, ZKHUHDVJHQHWLFIDFWRUVPD\KDYHPRUHLQÀXHQFHZKHQLQGLYLGXDOVDUHROGHU 2.3.2 Overweight and obesity The prevalence of obesity among children and adolescents has increased during the last few decades (Kautiainen et al. 2002, Speiser et al. 2005). Nowadays, about WRRIVFKRRODJHGFKLOGUHQLQ)LQODQGDVZHOODVLQRWKHULQGXVWULDOL]HG counties are overweight (Kautiainen et al./REVWHLQ )UHOXW6SHLVHU et al. $QRYHUZHLJKWFKLOGLVOLNHO\WREHFRPHDQRYHUZHLJKWDGXOW(ULNVVRQ et al. 2003, Guo et al. 2002, Laitinen et al.  $ PRUH SDVVLYH OLIHVW\OH DQG overnutrition are the most important factors for obesity (Daniels et al. 2005, Haslam & James 2005). In epidemiological studies, body mass index (BMI) is the PRVWZLGHO\XVHGPHWKRGIRUWKHPHDVXUHPHQWRIRYHUZHLJKWDQGREHVLW\$VERG\ FRPSRVLWLRQFKDQJHVGXULQJJURZWKWKHGH¿QLWLRQVRIRYHUZHLJKWDQGREHVLW\DUH EDVHG RQ LQWHUQDWLRQDO FXWRII SRLQWV LQ HDFK DJH DQG JHQGHUVSHFL¿F SHUFHQWLOH of BMI (Cole et al. $FFRUGLQJWRWKH$PHULFDQ+HDUW$VVRFLDWLRQ$+$  FKLOGUHQDQGDGROHVFHQWVDUHRYHUZHLJKWZKHQWKHLU%0,LVEHWZHHQth and 95th percentile and obese when their BMI exceeds the 95th percentile (Daniels et al. 2005). It has been suggested that mechanical load, which increases by overweight, FRXOGKDVWHQWKHGHJHQHUDWLRQRIWKHVSLQH$GDPV 5RXJKOH\ RUWKDWWKH metabolic activity of adipose tissue of an obese person could increase pain (Rosen 6SLHJHOPDQ  $ SUHYLRXV UHYLHZ RQ WKH UHODWLRQ EHWZHHQ RYHUZHLJKW DQG /%3 UHSRUWHG LQFRQVLVWHQW ¿QGLQJV /HERHXI
LBP (Mustard et al. 2005). This Canadian study pooled both genders together. In a Danish twin population, being overweight at 12 to 22 years, was not associated ZLWK ODWHU DGXOW /%3 +HVWEDHN et al. D  7ZR )LQQLVK IROORZXS VWXGLHV among adolescents reported no association between base-line weight and later LBP (Nissinen et al.6DOPLQHQ et al. $SURVSHFWLYH(QJOLVKVFKRROEDVHG cohort study reported similar negative results between BMI or its change and LBP during the follow-up year (Jones et al. ,QDSURVSHFWLYH)LQQLVKELUWKFRKRUW VWXG\ RYHUZHLJKWREHVLW\ ZDV DVVRFLDWHG ZLWK DQ LQFUHDVHG ULVN RI VHFRQGWLPH KRVSLWDOL]DWLRQIRUVXUJLFDOWUHDWPHQWIRUVFLDWLFDDPRQJIHPDOHV5LYLQRMDet al. 2011). Cross-sectional studies among adolescents have reported mostly negative, but sometimes also positive associations between weight and LBP (Jones & Macfarlane 2005). $PRQJ )LQQLVK \RXQJ DGXOWV DJHG  WR  DEGRPLQDO REHVLW\ PHDVXUHG by waist circumference (WC)) was associated with LBP among females (Shiri et al. :DLVWWRKLSUDWLRDQGERG\IDWSHUFHQWDJHKDYHDOVREHHQXVHGLQWKH measurement of overweight and obesity in literature (Speiser et al. 2005). 3UHYLRXVO\''DW\HDUVKDVEHHQOLQNHGWRVHYHULW\RIORZEDFNV\PSWRPV LQWKHVDPH2%6FRKRUWSRSXODWLRQ7DNDWDOR et al. )XUWKHUPRUHKLJK%0, DW  \HDUV SUHGLFWHG '' LQ \RXQJ PDOHV LQ WKLV FRKRUW 7DNDWDOR et al. 2013). 2YHUZHLJKW DPRQJ \RXQJ PDOH DGXOWV KDV EHHQ VKRZQ WR LQFUHDVH WKH ULVN RI OXPEDU''ODWHULQPLGGOHDJH/LXNH et al. 2005). In a Chinese population-based VWXG\''ZDVDOVRDVVRFLDWHGZLWKRYHUZHLJKWDQGREHVLW\6DPDUW]LV et al. 2012). +RZHYHU DOVR RSSRVLWH ¿QGLQJV RQ WKLV LVVXH KDYH EHHQ SXEOLVKHG 9LGHPDQ et al. 2010). In a population-based study among female twins, heavier weight and BMI were associated with a higher grade of DD, which was associated with severe LBP (MacGregor et al. 7KXVLWLVXQFOHDUZKHWKHU''LVDPHGLDWLQJIDFWRU between obesity and LBP. ,Q FRQFOXVLRQ RYHUZHLJKWREHVLW\ VHHPV WR EH D SRVVLEOH ZHDN ULVN IDFWRU IRU/%3DPRQJDGXOWVHYHQWKRXJKWKHXQGHUO\LQJPHFKDQLVPLVVWLOOXQNQRZQ $PRQJ DGROHVFHQWV WKH HYLGHQFH KDV EHHQ PRVWO\ QHJDWLYH$ VXPPDU\ RI WKH above-mentioned longitudinal studies on BMI and LBP among adolescents is presented in Table 1.

24

Table 1. Summary of the longitudinal studies on body mass index (BMI) and LBP among adolescents and young adults. Study (country)

Population, methods

Main results

Jones et al. 2003 (England)

N = 1,046, 11–14 years, school-

BMI (or its change) was not

based, baseline, 12-month

associated with LBP in the

follow-up, weight and height

follow-up (data not shown)

measured /%3•GD\ GXULQJWKH preceding month Mustarad et al. 2005 (Canada)

N = 1,039, 4–16 years,

No association

population-based, weight and height measured at 8-year follow-up First episode of LBP during the preceding 12-months (“incident LBP”) Hestbaek et al. 2006a

N = 6,554, twins, 12–22 years at

No association between baseline

(Denmark)

baseline, 8-year follow-up, self-

overweight and LBP at follow-up

reported weight and height

No association in the twin control

LBP over 30 days during

analysis

the preceding 12-months (“persistent”)

2.3.3 Smoking 6PRNLQJLVDFRPPRQKDELWDPRQJDGROHVFHQWVHYHQWKRXJKLWKDVGHFOLQHGGXULQJ UHFHQWGHFDGHV5LPSHOl et al. 2003, Schepis & Rao 2005, Sourander et al. 2012). $OPRVWRQHWKLUGRIWKH)LQQLVKSRSXODWLRQDJHGWR\HDUVVPRNHGGDLO\LQ 5LPSHOl et al.  6PRNLQJFDXVHVYDVFXODUDQGUHVSLUDWRU\GLVHDVHVDQG cancer and shortens life expectancy by at least ten years (Jha et al. 2013, Smith et al.  ,WKDVDOVREHHQDVVRFLDWHGZLWKPXVFXORVNHOHWDOGLVRUGHUVDQGSDLQ-RKQ et al.3DOPHU et al. 2003). The previous two reviews on the association between VPRNLQJ DQG /%3 KDYH QRW IRXQG HQRXJK HYLGHQFH IRU FOHDU FRQFOXVLRQV 2QH UHYLHZUHSRUWHGLQFRQVLVWHQW¿QGLQJV/HERHXI
to be strongest for chronic or disabling LBP. The association between current VPRNLQJDQGWKHLQFLGHQFHRI/%3ZDVVWURQJHVWDPRQJDGROHVFHQWV,QD%ULWLVK ELUWKFRKRUWSHUVLVWHQWVPRNLQJGXULQJ\RXQJDGXOWKRRGZDVDVVRFLDWHGZLWK¿UVW ever LBP ten years later (Power et al. 2001). 3URVSHFWLYH VWXGLHV RQ VPRNLQJ DQG /%3 DPRQJ DGROHVFHQWV DUH IHZ ,Q D ORQJLWXGLQDO VWXG\ RI &DQDGLDQ DGROHVFHQWV DJHG DERXW  \HDUV ER\V DQG JLUOV FRPELQHG VPRNLQJLQFUHDVHGWKHULVNIRU/%37KHVWXG\VKRZHGDQH[SRVXUH UHVSRQVH UHODWLRQVKLS EHWZHHQ WKH DPRXQW VPRNHG DQG GHYHORSPHQW RI /%3 )HOGPDQ et al.   $FFRUGLQJ WR D ODUJHU FRKRUW VWXG\ RI &DQDGLDQ \RXQJ DGXOWVFXUUHQWKHDY\VPRNLQJLQFUHDVHGWKHULVNRI¿UVWHSLVRGHRI/%30XVWDUG et al. 2005). The adjusted odds ratios (OR) varied from 1.9 to 2.3 in these studies IRULQFLGHQW/%3,QD'DQLVKWZLQFRKRUWVPRNLQJZDVDVVRFLDWHGZLWKSHUVLVWHQW /%3DQGWKHUHVHHPHGWREHDGRVHUHVSRQVHUHODWLRQVKLSDWIROORZXS+HVWEDHNet al.D &URVVVHFWLRQDOVWXGLHVDPRQJDGROHVFHQWVKDYHUHSRUWHGLQFRQVLVWHQW ¿QGLQJV )LQGLQJV ZLWK SRVLWLYH *KDQGRXU et al.  +DUUHE\ et al. 1999, +HVWEDHNet al.D9LNDWet al. FRQÀLFWLQJ.ULVWMDQVGRWWLU 5KHH  and negative (Bejia et al. 2005, Kovacs et al. 2003) associations have been reported. ,Q D )LQQLVK FRKRUW RI DGROHVFHQWV GDLO\ VPRNLQJ ZDV DVVRFLDWHG ZLWK KRVSLWDOL]DWLRQV EHFDXVH RI /%3 GXULQJ WKH \HDU IROORZXS SHULRG 0DWWLOD et al. 6LPLODUO\VPRNLQJDW\HDUVRIDJHSUHGLFWHGKRVSLWDOL]DWLRQVUHODWHG to sciatica among males during adolescence and young adulthood (Rivinoja et al.   ,Q D ODUJH &DQDGLDQ SRSXODWLRQEDVHG FRKRUW VWXG\ \RXQJ GDLO\ VPRNHUV DJHGIURPWR\HDUVZHUHDWKLJKHUULVNRI/%3WKDQROGHUVXEMHFWV$ONKHUD\I et al. 2010). In the youngest age group, the prevalence of LBP was almost two WLPHVKLJKHUFRPSDUHGWRQRQVPRNHUV25± DIWHUDGMXVWPHQWIRU%0, education and activity. ,QFRQFOXVLRQVPRNLQJVHHPVWREHDVVRFLDWHGZLWK/%3EXWWKHUHDUHRQO\ IHZORQJLWXGLQDOVWXGLHVDPRQJDGROHVFHQWVRQWKLVWRSLF$VXPPDU\RIWKHFRKRUW VWXGLHV RQ VPRNLQJ DQG /%3 DPRQJ DGROHVFHQW DQG \RXQJ DGXOWV DV GHVFULEHG above is presented in Table 2.

26

Table 2. Summary of the cohort studies on smoking and LBP among adolescents and young adults. Study (country)

Population, methods

Main results, associations (95% CI)

Feldman et al. 1999, Feldman

N = 377 (no LBP at baseline),

27% smokers

et al. 2001 (Canada)

12–14 years, school-based,

Current smoker vs. non-smoker OR

6-months and 1-year follow-up

2.20 (1.38–3.50)

LBP at least once a week

Light to moderate smoker (1–25

during preceding 6-months

cig/week) vs. non-smoker OR 2.28 (1.15–4.51) Heavy (>25 cig/week) smoker vs. non-smoker OR 3.78 (0.82–17.51)

Mustard et al. 2005 (Canada)

N = 1,039 (4–16 years at

About 30% smokers

baseline), population-based,

Light smoker (1–9 cig/day) vs. non-

21–34 years at follow-up,

smoker OR 1.63 (0.92–2.91)

when smoking was assessed

+HDY\VPRNHU•FLJGD\ 25

retrospectively

1.85 (1.10–3.10)

First episode of LBP during the preceding 12-months (“incident LBP”) Hestbaek et al. 2006a

N = 6,554, twins, 12–22 years

21% had smoked (ever) at baseline

(Denmark)

at baseline, 20–30 years at

Smoking OR¹ 1.77 (1.44–2.17),

follow-up

according to smoked cig OR¹ 1.38

(baseline¹ and follow-up²; no

(1–10 cig/day), 2.00 (11–20 cig/

LBP at baseline)

day), 6.38 (>20 cig/day)

LBP over 30 days during

Smoking OR² 1.88 (1.32–2.69),

the preceding 12-months

according to smoked cig OR² 1.76,

(“persistent”)

2.12, -

N = 72,378, nationwide,

22% (female),25% (male) daily

population-based, 14–18 years

smoking

at baseline, about 11 years

Daily smoking OR 1.4 (1.1–1.7)

Mattila et al. 2008 (Finland)

follow-up LPB hospitalization

27

2.3.4 Physical activity and inactivity Studies focusing on the level of physical activity have investigated either physical activity or inactivity, or both together. In a Dutch cross-sectional population-based study, both very sedentary lifestyle and strenuous physical activities increased the ULVNRIFKURQLF/%3HVSHFLDOO\DPRQJIHPDOHV+HQHZHHU et al. 2009). The evidence IURPV\VWHPDWLFUHYLHZVFRQFHUQLQJSK\VLFDODFWLYLW\DQG/%3LVFRQÀLFWLQJEXW D ZHDN DVVRFLDWLRQ LV VXJJHVWHG +HQHZHHU et al.  6LWWKLSRUQYRUDNXO et al. 2011). The review on sedentary lifestyle and LBP found only limited evidence RQWKHLVVXHDQGFRQ¿UPHGWKDWLWLVQRWE\LWVHOIDVVRFLDWHGZLWK/%3&KHQ et al. 2009). The use of information and communication technology (ICT) has increased H[WUHPHO\DPRQJ)LQQLVKDGROHVFHQWVGXULQJWKHODVWWZRGHFDGHV+DNDOD  When the adolescent’s exposure time to computer use or playing digital games ZDVRYHUKGD\WKHULVNRIUHSRUWLQJ/%3ZDVVLJQL¿FDQWO\KLJKHUDFFRUGLQJWKH GDWDIURPWKH$GROHVFHQW+HDOWKDQG/LIHVW\OH6XUYH\+DNDOD et al.  The growing amount of inactivity due to ICT does not necessarily always reduce SK\VLFDO DFWLYLW\ 3DUWLFLSDWLRQ LQ IUHTXHQW PRGHUDWH WR YLJRURXV OHLVXUH WLPH SK\VLFDODFWLYLW\093$ KDVQRWGHFUHDVHGGXULQJWKHODVWGHFDGHVDPRQJ)LQQLVK adolescents (Nupponen et al. 2010). Hence, according to these observations, the same individuals might be both physically active and inactive, if these aspects are measured separately to form patterns of physical activity. This assumption is supported by the study that reported three distinct clusters of physical activity and VHGHQWDU\DFWLYLW\SDWWHUQVDPRQJ$PHULFDQDGROHVFHQWVZKHQGDWDZHUHJDWKHUHG from self-reports and accelerometer measurements from different physical activities DQGVHGHQWDU\EHKDYLRXUV+HLW]OHUet al. 2011). The relation between physical activity and LBP among adolescents seems WR EH 8VKDSHG -RQHV  0DFIDUODQH   &URVVVHFWLRQDO GDWDRQ WKH )LQQLVK population-based adolescent cohort supported the hypothesis of a U-shaped FRQQHFWLRQEHWZHHQSK\VLFDODFWLYLW\DQG/%3$XYLQHQ et al. 9HU\DFWLYH participation in physical activities was associated with reported LBP among both genders and high amount of sitting among girls. The reviews about adolescent surveys have reported that high levels of physical and sporting activity are related to LBP, but the evidence is mostly based on cross-sectional studies (Balagué et al.  &DUGRQ  %DODJXp  -RQHV  0DFIDUODQH   7KH SURVSHFWLYH VWXG\ RI (QJOLVK VFKRROFKLOGUHQ UHSRUWHG WKDW IUHTXHQW SDUWLFLSDWLRQ LQ VSRUWV LQFUHDVHGWKHULVNRI/%3DIWHURQH\HDUIROORZXS-RQHV et al. 2003). However, 28

VRPHSURVSHFWLYHVWXGLHVKDYHUHSRUWHGQRVXFKDVVRFLDWLRQV)HOGPDQ et al. 2001, 6DOPLQHQ $FFRUGLQJWRUHYLHZVWKHUROHRIVHGHQWDU\DFWLYLW\DQGSURORQJHG sitting for LBP among adolescents still remains controversial (Balagué et al. 1999, &DUGRQ  %DODJXp  -RQHV  0DFIDUODQH   0RVW RI WKH VXSSRUWLQJ evidence comes from cross-sectional studies; longitudinal studies do not support the connection (Jones et al. $FURVVVHFWLRQDOVXUYH\RI'DQLVKFKLOGUHQDQG adolescents reported no obvious association between objectively measured level RISK\VLFDODFWLYLW\DQG/%3:HGGHUNRSS et al. 2003). In addition to self-reports, they used accelerometers for a few days to evaluate the amount of physical activity. $FFRUGLQJWRWKHLUUHVXOWVWKHVHOIUHSRUWHGOHYHORISK\VLFDODFWLYLW\LVDQXQVXUH measure for research purposes. ,Q FRQFOXVLRQ WKH GH¿FLHQFLHV LQ WKH PHDVXUHPHQW RI SK\VLFDO DFWLYLW\ DQG LQDFWLYLW\LQHSLGHPLRORJLFDOVWXGLHVKDYHOLNHO\FDXVHGVRXUFHVRIHUURU&XUUHQWO\ WKHUHDUHPL[HGDQGLQVXI¿FLHQWGDWDRQWKHDVVRFLDWLRQEHWZHHQSK\VLFDODFWLYLW\ or inactivity and LBP among adolescents. However, it seems that moderate levels RISK\VLFDODFWLYLW\FRXOGEHUHFRPPHQGHGWRDGROHVFHQWVLQWHUPVRIEDFNLVVXHV 2.3.5 Workload :RUNLQJ LV TXLWH FRPPRQ DPRQJ )LQQLVK DGROHVFHQWV DQG SDUWWLPH ZRUN KDV EHFRPH HYHQ PRUH FRPPRQ LQ UHFHQW \HDUV $KR  6XODQGHU et al.   $OPRVWRQH¿IWKRIWKH)LQQLVKSRSXODWLRQ\RXQJHUWKDQ\HDUVRIDJHDUHWRVRPH H[WHQWHQJDJHGLQZRUNLQJEXWWZRRXWRIWKUHHRIWKHVHDUHVWXGHQWV$FFRUGLQJ WRD0LQQHVRWDKLJKVFKRROVXUYH\VL[W\SHUFHQWRIVWXGHQWVLQWKH86$KDGEHHQ ZRUNLQJUHJXODUO\VRPHWLPHVGXULQJWKHSUHYLRXV\HDU3DUNHU et al.  6SLQDOPHFKDQLFDOORDGKDVZLGHO\EHHQFRQVLGHUHGDVDULVNIDFWRUIRU/%3 DPRQJ DGXOWV $ UHFHQW V\VWHPDWLF UHYLHZ RI %DNNHU DQG FRZRUNHUV   LQFOXGHGSURVSHFWLYHFRKRUWVWXGLHVUHSRUWLQJLQFLGHQW/%36HYHQRIWKH VWXGLHVRQKHDY\SK\VLFDOZRUNDQG/%3UHSRUWHGQRVLJQL¿FDQWDVVRFLDWLRQDQG WKH\FRQFOXGHGWKDWWKHHYLGHQFHLVFRQÀLFWLQJ7KH\IRXQGVWURQJHYLGHQFHWKDW SURORQJHGVWDQGLQJRUZDONLQJDQGVLWWLQJDWZRUNDUHQRWDVVRFLDWHGZLWK/%3 7KHHYLGHQFHZDVFRQÀLFWLQJIRUWKHDVVRFLDWLRQEHWZHHQZRUNLQJZLWKEHQGLQJ RUWZLVWLQJSRVLWLRQVDQG/%37KHHYLGHQFHRIZKROHERG\YLEUDWLRQDVDULVN IDFWRUIRU/%3ZDVDOVRFRQÀLFWLQJ$SUHYLRXVV\VWHPDWLFUHYLHZDERXWSK\VLFDO ORDGIRU/%3RI+RRJHQGRRUQDQGFRZRUNHUV UHSRUWHGVWURQJHYLGHQFH for manual materials handling, bending and twisting, and whole-body vibration DV ULVN IDFWRUV7KH\ UHSRUWHG PRGHUDWH HYLGHQFH IRU KHDY\ SK\VLFDO ZRUN EXW 29

LQ WKH VHQVLWLYLW\ DQDO\VLV WKH ¿QGLQJV ZHUH LQFRQVLVWHQW DQG DVVRFLDWLRQ ZDV attenuated. There is also controversy regarding the connection with occupational OLIWLQJ RU DZNZDUG SRVWXUHV DQG /%3 5RIIH\ et al. 2010, Wai et al.  $ recent individual participant data meta-analysis found that posture and force were LQGHSHQGHQWO\ UHODWHG WR /%3 *ULI¿WK et al. 2012). In addition to the physical ZRUNORDGSV\FKRVRFLDOZRUNHQYLURQPHQWKDVEHHQVKRZQWREHDVVRFLDWHGZLWK LBP among adults (Hartvigsen et al./DQJ et al. 2012, Linton 2001, Sterud & Tynes 2013). $ %HOJLDQ FURVVVHFWLRQDO VWXG\ DPRQJ \RXQJ ZRUNHUV LQYHVWLJDWHG ZRUN UHODWHGULVNIDFWRUVIRU¿UVWHYHU/%3LQWKHLU¿UVWHPSOR\PHQW9DQ1LHXZHQKX\VH et al. ,QWKLVUHWURVSHFWLYHVWXG\WKHPHDQDJHRI\RXQJZRUNHUVZDV \HDUV)LUVWHYHUHSLVRGHVRI/%3ZHUHFRPPRQLQWKH¿UVW\HDURIHPSOR\PHQWDQG WKH\ZHUHDOVRDVVRFLDWHGZLWKVHDWHGZRUNÀH[LRQRUURWDWLRQPRYHPHQWVRIWKH WUXQNDQGDWOHDVW\HDUGXUDWLRQRIZRUNLQYROYLQJKHDY\OLIWLQJ $PRQJ DGROHVFHQWV WKHUH DUH IHZ VWXGLHV RQ WKH UHODWLRQVKLS RI SK\VLFDO ZRUNORDGZLWK/%3+DUUHE\DQGFRZRUNHUV ZHUHWKH¿UVWWRH[DPLQHWKH MREVLWXDWLRQDVDULVNIDFWRUIRU/%3DPRQJDGROHVFHQWV,QWKHLUFURVVVHFWLRQDO VXUYH\RIWR\HDUROG'DQLVKVFKRROFKLOGUHQKHDY\MREVLQOHLVXUH WLPHZHUHUHODWHGWRVHYHUH/%3+HDY\MREVZHUHGH¿QHGDVSHULRGLFRUFRQVWDQW KHDY\ORDGRQWKHEDFNIRUPRUHWKDQKRXUVSHUZHHN7KHFKLOGUHQUHSRUWHG WKDW WKH PRVW LPSRUWDQW VLWXDWLRQ SURYRNLQJ /%3 ZDV OLIWLQJ RU FDUU\LQJ KHDY\ REMHFWV7KHLU VWXG\ H[FOXGHG DGROHVFHQWV ZLWK PLQRU V\PSWRPV )XUWKHUPRUH part-time jobs were associated with LBP in an English cross-sectional study FRQVLVWLQJRIDERXWVFKRROFKLOGUHQDJHGWR\HDUV:DWVRQ et al. 2003). However, among those with part-time jobs, there was no association with reports RIOLIWLQJKHDY\REMHFWV7KH\LQFOXGHGHYHQVKRUWWHUPV\PSWRPV)XUWKHUPRUH the longitudinal analyses based on the same population concluded that children ZLWKDSDUWWLPHMREDWEDVHOLQHKDGLQFUHDVHGULVNRI/%3DWRQH\HDUIROORZXS (Jones et al. 2003). In a cross-sectional survey of low-income areas of Pelotas, %UD]LOPRQRWRQRXVZRUNDQGDZNZDUGSRVWXUHVZHUHDVVRFLDWHGZLWK/%3DPRQJ DGROHVFHQWV DJHG ± \HDUV ZKR ZHUH FXUUHQWO\ ZRUNLQJ Q    )DVVD et al.  $IWHU DGMXVWPHQW IRU FRQIRXQGLQJ IDFWRUV WKRVH LQ PDQXIDFWXULQJ UHSRUWHGPRUHEDFNSDLQWKDQFKLOGUHQQRWZRUNLQJZKLOHWKRVHZRUNLQJLQ GRPHVWLFVHUYLFHVKDGLQFUHDVHGULVNRIEDFNSDLQUHSRUWLQJ+RZHYHURQO\  DGROHVFHQWV ZHUH ZRUNHUV LQ PDQXIDFWXULQJ DQG UDQGRP HUURU LV SRVVLEOH These observations on child labour in a low-income population cannot be directly FRPSDUHGWRDGROHVFHQWZRUNLQDZHOIDUHVWDWH,QWKHORQJLWXGLQDOVWXG\RI 30

&DQDGLDQKLJKVFKRROVWXGHQWVDQDYHUDJHDJHRI\HDUV ZRUNLQJGXULQJWKH VFKRRO\HDUZDVDVVRFLDWHGZLWKGHYHORSPHQWRI/%3DQGPXVFXORVNHOHWDOSDLQ )HOGPDQ et al.  )HOGPDQ et al. 2002). During the 12-month follow-up, WKHGHYHORSPHQWRIPXVFXORVNHOHWDOV\PSWRPVZDVKLJKHVWLQZKLWHFROODUZRUN IROORZHG E\ EOXHFROODU ZRUN DQG ORZHVW LQ FKLOGFDUH ZRUN ,Q D 1RUZHJLDQ VWXG\ RI VFKRROFKLOGUHQ PDQXDO ZRUN DW EDVHOLQH ZDV DVVRFLDWHG ZLWK /%3 LQ WKH\HDUIROORZXS6MROLH +RZHYHUWKH\DSSDUHQWO\JDWKHUHGGDWDIURP VFKRRODQGKRPHEDVHGZRUN These few studies among adolescents reported different prevalences and types RIZRUNLQJDQGXVHGGLIIHUHQWGH¿QLWLRQVIRU/%31RQHWKHOHVVWKH\VXJJHVWWKDW ZRUNLQJLVDVVRFLDWHGZLWK/%3DPRQJDGROHVFHQWV7KHDGMXVWHGRGGVUDWLRV25  shown varied from 1.3 to 1.95. It should be noted that these studies considered GLIIHUHQWFRQIRXQGLQJIDFWRUVDQGQRQHRIWKHPHYDOXDWHGVRFLRHFRQRPLFVWDWXV$ VXPPDU\RIWKHVWXGLHVSUHVHQWHGDERYHWKDWLQYROYHZRUNLQJDQGDGROHVFHQW/%3 is presented in Table 3.

31

Table 3. Summary of the studies that involve working and adolescent LBP. Study (country)

Population, methods

Main results

Harreby et al. 1999 (Denmark)

N = 1,389, 13–16 years,

67% working, 22% heavy work

school-based, cross-sectional

Heavy work and severe LBP +

questionnaire

(OR 1.95)

5HFXUUHQW•/%3DWWDFNVSHU

Situations that were mostly

month) or continuous moderate

reported to provoke LBP:

to severe LBP

- Lifting/carrying heavy objects

Comments: did not consider

- Forward bending

psychosocial factors

- Sitting >1/2 hours

Feldman et al. 2001, 2002

N = 502, about 14 years, school-

63% working

(Canada)

based, baseline (N = 377 no

Working during school year and

LBP) + 6-month + 12-month

LBP + (OR 1.33)

questionnaire

White-collar work and LPB +

LBP at least once a week during

(OR 4.85)

preceding 6-months (2001),

Blue-collar work or child care

musculoskeletal pain (2002)

work and LBP – 12-month: work and LBP –

Watson et al. 2003 (England)

N = 1,446, 11–14 years,

25% working

school-based, cross-sectional

Part time job and LBP +

questionnaire

(multivariate model OR 1.4)

/%3•GD\ GXULQJWKH

Lifting heavy items and LBP –

preceding month Comments: did not consider smoking Jones et al. 2003 (England)

N = 1,046, 11–14 years, school-

?% working (not reported)

based questionnaire, baseline

Part-time job and LBP + (RR

(no LBP) + 12 month follow-up

1.5)

(N = 933)

Job type, the weekly working

/%3•GD\ GXULQJWKH

time, and lifting heavy items and

preceding month

LBP –

Comments: adjustment for age and gender Fassa et al. 2005 (Brazil)

32

N = 3,269, 10–17 years,

14% currently working

population-based, interview,

Monotonous work (prevalence

cross-sectional

ratio PR = 1.34), awkward

LBP during the preceding year

posture (PR = 1.31), and

Comments: did not consider

QRLVH35  VLJQL¿FDQWO\

psychosocial factors or BMI

associated with LBP

2.3.6 Psychosocial factors :+2KDVGH¿QHGSV\FKRVRFLDOIDFWRUDVDQ\IDFWRUGHWHUPLQLQJWKHZD\DSHUVRQ is able to “deal effectively with the demands and challenges of everyday life […], to maintain a state of mental well-being and to demonstrate this in adaptive and positive behaviour while interacting …” :+2 'LVWUHVVKDVEHHQGH¿QHG LQ YDULRXV GLFWLRQDULHV DV D QHJDWLYH VWUHVV UHVSRQVH ZLWK LQVXI¿FLHQW DGDSWDWLRQ causing extreme feelings of anxiety, sorrow or pain. However, in a medical context the term depression refers to a mental state dominated by a lowering of mood and loss of interest and enjoyment, often accompanied by various symptoms, and EHKDYLRXUDO DQG WKRXJKW FKDQJHV ,&'  )XUWKHUPRUH GHSUHVVLRQ DQG DQ[LHW\ often occur together (ICD10). The term anxiety is used for feelings of tension, worried thoughts and accompanying physical reactions (ICD10). Psychological and behavioural problems among children and adolescents have also been divided LQWRLQWHUQDOL]LQJDQGH[WHUQDOL]LQJSUHVHQWDWLRQV$FKHQEDFK 5HVFRUOD  $FFRUGLQJ WR WKLV GLYLVLRQ LQWHUQDOL]LQJ LQGLYLGXDOV IRFXV WKHLU EHKDYLRXUV inward and are more prone to have symptoms such as depression, worry or fear. ([WHUQDOL]LQJLQGLYLGXDOVDUHPRUHIRFXVHGWRZDUGRWKHUVDQGWKHLUV\PSWRPVPD\ LQFOXGH FRQGXFW GLVRUGHUV UXOHEUHDNLQJ DQG DJJUHVVLYH EHKDYLRXUV 7KH WHUP ³\HOORZÀDJV´KDVEHHQXVHGWRGHVFULEHSV\FKRVRFLDOSURJQRVWLFIDFWRUVIRUSRRU outcome or recovery (Nicholas et al. 2011). It has newly been recommended that instead of studying which psychosocial factors have an impact, researchers should concentrate on which of them are the most central ones (Nicholas et al. 2011). The relationships between contributory factors may be bidirectional and there may also be interdependence between them (Ramond et al.  $GGLWLRQDOO\ HQYLURQPHQWDOVWUHVVRUVDQGWLPLQJPD\LQÀXHQFHWKHUHVSRQVHVRIWKHLQGLYLGXDOV (Ramond et al. 2011). The studies presented in the current literature review have used various methods for psychological assessment, and therefore they provide heterogeneous LQIRUPDWLRQ7KHUHYLHZRISURVSHFWLYHVWXGLHVRQSV\FKRVRFLDOULVNIDFWRUVDPRQJ DGXOWVFRQFOXGHGWKDWWKHUHLVDFOHDUOLQNEHWZHHQSV\FKRVRFLDOYDULDEOHVDQG/%3 (onset of pain, acute, subacute, and chronic pain) (Linton 2000). Methodological TXDOLW\ RI WKH VWXGLHV YDULHG FRQVLGHUDEO\ HYHQWXDOO\  VWXGLHV IXO¿OOHG WKH VHOHFWLRQ FULWHULD 3V\FKRVRFLDO YDULDEOHV ZHUH SDUWLFXODUO\ OLQNHG WR WUDQVLWLRQ to chronic problems. Passive coping, pain cognitions and fear-avoidance beliefs ZHUH UHODWHG WR SDLQ DQG GLVDELOLW\ DPRQJVW FRJQLWLYH IDFWRUV$OVR GHSUHVVLRQ DQ[LHW\ GLVWUHVV DQG HPRWLRQV ZHUH UHODWHG WR SDLQ DQG GLVDELOLW\ $QRWKHU 33

UHFHQW UHYLHZ DPRQJ DGXOWV VWXGLHG SV\FKRVRFLDO ULVN IDFWRUV DQG FKURQLF /%3 in primary care (Ramond et al. 7KH¿QDOGDWDFRYHUHGGLIIHUHQWFRKRUWV and concluded that depression, psychological distress, passive coping strategies and fear-avoidance beliefs were independently associated with transition to FKURQLFSDLQLQVRPHVWXGLHV7KHPRVWUHFHQWUHYLHZVWXGLHGSV\FKRVRFLDOZRUN stressors captured from longitudinal studies (Lang et al.   )LIW\ VWXGLHV IXO¿OOHGWKHVHOHFWLRQFULWHULD+LJKO\PRQRWRQRXVZRUNZDVWKHPRVWVLJQL¿FDQW SV\FKRVRFLDOULVNIDFWRUIRU/%3DVWKHSRROHG25ZDV&,± $OVR high job insecurity, low social or supervisor support, high job strain, high job demands, and low job control were associated with LBP. However, a previous review with different inclusion criteria found moderate evidence against an DVVRFLDWLRQ EHWZHHQ VRFLDO VXSSRUW DW ZRUN DQG /%3 +DUWYLJVHQ et al.   $ SURVSHFWLYH SRSXODWLRQEDVHG (QJOLVK VWXG\ DPRQJ DGXOWV FRQFOXGHG WKDW V\PSWRPVRISV\FKRORJLFDOGLVWUHVVSUHGLFWHGLQFLGHQW/%3VRWKDWRIQHZ episodes of LBP during one year were attributable to more serious psychological distress (Croft et al. 1995). The study used the General Health Questionnaire *+4  WR PHDVXUH SV\FKRORJLFDO GLVWUHVV$FFRUGLQJ WR WKH  %ULWLVK ELUWK FRKRUWVWXG\SV\FKRORJLFDOGLVWUHVVDW\HDUVRIDJHPRUHWKDQGRXEOHGWKHULVN of one-year incident LBP at 33 years of age (Power et al. 2001). They evaluated psychological distress via the Malaise Inventory-based scores. $UHFHQWUHYLHZRQULVNIDFWRUVRIFKLOGUHQDQGDGROHVFHQWVFRQFOXGHGWKDW WKHUH LV JRRG HYLGHQFH WKDW WKH FKLOGUHQ ZLWK /%3 DUH PRUH OLNHO\ WR UHSRUW negative psychosocial experiences and some evidence that psychosocial factors PD\SUHGLFWIXWXUH/%3-RQHV 0DFIDUODQH $6ZHGLVKIROORZXSVWXG\ among preadolescents and adolescents also reported associations with several psychosocial parameters (concerning e.g. conduct problems, emotions and stress) DQGIUHTXHQWV\PSWRPVRI/%3%UDWWEHUJ $Q(QJOLVKVWXG\DPRQJHDUO\ adolescents reported that psychological factors and other somatic pain symptoms predicted incident LBP during the one-year follow-up (Jones et al. 2003). They HYDOXDWHG SV\FKRVRFLDO IDFWRUV E\ WKH 6WUHQJWK DQG 'LI¿FXOWLHV 4XHVWLRQQDLUH (SDQ). Especially, belonging to the high tertile of conduct problems was DVVRFLDWHG ZLWK IXWXUH /%3 $ %HOJLDQ IROORZXS VWXG\ RI SUHDGROHVFHQW VFKRROFKLOGUHQ IRXQG QR VSHFL¿F SV\FKRVRFLDO ULVN IDFWRUV IRU LQFLGHQW /%3 6]SDOVNL et al. 2002). In a Canadian study among young adults, psychological GLVWUHVVLQDGXOWKRRGDQGHPRWLRQDORUEHKDYLRXUDOGLVRUGHUVDTXHVWLRQQDLUHIRU parents and children evaluating hyperactivity, conduct disorders, and emotional GLVRUGHUV  LQ FKLOGKRRG ZHUH DVVRFLDWHG ZLWK ¿UVW HSLVRGH RI /%3 0XVWDUG et 34

al. ,QD)LQQLVKIROORZXSVWXG\RISUHDGROHVFHQFHWRHDUO\DGROHVFHQFH PXVFXORVNHOHWDOSDLQUHFXUUHQFHZDVDVVRFLDWHGZLWKGHSUHVVLYHIHHOLQJVDPRQJ girls (El-Metwally et al.  The evidence from cross-sectional studies is mostly in line with longitudinal data, but the psychosocial parameters vary as well. Some examples of the studies DUH SUHVHQWHG LQ WKH IROORZLQJ ,Q D SRSXODWLRQEDVHG )LQQLVK FURVVVHFWLRQDO VWXG\RIWR\HDUROGVFKRROFKLOGUHQRIJLUOVDQGRIER\VUHSRUWHG PRGHUDWH WR VHYHUH GHSUHVVLRQ +lUPl et al.  $PRQJ WKHVH DERXW  adolescents, recurrent pain symptoms were associated with depression, which ZDV HYDOXDWHG YLD D LWHP YHUVLRQ RI WKH %HFN 'HSUHVVLRQ ,QYHQWRU\ %',  'HSUHVVLRQ ZDV VLJQL¿FDQWO\ DVVRFLDWHG ZLWK UHFXUUHQW /%3 DPRQJ JLUOV 25  DQGER\V25 ZLWKDGMXVWPHQWIRUDJHDQGDQ[LHW\+lUPlet al. 2002). $QRWKHU )LQQLVK VXUYH\ RI DERXW  DGROHVFHQWV UHSRUWHG WKDW /%3 ZDV associated with psychosomatic symptoms, the connection being stronger when WKHQXPEHURISV\FKRVRPDWLFV\PSWRPVLQFUHDVHG9LNDW et al. $Q(QJOLVK VWXG\RIDERXWHDUO\DGROHVFHQWVUHSRUWHGVWURQJDVVRFLDWLRQVZLWKHPRWLRQDO problems, conduct problems, other pains, and daytime tiredness and LBP (Watson et al.  7KH\ XVHG 6'4 WR PHDVXUH SV\FKRVRFLDO IDFWRUV$ VWXG\ RI DERXW 20-year-old college students in the United States reported that feeling very sad, exhausted, and overwhelmed associated with the prevalence of LBP in univariate analyses (Kennedy et al. $VWXG\RIWR\HDUROGDGROHVFHQWVLQ 6ZLW]HUODQGUHSRUWHGDOVRWKDWSV\FKRORJLFDOIDFWRUVZHUHDVVRFLDWHGZLWK/%3DQG VHHNLQJ FDUH IRU /%3 %DODJXp et al. 1995). They used the shortened Children’s 'HSUHVVLRQ6FDOH&'6 IRUSV\FKRORJLFDOSDUDPHWHUV$6ZLVVVWXG\RIDERXW children at the end of primary school considered teacher reports of school-type UHFRPPHQGDWLRQVDQGSXSLOV¶PDWKVJUDGHVDVREMHFWLYHSV\FKRVRFLDOULVNIDFWRUV in addition to self-reported psychosocial strain evaluated via SDQ (Erne & Elfering 2011). Both self-reported psychosocial strain and objective stress were associated with LBP in their study. LBP in adolescence has been reported to associate with co-occurring pain V\PSWRPVHVSHFLDOO\DPRQJJLUOV$XYLQHQ et al. 2009, Pellise et al.9LNDW et al. 2000). Subjective disabilities increase with the number of pain locations (Hoftun et al. 2011). Depression, somatic complains and pain symptoms may share common mechanisms (Greenspan et al.  Social and economic shortcomings are related to poor health among adolescents 3RZHU EXWWKHHYLGHQFHRQ/%3LVFRQÀLFWLQJ$'DQLVKWZLQVWXG\DPRQJ adolescents reported no association with socioeconomic parameters and LBP, but a 35

JRRGVRFLDOEDFNJURXQGSURWHFWHGDJDLQVWFKURQLFV\PSWRPV+HVWEDHN et al.  $QRWKHU'DQLVKVWXG\UHSRUWHGWKDWWKHUHLVDPRGHVWQHJDWLYHDVVRFLDWLRQEHWZHHQ parental education and LBP in preadolescents but not in adolescents (Leboeuf-Yde et al. )DWKHU¶VRFFXSDWLRQDOFODVVDQGOHYHORIHGXFDWLRQZHUHQRWDVVRFLDWHG ZLWK/%3DPRQJDGROHVFHQWVLQD)LQQLVKVWXG\EXWWKRVHZKRGLGQRWOLYHZLWK SDUHQWVKDGDKLJKHUULVNRI/%39LNDW et al. $1RUZHJLDQVWXG\UHSRUWHG also negative associations (Sjolie 2002). To pull together this information, psychosocial factors seem to be associated with LBP among adolescents. Unfortunately, there is no clear consensus of the best ZD\ WR PHDVXUH SV\FKRVRFLDO DVSHFWV DQG WKH UHVXOWV DUH GLI¿FXOW WR FRPSDUH$ summary of the above-mentioned longitudinal studies on psychosocial factors and DGROHVFHQW/%3LVSUHVHQWHGLQ7DEOH

36

Table 4. Summary of the longitudinal studies that involve psychosocial factors and LBP among adolescents. Study (country)

Population, methods

Main results, associations (95% CI)

Brattberg 1994 (Sweden)

N = 1,245, school-based

Fear of schoolmates, loneliness,

survey, 10–15 years at 2-year

GLI¿FXOWLHVWRPDNHIULHQGVIHHOLQJV

follow-up (N = 471)

of being an outsider, regularly

Recurrent, disabling LBP during

being bullied, passive reaction to

the preceding 6-months

bullying, nervousness, alexithymia,

Did not consider any

DQGGLI¿FXOWLHVLQDGXOWFRQGXFWV

confounding factors

were associated

N = 392, school-based survey,

No LBP was associated with

9–11 years at baseline, 2-year

general happiness adj. OR 1.26

follow-up

(1.09–1.45)

Szpalski et al. 2002 (Belgium)

No LBP (ever/recent) vs. LBP at baseline and follow-up Adjustment for other factors in the multivariate model Jones et al. 2003 (England)

N = 1,046, 11–14 years, school-

³7RWDOGLI¿FXOWLHV´VFRUH55

based questionnaire, baseline

(1.1–2.3)

(no LBP) + 12 month follow-up

Conduct problems (e.g. , anger,

(N = 933)

disobedience, violence) RR 2.5

/%3•GD\ GXULQJWKH

(1.7–3.7)

preceding month

1RVLJQL¿FDQWDVVRFLDWLRQV

Adjustment for age and gender

hyperactivity, emotional symptoms, peer problems

Mustard et al. 2005 (Canada)

N = 1,039, 4–16 years at

Emotional and behavioural

baseline, population-based,

disorders in childhood OR 1.87

21–34 years at follow-up

(1.02–3.42)

First episode of LBP during the

Prevalent psychological stress OR

preceding 12-months (“incident

1.86 (low) and OR 1.85 (moderate

LBP”)

to high) (1.14–3.03 and 1.07–3.02)

Adjustment for age, gender, childhood conditions, childhood health status, early adult health, behaviour, socioeconomic status, and work environment

37

2.3.7 Sleep ,Q )LQODQG ± RI DGROHVFHQWV UHSRUW VOHHS GLVWXUEDQFHV 7+/   6OHHS SDWWHUQVFKDQJHGXULQJDGROHVFHQFH&DUVNDGRQ0LOOPDQ+DJHQDXHU et al.   7KH FLUFDGLDQ UHJXODWLRQ XQGHUJRHV FKDQJHV ZKLFK PDNH LW HDV\ for adolescents to delay their bedtime (Hagenauer et al. $OVRVFUHHQWLPH VRFLDOQHWZRUNLQJDQGRWKHUW\SHVRISV\FKRVRFLDOSUHVVXUHLQWKHHYHQLQJGHOD\ WKHLU VOHHS &DUVNDGRQ   2Q WKH RWKHU KDQG WKH HDUO\ VWDUW RI VFKRRO GRHV QRW FKDQJH DW WKDW WLPH &DUVNDGRQ   ,W KDV EHHQ VWDWHG WKDW VOHHS QHHG GRHV QRW GHFOLQH GXULQJ DGROHVFHQFH &DUVNDGRQ   KRZHYHU WKHUH LV QR strong consensus regarding the recommended duration of sleep for adolescents )HLQEHUJ  0DWULFFLDQL et al. 2013). Sleep deprivation among adolescents KDVEHFRPHFRPPRQ&DUVNDGRQ0DWULFFLDQLet al. ,QVXI¿FLHQWVOHHS has been associated with many negative health effects, such as daytime sleepiness 0LNNHOVVRQet al.:DWVRQet al. 2003), mood disturbances (Millman 2005, Roberts et al.   EHKDYLRXU SUREOHPV 0LOOPDQ  5REHUWV et al.   overweight (Patel 2009), and immune system changes (Grandner et al. 2013). In a ORQJLWXGLQDOVWXG\DPRQJDGROHVFHQWVFKURQLFLQVRPQLDLQFUHDVHGVXEVHTXHQWULVN for interpersonal, psychological, and somatic health problems (Roberts et al.  ,QDQRWKHUORQJLWXGLQDOVWXG\LQVXI¿FLHQWTXDQWLW\RUTXDOLW\RIVOHHSDQGWLUHGQHVV ZHUH DVVRFLDWHG ZLWK /%3 DW WKH \HDU IROORZXS DPRQJ JLUOV $XYLQHQ et al.  'D\WLPHWLUHGQHVVKDVEHHQDVVRFLDWHGZLWK/%3DPRQJWR\HDUROG VFKRROFKLOGUHQDQGDOVRZLWKPXVFXORVNHOHWDOSDLQVDPRQJFKLOGUHQ0LNNHOVVRQ et al.  :DWVRQ et al.   6OHHS GLVWXUEDQFHV SUHGLFWHG KRVSLWDOL]DWLRQV FDXVHGE\EDFNGLVRUGHUVDPRQJDGXOWVLQDORQJIROORZXSVWXG\.DLOD.DQJDV et al. &RQWUROOHGVOHHSGHSULYDWLRQFDXVHGDOWHUDWLRQLQSDLQSHUFHSWLRQDQG HOHYDWHG9$6UDWLQJVDPRQJ\RXQJPDOHV$]HYHGR et al. 2011). Hence, sleep has become an interesting new area of pain research and there is some indication that it could also be related to LBP. 2.3.8 Physical factors The studies on individual physical characteristics and LBP have resulted in LQFRQVLVWHQW¿QGLQJV%DODJXpet al. 1999, Jones & Macfarlane 2005). There is no FOHDUDVVRFLDWLRQZLWKWUXQNPXVFOHVWUHQJWKDQG/%3DPRQJDGROHVFHQWV%DODJXp et al. 1999, Paalanne et al.   RU DGXOWV +DPEHUJYDQ 5HHQHQ et al.   7KH UHYLHZ IRXQG QR UHODWLRQVKLS EHWZHHQ WUXQN PXVFOH HQGXUDQFH DQG WKH ULVN 38

of LBP (Hamberg-van Reenen et al.   +RZHYHU LQ D ODUJH FURVVVHFWLRQDO VWXG\DPRQJDGROHVFHQWVORZLVRPHWULFPXVFOHHQGXUDQFHLQWKHEDFNH[WHQVRUV ZDVDVVRFLDWHGZLWK/%3EXWWKHUHZHUHQRDVVRFLDWLRQVEHWZHHQDHURELF¿WQHVV IXQFWLRQDO VWUHQJWK ÀH[LELOLW\ RU SK\VLFDO DFWLYLW\ DQG /%3 %R$QGHUVHQ et al.  /%3LQDGROHVFHQFHKDVDOVREHHQOLQNHGWRUDSLGJURZWKVSXUW3RXVVD et al. $QRWKHU)LQQLVKVWXG\IRXQGQRDVVRFLDWLRQEHWZHHQJURZWKRIKHLJKW DQG /%3 LQVWHDG DQ DVVRFLDWLRQ EHWZHHQ WUXQN DV\PPHWU\ DQG IXWXUH /%3 ZDV discovered (Nissinen et al.  7KH VWXGLHV RQ PHFKDQLFDO ORDG ZKLFK LV QRW UHODWHG WR ZRUN KDYH PRVWO\ evaluated if carrying heavy schoolbags could be injurious (Jones & Macfarlane   ,W VHHPV WKDW \RXQJ SXSLOV EHDU KHDYLHU ORDGV UHODWHG WR WKHLU RZQ VL]H (Limon et al. EXWWKHUHLVQRFOHDUHYLGHQFHIRULWVKDUPIXOQHVVDPRQJ\RXQJ or older pupils (Jones & Macfarlane 2005). 2.3.9 Clustering of psychosocial and lifestyle factors 7KH SUHYLRXV UHYLHZV RQ WKH ULVN IDFWRUV RI DGROHVFHQWV /%3 KDYH FKDUDFWHUL]HG the multidimensional nature of LBP consisting of unhealthy behaviours and psychosocial symptoms (Balagué et al.  &DUGRQ  %DODJXp  -RQHV & Macfarlane 2005). However, most of the surveys conducted have examined GHWULPHQWDO IDFWRUV DV VHSDUDWH SUHGLFWRUV 'DWD IURP WKH &DUGLRYDVFXODU 5LVN LQ
39

2.4

Summary of the literature on potential risk factors for low back pain

0RGL¿DEOH IDFWRUV SOD\ D UHOHYDQW UROH LQ /%3 DPRQJ DGROHVFHQWV )LJ    ,W seems that high physical activity and excessive inactivity are related to LBP, at OHDVWWRVRPHH[WHQW$GROHVFHQWVDOVRUHSRUWOHVVSDLQV\PSWRPVLIWKH\VOHHSZHOO 7KHUHLVVRPHHYLGHQFHDPRQJDGXOWVWKDWREHVLW\PD\EHDULVNIDFWRUIRUFKURQLF LBP. Even though obesity is a growing health problem, the existing limited followup data among children and adolescents being exposed does not convincingly VXSSRUWWKHUROHRIREHVLW\DVDULVNIDFWRURI/%3LQDGROHVFHQFH6RPHVWXGLHV LQGLFDWHWKDWVPRNLQJLQDGROHVFHQFHPD\SUHGLFW/%3DOUHDG\LQWKHVKRUWWHUPEXW WKHORQJWHUPHIIHFWVRIDGROHVFHQWV¶VPRNLQJDUHQRWNQRZQ:RUNLQJGXULQJWKH school year seems to be associated with reporting of LBP in adolescence. Studies RQVSHFL¿FSK\VLFDOZRUNORDGIDFWRUVIRU/%3DPRQJDGROHVFHQWVLQZHOIDUHVWDWHV are missing. Psychosocial factors are related especially to chronic LBP among adults and they seem to be related to LBP among adolescents, too. Psychosocial DQGOLIHVW\OHIDFWRUVWHQGWRRFFXUWRJHWKHU7KHLQÀXHQFHRIDFFXPXODWLRQRIWKHVH IDFWRUVRQRFFXUUHQFHRI/%3LQDGROHVFHQFHDQGDGXOWKRRGLVVWLOOXQNQRZQ

40

)LJ$QHFRORJLFDOIUDPHZRUNIRUDGROHVFHQWKHDOWKPRGL¿HGIURP$GDPVHWDO %OXPHWDO 

Genetic factors

Individual factors: age, gender, lifestyle/ health behaviour

LBP

Psychosocial factors

Physical determinants and environmental influences

Fig. 2. Risk factors of LBP symptoms: the individuals with accumulating factors are at DVXEVWDQWLDOULVNIRU/%3PRGL¿HGIURP$GDPVHWDO 

41

42

3

Purpose of the study

The main purpose of this study was to analyse the associations of a set of mainly PRGL¿DEOH SRWHQWLDO ULVN IDFWRUV ZLWK /%3 V\PSWRPV LQ D FRKRUW RI )LQQLVK DGROHVFHQWV 7KH IDFWRUV HYDOXDWHG ZHUH RYHUZHLJKW VPRNLQJ ZRUNORDG socioeconomic status, and the possible clustering of psychosocial and lifestyle factors. Moreover, we evaluated whether the possible association of these factors GLIIHUHGDW\HDUVGHSHQGLQJRQSUHYLRXV/%3V\PSWRPVDW\HDUV 7KHVWXG\TXHVWLRQVZHUHIRUPXODWHGDVIROORZV 1. Is persistent overweight and obesity, measured by BMI and WC, associated ZLWK/%3LQWKHIROORZXS" 2. ,VWKHDPRXQWDQGOHQJWKRIVPRNLQJKLVWRU\DVVRFLDWHGZLWK/%3LQWKHIROORZ XS" 3. 'RHVWKHGXUDWLRQRIZRUNORDGH[SRVXUHRUDVSHFL¿FW\SHRISK\VLFDOZRUNORDG IDFWRULQGLYLGXDOO\RULQFRPELQDWLRQDVVRFLDWHZLWK/%3LQWKHIROORZXS"  ,VVRFLRHFRQRPLFVWDWXVRIWKHIDPLO\DVVRFLDWHGZLWK/%3RIDGROHVFHQWV" 5. 'RHVDFFXPXODWLRQRISV\FKRVRFLDODQGOLIHVW\OHIDFWRUVDW\HDUVDVVRFLDWH ZLWK/%3DW\HDUVFURVVVHFWLRQDODQDO\VHV RUZLWKQHZ/%3LQWKHIROORZ XS"

43

44

4

Material and methods

4.1

Study design and population

7KH VWXG\ SRSXODWLRQ ZDV GUDZQ IURP WKH  1RUWKHUQ )LQODQG %LUWK &RKRUW 1)%& EDVHGRQOLYHERUQFKLOGUHQZLWKDQH[SHFWHGGDWHRIELUWKEHWZHHQ VW-XO\DQGWK-XQHQ  LQWKHWZRQRUWKHUQPRVWSURYLQFHV LQ)LQODQG2XOXDQG/DSODQG -lUYHOLQ et al. 1993). Data were collected during SUHJQDQF\DQGWKHFKLOGUHQZHUHDIWHUZDUGVIROORZHGXSDWWKHDJHVRI±PRQWKV \HDUVDQG\HDUV%HWZHHQ0D\DQG$SULO\HDUIROORZXS  DTXHVWLRQQDLUHUHJDUGLQJOLIHIULHQGVIDPLO\DQGVFKRRO KHDOWKPXVFXORVNHOHWDO symptoms, lifestyle factors and psychological symptoms was delivered to living PHPEHUVRIWKHFRKRUWZKRVHDGGUHVVHVZHUHNQRZQQ  2IWKHVXEMHFWV  UHVSRQGHG DQG  Q    DQVZHUHG WKH TXHVWLRQQDLUH DQG DJUHHG WR SDUWLFLSDWH $GGLWLRQDOO\ WKHLU SDUHQWV ZHUH DVNHG DERXW WKH VRFLRHFRQRPLF VLWXDWLRQRIWKHIDPLO\$W\HDUVQ  RIWKHSRSXODWLRQWRRNSDUWLQ a health examination. 7KH FXUUHQW VWXG\ SRSXODWLRQ 2%6  UHSUHVHQWV D VXEFRKRUW Q   RI 1)%&OLYLQJZLWKLQNPRIWKHFLW\RI2XOX7KH2%6VXUYH\GDWDZHUH FROOHFWHGEHWZHHQ6HSWHPEHUDQG-XQHZKHQWKHFRKRUWPHPEHUVZHUH DSSUR[LPDWHO\\HDUVROG\HDUIROORZXS 2IWKHVXEMHFWVUHVSRQGHG UHVSRQVH UDWH   DQG    DJUHHG WR SDUWLFLSDWH 7KH RQO\ H[FOXVLRQ FULWHULRQ ZDV SUHYLRXV ZRUN LQ 6WXG\ ,,, WKUHH VXEMHFWV ZKR ZHUH HPSOR\HG DW  \HDUV DQG KDG XQVSHFL¿HG SUHYLRXV ZRUN H[SRVXUH ZHUH H[FOXGHG 7KH TXHVWLRQQDLUHLQFOXGHGTXHVWLRQVRQWKHLUOLIHKHDOWKPXVFXORVNHOHWDOV\PSWRPV leisure time activities, occupational exposure, health behaviour, and psychological IDFWRUV$OO WKRVH ZKR UHVSRQGHG ZHUH LQYLWHG WR D FOLQLFDO H[DPLQDWLRQ DW 2XOX 'HDFRQHVV ,QVWLWXWH EHWZHHQ VXPPHU  DQG ZLQWHU  \HDU IROORZXS  ZKLFKLQFOXGHGPHDVXUHPHQWVRIZHLJKW:&DQGKHLJKWSDUWLFLSDWHG DQGUHVSRQGHGWRTXHVWLRQVRQPXVFXORVNHOHWDOV\PSWRPV In conclusion, the present study was a population-based prospective adolescent FRKRUWVWXG\2QH¿IWKRIWKHELUWKFRKRUWSRSXODWLRQGLGQRWUHVSRQGWRWKH\HDU EDVHOLQH TXHVWLRQQDLUH DQG RQHWKLUG RI WKH 2%6 FRKRUW VXEMHFWV LQ WKH \HDU IROORZXSVXUYH\ZHUHQRQUHVSRQGHUV7KHÀRZFKDUWRIWKHVWXGLHVLVSUHVHQWHG LQ)LJ

45

Northern Finland Birth Cohort (NFBC) 1985-86 n = 9,479

7-year questionnaire 1992–93 For parents of cohort members n = 9,326 (response rate 92%)

16-year questionnaire and health examination 2001-02 For all NFBC members n = 7,344 (response rate 80%) and n = 6,866 parents responded to a questionnaire for them

: NFBC NFBC members living within 100 km from Oulu n = 2,951 addresses known

from

2003-04 For all OBS members n = 1,987 (response rate 67%)

Clinical subcohort of OBS: 19-year questionnaire and physical examination 2005–06 n = 874 (44% of the OBS population)

Fig. 3. Flow chart of the study population.

4.2

Study ethics

The research protocol was designed and performed to adhere to the principles of :0$ WKH:RUOG 0HGLFDO$VVRFLDWLRQ  'HFODUDWLRQ RI +HOVLQNL$OO SDUWLFLSDQWV SURYLGHG LQIRUPHG ZULWWHQ FRQVHQW DQG WKH \HDU VXUYH\ DOVR LQFOXGHG DQ informed consent to be signed by their parents. Participation was voluntary and subjects were informed of the possibility to interrupt their participation whenever they wanted. Personal information was replaced by ID codes and the data were handled on group level only. The study was approved by the Ethics Committee of the University Hospital of Oulu. 4.3

Representativeness of the population

$WWKH2%6VXUYH\WKH¿QDOUHVSRQVHUDWHZDVFRQVLVWLQJRISDUWLFLSDQWV RXWRIHOLJLEOHRQHVRIWKHPZHUHER\VDQGJLUOV*LUOVUHVSRQGHG PRUHRIWHQWKDQER\Vvs. 7KHSDUWLFLSDQWVDQGQRQUHVSRQGHQWVGLGQRW 46

GLIIHUZLWKUHVSHFWWR/%3DWDQ\WLPHSRLQW7KHSDUWLFLSDQWVOLYHGDW\HDUVLQ WZRSDUHQWIDPLOLHVPRUHRIWHQWKDQWKHQRQUHVSRQGHQWVvs.RIER\V vs.RIJLUOV $GGLWLRQDOO\WKHSDUWLFLSDWLQJJLUOVZHUHVOLJKWO\VOLPPHU (the measured mean BMI 21.1 vs.  NJPð  DQG PRUH OLNHO\ QRQVPRNHUV  vs.   WKDQ QRQUHVSRQGHQWV DW  \HDUV7KH SDUWLFLSDQWV ZHUH VOLJKWO\ VOLPPHU SK\VLFDOO\ PRUH DFWLYH DQG PRUH OLNHO\ QRQVPRNHUV DW  \HDUV WKDQ QRQUHVSRQGHQWVEXWWKHGLIIHUHQFHVZHUHQRWVWDWLVWLFDOO\VLJQL¿FDQW $WWKH\HDUIROORZXSVWXG\, WKHSRSXODWLRQRIWKHVXEFRKRUWZDV VXEMHFWV RXW RI  HOLJLEOH RQHV  RI WKH SRSXODWLRQ   RI WKHP ZHUH ER\VDQGJLUOV7KHUHVSRQVHUDWHRIWKHER\VZDVDQGRIWKHJLUOV :KHQ DQDO\VLQJ JLUOV DQG ER\V VHSDUDWHO\ WKHUH ZHUH QR VWDWLVWLFDOO\ VLJQL¿FDQW GLVFUHSDQFLHV EHWZHHQ SDUWLFLSDQWV DQG QRQUHVSRQGHQWV $W  \HDUV WKH participating boys at the 19-year assessment reported slightly more often LBP and WKHSDUWLFLSDQWVJLUOVDQGER\V ZHUHDOVRVOLJKWO\VOLPPHUDQGPRUHOLNHO\QRQ VPRNHUV ,QFRQFOXVLRQWKHVXEMHFWVLQWKH¿QDOVWXG\SRSXODWLRQZHUHPRUHOLNHO\WREH living in families with two parents than the non-participants, but otherwise there ZHUHQRVLJQL¿FDQWGLIIHUHQFHVEHWZHHQWKHP 4.4

Assessment of low back pain

/%3ZDVDVVHVVHGDWDQG\HDUVZLWKWKHTXHVWLRQ³+DYH\RXKDGDQ\ SDLQRUDFKHLQ\RXUORZEDFNDUHDGXULQJWKHSDVWPRQWKV"´7KHUHVSRQVHRSWLRQV ZHUH³1R´³
RIWKHVWXG\DQGWKHWHUP³LQFLGHQFH´XVHGLQWKLVWKHVLVLVQRWV\QRQ\PRXVZLWK WKH HSLGHPLRORJLFDO GH¿QLWLRQ RI LQFLGHQFH:H XVHG WKH H[SUHVVLRQ ³QHZ /%3´ LQVWHDGRI³LQFLGHQW/%3´LQVWXG\,9LQRUGHUWRDYRLGPLVXQGHUVWDQGLQJV%\WKH GH¿QLWLRQ RI WKH SUHVHQW VWXG\ ³SHUVLVWHQW FDVHV´ ZHUH WKRVH ZKR UHSRUWHG /%3 ERWKDW\HDUVDQGDWIROORZXS6LPLODUO\ZHZDQWWRHPSKDVL]HWKDWWKHWHUP ³SHUVLVWHQW´LVQRWLGHQWLFDOWRFKURQLF/%3LQWKLVFRQWH[W

Fig. 4. LBP manikin used in the study.

4.5

Explanatory variables

4.5.1 Lifestyle factors 7KLVVWXG\LQFOXGHGGDWDRQZHLJKWUHODWHGPHDVXUHPHQWVVPRNLQJOHYHORIOHLVXUH WLPHSK\VLFDODFWLYLW\VHGHQWDU\EHKDYLRXUDQGVOHHSLQJDVSRWHQWLDOO\PRGL¿DEOH lifestyle factors of LBP.

48

Weight-related factors 7KHGDWDRQZHLJKWUHODWHGIDFWRUVZHUHLQTXLUHGDWIRXUWLPHSRLQWV:HLJKWDQG KHLJKW ZHUH UHSRUWHG E\ SDUHQWV DW VHYHQ \HDUV DQG E\ DGROHVFHQWV DW  \HDUV 7KH\ZHUHPHDVXUHGDWWKHDQG\HDUVXUYH\VXVLQJFDOLEUDWHGLQVWUXPHQWV according to the precise instructions given in the study protocol. BMI was calculated DV WKH ZHLJKW LQ NLORJUDPV GLYLGHG E\ WKH VTXDUH RI KHLJKW LQ PHWUHV NJPð  WR DQ DFFXUDF\ RI  NJ PHDVXUHG   NJ VHOIUHSRUWHG  DQG  FP PHDVXUHG  1 cm (self-reported), respectively. Self-reported data, if available, were used for WKRVHZKRGLGQRWSDUWLFLSDWHLQWKHPHDVXUHPHQWVDQGDGROHVFHQWVZHUHDVNHGWR report the exact date of the measurement. In the analyses of BMI, we used Cole’s international criteria for measuring childhood obesity, which provides age- and sexVSHFL¿FFXWRIISRLQWVIRURYHUZHLJKWDQGREHVLW\DPRQJFKLOGUHQEHWZHHQDQG years of age (Cole et al. $W\HDUVQRUPDOZHLJKWZDVGH¿QHGDV NJPDPRQJER\VDQGNJPDPRQJJLUOVRYHUZHLJKWDV±NJ PDPRQJER\VDQG±NJPDPRQJJLUOVDQGREHVLW\DV!NJ P DPRQJ ER\V DQG ! NJP DPRQJ JLUOV %0, ZDV XVHG DV D FRQWLQXRXV YDULDEOHLQVWXG\,9+HLNNDODet al.  :&ZDVPHDVXUHGDWDQG\HDUVLQKHDOWKH[DPLQDWLRQVZLWKWKHVDPH ¿[HG SURFHGXUH KRUL]RQWDOO\ DW KDOIZD\ EHWZHHQ WKH LOLDF FUHVW DQG WKH ORZHVW rib while lightly exhaling with an accuracy of 0.5 cm. Pregnant girls were not measured. Smoking 'DWD RQ VPRNLQJ ZHUH LQTXLUHG DW  DQG  \HDUV ZLWK WKH TXHVWLRQV ³+DYH \RX HYHU VPRNHG"´ ³+DYH \RX HYHU VPRNHG UHJXODUO\ LQ \RXU OLIH"´ ³$W ZKDW DJH GLG \RX VWDUW VPRNLQJ"´ ³+RZ PDQ\ \HDUV KDYH \RX VPRNHG"´ ³$UH \RX VPRNLQJQRZDGD\V"´DQG³+RZPXFKGR\RXVPRNHFLJDUHWWHVSHUGD\ "´7KH UHVSRQVHRSWLRQVWRWKHTXHVWLRQFRQFHUQLQJFXUUHQWVPRNLQJZHUH QRWDWDOO  FDVXDOO\ RQFHDZHHN ±GD\VDZHHN ±GD\VDZHHNDQG  GD\VDZHHN6PRNHUVZHUHGH¿QHGDVWKRVHZKRVPRNHGUHJXODUO\±GZN DQG QRQVPRNHUVDVWKRVHZKRGLGQRWVPRNHDWDOORUZKRVPRNHGRFFDVLRQDOO\VWXG\ ,±,,, $FFXPXODWHG SDFN\HDUV ZHUH FDOFXODWHG  SDFN\HDU LV HTXLYDOHQW WR  FLJDUHWWHVVPRNHGSHUGD\GXULQJRQH\HDU EDVHGRQWKHLQIRUPDWLRQRQUHJXODUO\ VPRNHG\HDUVDQGWKHDPRXQWRIFLJDUHWWHVVPRNHGSHUGD\7KHH[SRVXUHE\SDFN \HDUVZDVFDWHJRUL]HGDV±DQGRYHUDW\HDUVVWXG\,, DQGDVQRQ 49

UHJXODUVPRNHU±SDFN\HDUVDQGRYHUSDFN\HDUVDW\HDUVVWXG\,9  Some individual outliers indicating faulty data were corrected to the subgroup over FLJDUHWWHVSHUGD\IRUH[DPSOHFLJDUHWWHVSHUGD\  Leisure time physical activity $GROHVFHQWVZHUHLQTXLUHGDERXWWKHLUOHYHORISK\VLFDODFWLYLW\DW\HDUV7KH\ ZHUHDVNHG ³+RZPXFKGR\RXSDUWLFLSDWHLQEULVNSK\VLFDODFWLYLW\RXWVLGH VFKRRO KRXUV"´ DQG   ³+RZ RIWHQ GR \RX SDUWLFLSDWH LQ EULVN SK\VLFDO DFWLYLW\ RXWVLGH VFKRRO KRXUV IRU DW OHDVW  PLQXWHV DW D WLPH"´ %ULVN SK\VLFDO DFWLYLW\ ZDVGH¿QHGDVSK\VLFDODFWLYLW\FDXVLQJDWOHDVWVRPHVZHDWLQJDQGVKRUWQHVVRI EUHDWKZKLFKKDVEHHQGH¿QHGDVPRGHUDWHWRYLJRURXVSK\VLFDODFWLYLW\093$  (Tammelin et al. 7KHUHVSRQVHRSWLRQVWRWKH¿UVWTXHVWLRQZHUH QRWDW DOO DERXWòKSHUZHHN DERXWKSHUZHHN ±KSHUZHHN DERXW ±KSHUZHHNDQG •KSHUZHHN7KHUHVSRQVHRSWLRQVWRWKHVHFRQGTXHVWLRQ ZHUH QHYHU ”RQFHDPRQWK ±WLPHVSHUPRQWK RQFHDZHHN   WZLFH D ZHHN    WLPHV D ZHHN   ± WLPHV D ZHHN DQG   GDLO\7KH IUHTXHQF\RISK\VLFDODFWLYLW\ZDVFODVVL¿HGLQWRIRXUFDWHJRULHVRQFHDPRQWKRU OHVVRIWHQPRUHWKDQRQFHDPRQWKEXWOHVVWKDQWZLFHDZHHNRUWLPHVDZHHN DQGRYHUWLPHVDZHHNVWXG\,±,,, 3K\VLFDODFWLYLW\E\WLPHVSHQWZDVFODVVL¿HG DVDFWLYH!KRXUVRI093$SHUZHHN PRGHUDWHO\DFWLYHWRKRXUVRI093$ SHUZHHN DQGLQDFWLYHKRXU093$SHUZHHN VWXG\,9 7HVWUHWHVWUHOLDELOLW\ RI WKH PHDVXUHPHQW ZDV HYDOXDWHG LQ D VXEJURXS RI  DGROHVFHQWV ZKLFK ZDV LQYLWHGIRU¿WQHVVWHVWVWKHLQWUDFODVVFRUUHODWLRQFRHI¿FLHQWZDV7DPPHOLQ et al.  Leisure time sedentary behaviour /HLVXUHWLPHDPRXQWRIVLWWLQJZDVHYDOXDWHGDW\HDUVEDVHGRQVHOIUHSRUWVRI GLIIHUHQWVHGHQWDU\EHKDYLRXUV7KHDYHUDJHVLWWLQJWLPHSHUGD\KGD\LVVXH ZDV DVVHVVHG E\ DVNLQJ SDUWLFLSDWLRQ LQ IRXU GLIIHUHQW VHGHQWDU\ DFWLYLWLHV ZDWFKLQJ WHOHYLVLRQ UHDGLQJ ERRNV RU PDJD]LQHV SOD\LQJ RU ZRUNLQJ RQ D FRPSXWHU DQG other sedentary activities) outside school hours. The reported sedentary hours per GD\ZHUHVXPPHGXSDQGFDWHJRUL]HGDVKRXUVRUOHVVSHUGD\±KRXUVDQG hours or more per day for boys (Tammelin et al. DQGFRQWLQXRXVYDULDEOHZDV used for girls (study IV). Test-retest reliability of the measurement was evaluated DQGLQWUDFODVVFRUUHODWLRQFRHI¿FLHQWZDV7DPPHOLQet al.  50

Quantity of sleep 7KHDYHUDJHVOHHSLQJWLPHDW\HDUVZDVLQTXLUHGZLWKWKHTXHVWLRQ³+RZPDQ\ KRXUVRQDYHUDJHGR\RXVOHHSSHUGD\"´,WZDVFODVVL¿HGDVOHVVWKDQKRXUV to 9 hours, and more than 9 hours per day (study IV). The sleep recommendations IDYRXUDVOHHSLQJWLPHIURPWRKRXUVLQWKLVDJHJURXSDQGLWZDVUHJDUGHGDV optimal (Matricciani et al. 2012). 4.5.2 Physical workload 3K\VLFDO ZRUNORDG ZDV FRQVLGHUHG DV D SRWHQWLDOO\ PRGL¿DEOH HQYLURQPHQWDO ULVN IDFWRU RI /%3 VWXG\ ,,,  7KH OLVW RI LQFOXGHG H[SRVXUHV LV D FRQVHQVXV RI WHDPZRUN LW ZDV EDVHG RQ SUHYLRXV VWXGLHV FRQGXFWHG DPRQJ DGXOWV DQG PDQ\ H[SHUWV ZHUH FRQVXOWHG 'DWD RQ SUHYLRXV ZRUN KLVWRU\ ZHUH DVVHVVHG ZLWK WKH \HDU TXHVWLRQQDLUH )RU WKH HYDOXDWLRQ RI WKH PDLQ DFWLYLW\ WKH VXEMHFWV ZHUH HQTXLUHG WR DQVZHU 1R RU
VWUHVVRQWKHOXPEDUVSLQH3UHYLRXVO\WKH\KDYHEHHQFRQVLGHUHGDVSRWHQWLDOULVN IDFWRUVIRUPXVFXORVNHOHWDOGLVHDVHVUHODWHGWRZRUNORDG%DNNHU et al. 2009). The VSHFL¿FDYHUDJHRIWKHVHH[SRVXUHVZDVDVNHGIRUWKHFXUUHQWMREDQGWKHORQJHVW previous job held for at least 12 months and the longest job of jobs held for less WKDQPRQWKV7KHUHVSRQVHRSWLRQVZHUH³1R´DQG³
time of the current study. Depressive mood may be associated with pain symptoms (Bair et al. DVZHOODVVPRNLQJ6LKYRODet al. DQGLWZDVFRQVLGHUHGDV a confounder in study II. Emotional and behavioural problems
53

4.5.4 Other measurements 6HOIUHODWHGVWDWHRIKHDOWKZDVDVNHGDW\HDUVZLWKWKHTXHVWLRQ³+RZZRXOG \RXGHVFULEH\RXUKHDOWKDWWKHPRPHQW"´,WZDVFDWHJRUL]HGDVSRRURUYHU\SRRU JRRGDQGYHU\JRRG7KHDGROHVFHQWVZHUHDVNHGDW\HDUVWRGH¿QHWKHSHUVRQV with whom they were mainly living to get a picture of their family type. The FODVVL¿FDWLRQVRIVHOIUHODWHGKHDOWKDQGW\SHRIIDPLO\ZHUHXVHGIRUWKHDQDO\VHV of the representativeness of the subsamples of the population. 

6WDWLVWLFDOPHWKRGV

The characteristics of participants and non-responders were compared with WKH 3HDUVRQ Ȥ DQG 6WXGHQW t test. The associations between LBP and possible FRQIRXQGHUVZHUHDQDO\VHGE\FURVVWDEXODWLRQDQGWKHFKLVTXDUHWHVWDWDQG  \HDUV &URVVWDEXODWLRQV ZHUH DOVR XVHG WR HYDOXDWH WKH GHVFULSWLYH GDWD RQ study population. We tested the gender differences in dependent and independent YDULDEOHVXVLQJ3HDUVRQ¶VFKLVTXDUHWHVW$VJHQGHUGLIIHUHQFHVZHUHIRXQGLQWKH H[SODQDWRU\ IDFWRUV RI /%3 DV ZHOO DV LQ WKH SUHYDOHQFH RI /%3 ZH VWUDWL¿HG a priori the analyses by gender. When a disease is common, meaning that its incidence is more than 10%, the ORJLVWLFUHJUHVVLRQRYHUVWDWHVWKHDGMXVWHGUHODWLYHULVNDQGWKHORJELQRPLDOPRGHO has been preferred (McNutt et al. 2003). The log-binomial model, in general, produces an unbiased estimate, but some problems may appear, for example if adjustment is made for many confounders (McNutt et al. 2003). In this study, the associations between explanatory factors and LBP were analysed with log-binomial UHJUHVVLRQPRGHOZLWKDGMXVWPHQWIRUFRQIRXQGHUVDQGVWUDWL¿HGE\JHQGHUH[FHSW IRU WKH FKURQRORJLFDOO\ ¿UVW VWXG\ ,, ZKLFK XVHG ORJLVWLF UHJUHVVLRQ PRGHO$OO DQDO\VHVZHUHSHUIRUPHGVWUDWL¿HGE\WKHSUHVHQFHRI/%3DW\HDUVQR/%3YV DQ\/%3DW\HDUV  4.6.1 The area under the curve (AUC) method :HXVHGWKHDUHDXQGHUWKH%0,YVWLPHFXUYH$8& IRUUHÀHFWLQJWKHWRWDOORDGRI ERG\PDVVRQWKHVSLQH%0,DVWKHSUR[\VHSDUDWHO\IURPWR\HDUVDQGIURP WR\HDUV$OWPDQ/DLWLQHQet al. 6LPLODUO\WKH$8&PHWKRGZDV XVHGLQUHÀHFWLQJWKHWRWDOORDGRI:&IURPWR\HDUV$8&PDWKHPDWLFDOO\ NQRZQDVDGH¿QLWHLQWHJUDOLVXVXDOO\XVHGIRUUHSHDWHGPHDVXUHPHQWVLQVWHDGRI 54

mean values to present cumulative amount of change over time, especially when timeframes are uneven or in the case of missing measurements (Sarna 2012). The $8&RI%0,DQG:&KDGDVNHZHGGLVWULEXWLRQDQGZHSHUIRUPHGORJDULWKPLF transformations which were scaled for each other’s standard deviation. 4.6.2 Latent Class Analyses (LCA) /DWHQW &ODVV$QDO\VLV /&$  LV D VWDWLVWLFDO WHFKQLTXH WR VHHN XQFRYHUHG JURXSV of participants. In latent models, the distribution of individuals into meaningful subgroups is based on probabilities, and no assumptions of linear relationships, QRUPDO GLVWULEXWLRQV RU KRPRJHQHLW\ DUH UHTXLUHG 0DJLGVRQ 9HUPXQW   ,QWKLVVWXG\/&$ZDVXVHGIRUWZRSXUSRVHV)LUVWLWZDVXVHGWRREWDLQQDWXUDO clusters, i.e. JURXSV LQ ZKLFK WKH LQGLYLGXDOV KDG VLPLODU ZRUNORDG SUR¿OHV %DUWKRORPHZ  .QRWW  0DJLGVRQ  9HUPRQW   6HYHQ ZRUNORDG exposures were selected as a potential cause of additional biomechanical stress on WKHOXPEDUVSLQHDQGRQWKHEDVLVRISUHYLRXVOLWHUDWXUH%DNNHUet al. $OO these exposures during the evaluated two-year period were included, whether they KDG RFFXUUHG VLPXOWDQHRXVO\ RU DW GLIIHUHQW WLPH SRLQWV 8VLQJ WKH /&$ PHWKRG with conditional independence assumption and Bayes’ theorem each individual’s a posteriori probability in each class was calculated and he or she was then assigned to the latent class cluster with the highest a posteriori probability. The number RIFOXVWHUVZDVGHWHUPLQHGZLWKWZRVWDWLVWLFDOGLDJQRVWLFV%D\HVLDQ,QIRUPDWLRQ &ULWHULRQ %,&  DQG WKH 9XRQJ/R0HQGHOO5XELQ /LNHOLKRRG 5DWLR 7HVW /57  0XWKpQ  0XWKpQ  1\OXQG et al.   $FFRUGLQJ WR UHFHQW VLPXODWLRQ studies the model with the lowest value of BIC is the one to be preferred (Nylund et al. ,QWKH/57VWDWLVWLFVDORZSYDOXH LQGLFDWHVWKDWWKHTXDOL¿HG PRGHO¿WVWKHXVHGGDWDEHWWHUWKDQWKHPRGHOZLWKRQHOHVVFOXVWHU7KHQXPEHURI FOXVWHUVZDV¿UVWGHWHUPLQHGEDVHGRQ/57PD[LPXPFOXVWHUV DQGWKHQFKHFNHG for compatibility with the BIC measure. 6HFRQG/&$ZDVXVHGWRREWDLQFOXVWHUVLQZKLFKWKHLQGLYLGXDOVKDGDVLPLODU SUR¿OHRILQFOXGHGOLIHVW\OHDQGSV\FKRVRFLDOULVNIDFWRUV7KHVHOHFWLRQRIIDFWRUV LQFOXGHGZDVPDGHEDVHGRQDOOSUHYLRXVO\SXEOLVKHG1)%&DQG2%6VWXGLHVRQ PXVFXORVNHOHWDOSUREOHPVDQG/%37KHIDFWRUVXVHGIRUGHVFULELQJOLIHVW\OHDW \HDUVZHUHOHLVXUHWLPHSK\VLFDODFWLYLW\VOHHSLQJVPRNLQJVHGHQWDU\EHKDYLRXU RYHUZHLJKWREHVLW\ZKHUHDVLQWHUQDOL]LQJDQGH[WHUQDOL]LQJV\QGURPHVZHUHXVHG IRUSV\FKRORJLFDOV\PSWRPV)LUVWZHWULHGWRFRQVLGHUDOOYDULDEOHVDVFRQWLQXRXV LQ WKH /&$ PRGHO EXW WKH JURXS VL]HV ZHUH WRR VPDOO +HLNNDOD et al.   55

6HFRQG ZH WULHG RXW GLIIHUHQW FRPELQDWLRQV )LQDOO\ ZH VHOHFWHG %0, DPRQJ both genders and sedentary activity among girls as continuous variables. Leisure WLPHSK\VLFDODFWLYLW\VOHHSLQJDQGVPRNLQJDPRQJERWKJHQGHUVDQGVHGHQWDU\ activity among boys were divided into three categories on the basis of previous VWXGLHV DQG UHFRPPHQGDWLRQV +HLNNDOD et al.   :H DVVHVVHG PRGHOV ZLWK RQHWRVHYHQFOXVWHUV7RGHWHUPLQHWKHEHVW¿WWLQJFOXVWHUVROXWLRQRIWKHFDQGLGDWH PRGHOV$NDLNH LQIRUPDWLRQ FULWHULRQ $,&  %,& DQG WKH VDPSOHVL]H DGMXVWHG %,& 66$%,&  ZHUH FDOFXODWHG DQG XVHG WR PHDVXUH JRRGQHVVRI¿W$FFRUGLQJ WRWKHFULWHULDRIWKHVHVWDWLVWLFDO¿WLQGLFHVWKHORZHUWKHYDOXHVWKHEHWWHUPRGHO ¿W WKH\ LQGLFDWH 9HUPXQW  0DJLGVRQ   7KH /57 DYHUDJH ODWHQW FODVV FODVVL¿FDWLRQDFFXUDF\DQGHQWURS\PHDVXUHVZHUHXVHGDGGLWLRQDOO\WRLGHQWLI\WKH RSWLPDOQXPEHURIWKHFOXVWHUV+HLNNDOD et al. 9HUPXQW 0DJLGVRQ  $IWHUGHWHUPLQDWLRQRIWKHQXPEHURIFOXVWHUVWKHHQWURS\PHDVXUHVXQFHUWDLQW\LQ WKHFODVVL¿FDWLRQYDOXHVUDQJLQJIURPWR  4.6.3 Description of the individual studies ,QVWXG\,ZHXVHG$8&RI%0,DQG:&WRUHYHDOLISHUVLVWHQWRYHUZHLJKWDQG REHVLW\DUHUHODWHGZLWK³LQFLGHQW´RU³SHUVLVWHQW´/%3DPRQJFRKRUWPHPEHUVDV studies among adult populations have proposed (Shiri et al. 2010a). The associations between BMI, WC and LBP were analysed by the log-binominal regression model. 5HODWLYHULVNV55 DQGWKHLUFRQ¿GHQFHLQWHUYDOV&, ZHUH¿UVWDGMXVWHG IRUVPRNLQJQRQVPRNHUVDVUHIHUHQFH DQGOHLVXUHWLPHSK\VLFDODFWLYLW\WZRRU WKUHHWLPHVDZHHNDVUHIHUHQFH DWWKHDJHRI\HDUV6HFRQGZHDOORZHGIRUWKH family socioeconomic status (upper-level administrative as reference). ,QVWXG\,,VPRNLQJZDVFRQVLGHUHGDVDSRVVLEOHSUHGLFWRURI³LQFLGHQW´RU ³SHUVLVWHQW´/%3EDVHGRQWKHSUHYLRXVVWXGLHVDPRQJDGROHVFHQWV)HOGPDQet al. 1999) and young adults (Mustard et al. 7KHDVVRFLDWLRQEHWZHHQVPRNLQJ and LBP (Reporting LBP and Consultation for LBP combined) was analysed with logistic regression analysis with adjustments for the family socioeconomic status, leisure time physical activity, BMI, and self-related depressive mood. The DVVRFLDWLRQRIVPRNLQJZLWKWKUHHFDWHJRU\YDULDEOH/%3QR/%3vs. Reporting LBP or Consultation for LBP) was analysed in the total population (girls and boys combined) using multinomial regression analysis with adjustment for gender and the confounders. The odds ratios (OR) and their 95% CIs were calculated. Subject ZLWKRXW DQ\ /%3 DW  DQG  \HDUV ZHUH XVHG DV WKH UHIHUHQFH JURXS 5HJXODU VPRNHUVZHUHGH¿QHGDVDGROHVFHQWVVPRNLQJRQWRGD\VDZHHN 56

,QVWXG\,,,WKHDVVRFLDWLRQVEHWZHHQZRUNORDGYDULDEOHVDQG³LQFLGHQW´DQG ³SHUVLVWHQW´/%3ZHUHDQDO\VHGZLWKORJELQRPLDOUHJUHVVLRQDQDO\VLV5LVNUDWLRV 55  DQG WKHLU  &,V ZHUH DGMXVWHG IRU VPRNLQJ %0, OHLVXUH WLPH SK\VLFDO DFWLYLW\DQGWKHIDPLO\VRFLRHFRQRPLFVWDWXVDWWKHDJHRI\HDUV$GGLQJ%0, or socioeconomic status did not affect the results and they were removed from the ¿QDODQDO\VLV7KHGXUDWLRQRIZRUNH[SRVXUHPRQWKV KDGDVNHZHGGLVWULEXWLRQ and a logarithmic transformation was performed per a unit of standard deviation. 7KH DVVRFLDWLRQ EHWZHHQ ³LQFLGHQW´ DQG ³SHUVLVWHQW´ /%3 DQG /&$ FOXVWHUV RI ZRUNORDGIDFWRUVZDVLQYHVWLJDWHGXVLQJORJELQRPLDOUHJUHVVLRQDQDO\VLV$GMXVWHG ULVNUDWLRV55 DQGWKHLU&,VZHUHFDOFXODWHG7KHDQDO\VHVZHUHDGMXVWHGIRU VPRNLQJDQGOHLVXUHWLPHSK\VLFDODFWLYLW\ ,QVWXG\,9WKHRXWFRPHPHDVXUHVZHUHWKHRFFXUUHQFHRI/%3DW\HDUVDQG QHZ/%3FRUUHVSRQGLQJWR³LQFLGHQW/%3´LQSUHYLRXVVWXGLHV DW\HDUV7KH DVVRFLDWLRQVEHWZHHQ/&$FOXVWHUVRILQFOXGHGSV\FKRVRFLDODQGOLIHVW\OHIDFWRUV DW\HDUVDQG/%35HSRUWLQJ/%3DQG&RQVXOWDWLRQIRU/%3VHSDUDWHO\ ZHUH DQDO\VHGZLWKORJELQRPLDOUHJUHVVLRQDQDO\VLVDQGVWUDWL¿HGE\JHQGHU5HODWLYH ULVNV55 DQGWKHLU&,VZHUHDQDO\VHGDVVWUDWL¿HGE\WKHSUHVHQFHRI/%3DW \HDUV7KHLQFOXVLRQRIIDPLO\¶VVRFLRHFRQRPLFVWDWXVDVDFRQIRXQGHUGLGQRW DIIHFWWKHUHVXOWVDQGZDVUHPRYHGIURPWKH¿QDODQDO\VLV6SHDUPDQ¶VFRUUHODWLRQ ratios were used to analyse the possible co-linearity between inactivity and VHGHQWDU\OLIHVW\OHDVZHOODVEHWZHHQLQWHUQDOL]LQJDQGH[WHUQDOL]LQJV\QGURPHV In the unpublished study, the outcome measures were occurrence of LBP at \HDUV5HSRUWLQJ/%3DQG&RQVXOWDWLRQIRU/%3FRPELQHG DQG³LQFLGHQW´RU ³SHUVLVWHQW´/%3DW\HDUV5HSRUWLQJ/%3DQG&RQVXOWDWLRQIRU/%3FRPELQHG  In the evaluation of the possible association between family’s socioeconomic status and occurrence of LBP, RRs and their 95% CIs for LBP were examined E\ORJELQRPLDOUHJUHVVLRQXVLQJµQR/%3¶DVWKHUHIHUHQFH¿UVWE\XVLQJIDPLO\ socioeconomic status as an explanatory factor and then adding one by one BMI, VPRNLQJDQGOHLVXUHWLPHSK\VLFDODFWLYLW\WRWKHPRGHODVSRWHQWLDOFRQIRXQGHUV 7KHQ DVVRFLDWLRQ EHWZHHQ IDPLO\¶V VRFLRHFRQRPLF VWDWXV DQG ³LQFLGHQW´ DQG ³SHUVLVWHQW´ /%3 ZDV DQDO\VHG XVLQJ PXOWLQRPLDO ORJELQRPLDO UHJUHVVLRQ ZLWK DGMXVWPHQWIRUJHQGHU7KHPRVWFRPPRQJURXSZRUNHUV ZDVXVHGDVDUHIHUHQFH 7KH DQDO\VHV ZHUH FDUULHG RXW E\ XVLQJ 6$6 VRIWZDUH YHUVLRQ  6$6 ,QVWLWXWH,QF&DU\1&86$ 03OXV9HUVLRQDQG DQGWKH6366 VRIWZDUHIRU:LQGRZVYHUVLRQDQG6366,QF&KLFDJR,/ 

57

Table 5. Summary of the methods used in the thesis. Study I

II

Study setting Follow-up

Follow-up

Study population

Outcome

Explanatory

variable

variables

Covariates

OBS,

“Incident” and

BMI (7,16, and

Smoking, PHA,

subpopulation

“persistent” LBP

18 years) and

and SES at 16

(n = 786) at 19

at 18 and 19

WC (16 and 19

years

years

years

years)

OBS

”Incident” and

Smoking (16 and

BMI, PHA, SES,

”persistent” LBP

18 years)

and depressive mood at 16

at 18 years

years III

IV

Follow-up

OBS (n = 1,984)¹

”Incident” and

Working

Smoking, PHA,

”persistent” LBP

history, physical

(BMI, SES) at 16

at 18 years

workload factors

years

Cross-sectional

NFBC86 and

LBP at 16 years

Psychosocial

(SES at 16

and follow-up

OBS

and new LBP at

(externalizing

years)

18 years

and internalizing syndromes) and lifestyle factors (PHA, sleeping, smoking, sedentary behaviour, and BMI) SES

Smoking, BMI,

SES

Cross-sectional

NFBC86 and

LBP at 16 years

and

and follow-up

OBS

and “incident”

and PHA at 16

and “persistent”

years

LBP

LBP at 18 years ¹ Those three subjects, who were employed at 16 years, were excluded from the study. OBS, Oulu Back Study (n = 1,987); NFBC86, Northern Finland Birth Cohort 1986 (n = 6,968); BMI, body mass index; WC, waist circumference; PHA, leisure time physical activity; SES, family’s socioeconomic status. Boys and girls were analysed separately (except study II, which included also analyses of boys and girls combined).

58

5

Results

5.1

Characteristics of the study population

7KH ¿QDO VWXG\ SRSXODWLRQ WKH 2%6 VXEFRKRUW RI WKH 1)%&  SRSXODWLRQ FRQVLVWHG RI  DGROHVFHQWV  JLUOV DQG  ER\V  ZKR UHVSRQGHG WR D SRVWDOTXHVWLRQQDLUHDW\HDUVDQGJDYHWKHLUFRQVHQWWRWKHXVHRIWKHLUGDWD7KH DGGLWLRQDOFOLQLFDOVXEFRKRUWDW\HDUVFRQVLVWHGRIDGROHVFHQWVJLUOV  (study I). The descriptive information on lifestyle factors (leisure time physical DFWLYLW\VPRNLQJ%0,VHGHQWDU\EHKDYLRXUDQGVOHHSLQJ RIWKH2%6FRKRUWDW \HDUVLVSUHVHQWHGLQ7DEOH$JHQGHUGLIIHUHQFHZDVIRXQGLQSK\VLFDODFWLYLW\ %HLQJSK\VLFDOO\YHU\DFWLYHZDVPRUHFRPPRQDPRQJER\VWKDQJLUOVYV  +RZHYHUWKHUHZDVDOVRDJHQGHUGLIIHUHQFHLQVHGHQWDU\EHKDYLRXUUHYHDOLQJ that 32% of boys vs.RIJLUOVVDWPRUHWKDQKRXUVSHUGD\$GGLWLRQDOO\ER\V JRWKRXUVRIVOHHSPRUHRIWHQWKDQJLUOV 7KH GHVFULSWLYH LQIRUPDWLRQ RQ SV\FKRVRFLDO IDFWRUV DW  \HDUV LQ WKH 2%6 SRSXODWLRQLVSUHVHQWHGLQ7DEOH*LUOVUHSRUWHGHPRWLRQDOSUREOHPVPRUHRIWHQ WKDQER\VRIJLUOVvs.RIER\VKDGLQWHUQDOL]LQJSUREOHPVDQGRIJLUOV vs.RIER\VUHSRUWHGKDYLQJKDGGHSUHVVLYHPRRGGXULQJWKHSUHFHGLQJPRQWK SHULRG$ JHQGHU GLIIHUHQFH ZDV DOVR IRXQG LQ WKH EHKDYLRXUDO SUREOHPV DV JLUOV UHSRUWHGPRUHH[WHUQDOL]LQJSUREOHPVWKDQER\Vvs.  The descriptive information on BMI and WC at different ages in the OBS SRSXODWLRQ LV SUHVHQWHG LQ )LJ  WR  %0, DW  \HDUV ZDV FDSWXUHG IURP WKH SUHYLRXV1)%&GDWD7KHPHDQ%0,LQFUHDVHGZLWKWLPHDPRQJERWKJHQGHUV 7KHLQFUHDVHRI:&ZDVSURPLQHQWDPRQJER\VEHWZHHQDQG\HDUVPHDQ :&LQFUHDVHGDERXWFHQWLPHWUHV 7KHGLVWULEXWLRQRI$8&RI%0,IURPWR \HDUVLVSUHVHQWHGLQ)LJ $W WKH DJH RI  \HDUV HYHU\ IRXUWK DGROHVFHQW Q     KDG QHYHU VPRNHGZKLOHHYHU\IRXUWKVPRNHGUHJXODUO\Q  Q  ZHUH H[VPRNHUVQ  VPRNHGRQWRGD\VDZHHNDQGQ  VPRNHG RFFDVLRQDOO\7KHFXPXODWLYHDPRXQWRIVPRNLQJDW\HDUVZDV6'  SDFN\HDUV%R\VKDGVPRNHGVOLJKWO\PRUHWKDQJLUOV6' SDFN\HDUV vs.6' SDFN\HDUV  :RUNLQJKLVWRU\ZDVDVVHVVHGUHWURVSHFWLYHO\DWWKHDJHRI\HDUV'XULQJ WKHSUHYLRXV\HDUSHULRGJLUOV DQGER\V KDGEHHQZRUNLQJ  ZHUHHPSOR\HGLQIXOOWLPHMREV  ZHUHVWXG\LQJ 59

 ZHUHQRWZRUNLQJRUVWXG\LQJZKLOHGDWDDERXWWKHLUPDLQDFWLYLW\ZDVQRW DYDLODEOHIRUVXEMHFWV  7KH 1)%&  \HDU GDWD  FRKRUW PHPEHUV  ZDV XVHG IRU comprehensive cluster analyses of psychosocial and lifestyle factors as well as for FURVVVHFWLRQDODQDO\VHVRI/%3VWXG\,9 7KH¿QDOVWXG\SRSXODWLRQQ   FRQVLVWHGRIJLUOV DQG ER\VZLWKVXI¿FLHQWGDWD$GHWDLOHG GHVFULSWLRQRIWKHSV\FKRVRFLDODQGOLIHVW\OHIDFWRUVRI1)%&SDUWLFLSDQWVDQG the results of the cluster analyses are presented later. (TXDOO\ LQ WKH FURVVVHFWLRQDO VWXG\ RI IDPLO\¶V VRFLRHFRQRPLF VWDWXV DQG DGROHVFHQWV /%3 WKH 1)%&  \HDU GDWD ZDV XVHG %DVHG RQ WKH GDWD RQ DGROHVFHQWVIDWKHU¶VUHVSRQVHZDVXVHGLQ RIIDPLOLHVUHSRUWHG EHORQJLQJWRKLJKHUFOHULFDOHPSOR\HHVZHUHVHOIHPSOR\HGZHUHORZHU FOHULFDOHPSOR\HHVZHUHZRUNHUVDQGUHSRUWHGVRPHWKLQJHOVHVWXGHQWV VHQLRUVXQHPSOR\HGRUXQNQRZQ 

60

7DEOH'HVFULSWLYHLQIRUPDWLRQRQOLIHVW\OHIDFWRUVDPRQJJLUOVDQGER\VRIWKH2XOX %DFN6WXG\2%6 DW\HDUV Lifestyle factors

Girls

Boys

Total

n = 1079 (%)

n = 908 (%)

n = 1987 (%)

(n = 957)

(n = 780)

(n = 1755)

”2QFHDPRQWK

139 (14)

105 (14)

244 (14)

!2QFHDPRQWKEXW”2QFHDZHHN

249 (26)

153 (20)

402 (23)

2 or 3 times a week

332 (34)

223 (29)

555 (32) 554 (32)

Frequency of leisure time physical

r2 test

p < 0.001

activity

•WLPHVDZHHN

255 (26)

299 (38)

(n = 969)

(n = 775)

(n = 1744)

Have never smoked

345 (36)

276 (36)

621 (36)

Ex-smokers

271 (28)

273 (35)

544 (31)

Occasional smokers

159 (16)

101 (13)

260 (15)

Smokes 1–4 d/week

45 (5)

24 (3)

69 (4)

Regular smokers (5–7 d/week)

149 (15)

101 (13)

250 (14)

Smoking: pack-years¹

(n = 951)

(n = 756)

(n = 1707)

Non-regular smoker

785 (83)

646 (85)

1431 (84)

0.1–1.0 pack-years

110 (12)

60 (8)

170 (10)

> 1.0 pack-years

56 (6)

50 (7)

106 (6)

(n = 1007)

(n = 830)

(n = 1837)

Smoking

Body mass index

p = 0.005

p = 0.042

p = 0.088

(kg/m², Cole’s criteria) Underweight

105 (10)

65 (8)

170 (9)

Normal weight

777 (77)

636 (77)

1413 (77)

Overweight

95 (9)

98 (12)

193 (11)

Obese

30 (3)

31 (4)

61 (3)

(n = 949)

(n = 755)

(n = 1704)

”KRXUVGD\

312 (33)

179 (24)

491 (29)

4.1–7.9 hours/day

399 (42)

336 (45)

735 (43)

•KRXUVGD\

238 (25)

240 (32)

478 (28)

(n = 950)

(n = 750)

(n = 1700)

< 8 hours/day

225 (24)

131 (18)

356 (21)

8–9 hours/day

625 (66)

502 (67)

1127 (66)

> 9 hours/day

100 (11)

117 (16)

217 (13)

Amount of leisure time sitting

Sleeping time

p < 0.001

p < 0.001

¹ Accumulated pack-years by the age of 16 (one pack-year = 15 cigarettes smoked per day for a year).

61

7DEOH'HVFULSWLYHLQIRUPDWLRQRISV\FKRVRFLDOIDFWRUVDPRQJJLUOVDQGER\VRIWKH 2XOX%DFN6WXG\2%6 DW\HDUV Psychosocial factors

Girls

Boys

Total

n = 1079 (%)

n = 908 (%)

n = 1987 (%)

Family socioeconomic status

(n = 906)

(n = 768)

(n = 1674)

Higher clerical employees

263 (29)

245 (32)

508 (30)

Self-employed

92 (10)

76 (10)

168 (10)

Lower clerical employees

186 (21)

165 (22)

351 (21)

Workers

327 (36)

257 (34)

584 (35)

Others (students, unemployed etc.)

38 (4)

25 (3)

63 (4)

(n = 973)

(n = 772)

(n = 1745)

Self-related depressive mood Not at all

520 (53)

618 (80)

1138 (65)

Sometimes sad

410 (42)

140 (18)

550 (32)

Depressive mood

43 (4)

14 (2)

57 (3)

(n = 951)

(n = 756)

(n = 1707)

Internalizing problems

r2 test

p = 0.535

p < 0.001

p < 0.001

(Youth Self Report) Normal range

790 (83)

675 (89)

1465 (86)

Problem range

161 (17)

81 (11)

242 (14)

(n = 951)

(n = 756)

(n = 1707)

Normal range

715 (75)

654 (87)

1369 (80)

Problem range

236 (25)

102 (14)

338 (20)

Externalizing problems (Youth Self Report)

62

p < 0.001

)LJ6WXG\SRSXODWLRQVJLUOVQ  ER\VQ  ERG\PDVVLQGH[%0, DW\HDUV 7KHPHDVXUHVDUHFDSWXUHGIURPWKHIRUPHU1)%&\HDUVWXG\$WWKLVDJHRI JLUOVDQGRIER\VZHUHREHVHRYHUZHLJKWDFFRUGLQJWR&ROH¶VFULWHULD

)LJ6WXG\SRSXODWLRQVJLUOVQ ER\VQ  ERG\PDVVLQGH[%0, DW\HDUV $WWKLVDJHRIJLUOVDQGRIER\VZHUHREHVHRYHUZHLJKWDFFRUGLQJWR&ROH¶V criteria.

63

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)LJ6WXG\SRSXODWLRQ¶VERG\PDVVLQGH[%0, DW\HDUV$WWKLVDJHRIJLUOV DQGRIER\VZHUHREHVHRYHUZHLJKWDFFRUGLQJWR&ROH¶VFULWHULD

64

)LJ6WXG\SRSXODWLRQ¶VJLUOVQ ER\VQ  ZDLVWFLUFXPIHUHQFHDW\HDUV

)LJ6WXG\SRSXODWLRQ¶VJLUOVQ ER\VQ  ZDLVWFLUFXPIHUHQFHDW\HDUV

65

GIRLS

BOYS

The area under the BMI vs. time curve

The area under the BMI vs. time curve

)LJ'LVWULEXWLRQRIWKHDUHDXQGHUWKHERG\PDVVLQGH[YVWLPHFXUYHRIJLUOVDQG boys between 7 and 18 years.

5.2

Prevalence of low back pain in the OBS cohort

$W  \HDUV JLUOV UHSRUWHG /%3 FDXVLQJ QR FRQVXOWDWLRQ IRU LW  PRUH RIWHQ WKDQ ER\V  vs.   7DEOH   ZKLOH  RI JLUOV DQG  RI ER\V UHSRUWHG /%3 UHTXLULQJPHGLFDOFRQVXOWDWLRQDW\HDUV7DEOH 7KHSUHYDOHQFHRI/%3ZDV DOVRKLJKHUDPRQJJLUOVWKDQER\VDW\HDUV7DEOH $WWKH\HDUIROORZXS VWXG\, WKHSUHYDOHQFHRI/%3ZDVDPRQJJLUOVDQGDPRQJER\V p   2IDGROHVFHQWVZLWKRXW/%3DW\HDUVRIJLUOVDQGRIER\VUHSRUWHG /%3DW\HDUVDQGRIJLUOVDQGRIER\VDW\HDUV7DEOH ³3HUVLVWHQW´ /%3ZDVPRUHFRPPRQDPRQJJLUOVWKDQER\V2IWKHDGROHVFHQWVZLWK/%3DW \HDUVRIJLUOVDQGRIER\VUHSRUWHG/%3DW\HDUVDQGRIJLUOVDQG RIER\VDW\HDUV

66

7DEOH3RLQWSUHYDOHQFH RI/%3GXULQJWKHSDVWPRQWKV LQWKH2%6SRSXODWLRQ DWWKHDJHVRIDQG\HDUV LBP symptoms

Girls

Boys

Total

% (n = 1079)

% (n = 908)

% (n = 1987)

(n = 973)

(n = 778)

(n = 1751)

No LBP

52 (510)

64 (500)

58 (1010)

Reporting LBP¹

43 (416)

31 (244)

38 (660)

Consultation for LBP²

5 (47)

4 (34)

5 (81)

(n = 1058)

(n = 882)

(n = 1940)

No LBP

38 (397)

53 (466)

45 (863)

Reporting LBP¹

57 (598)

42 (369)

50 (967)

Consultation for LBP²

6 (63)

5 (47)

6 (110)

LBP at 16 years

r2 test

p < 0.001

LBP at 18 years

p < 0.001

¹ Reporting LBP indicates adolescents who reported having had LBP during the past 6 months, but had not consulted a health professional because of their LBP. ² Consultation for LBP indicates adolescents who reported having had LBP during the past 6 months, and had consulted a health professional because of their LBP.

7DEOH  3UHYDOHQFH   RI /%3 DW  DQG  \HDUV LQ WKH 2%6 SRSXODWLRQ DPRQJ DGROHVFHQWVIUHHIURP/%3DW\HDUV LBP symptoms

LBP at 18 years

Girls

Boys

Total

% (n)

% (n)

% (n)

(n = 498)

(n = 488)

(n = 986)

No LBP

50 (247)

65 (319)

57 (566)

LBP¹

50 (251)

35 (169)

43 (420)

(n = 240)

(n = 210)

(n = 450)

No LBP

49 (118)

55 (115)

52 (233)

LBP¹

51 (122)

45 (95)

48 (217)

LBP at 19 years

r2 test

p < 0.001

p = 0.236

¹ LBP indicates any LBP (Reporting LBP and Consultation for LBP combined).

67

5.3

Associations between possible confounders and low back pain

When the raw data were analysed longitudinally combining both genders, the SUHYDOHQFHRI/%3DW\HDUVZDVKLJKHUDPRQJDGROHVFHQWVUHSRUWLQJ/%3DW \HDUVVPRNLQJDW\HDUVDQGDPRQJWKRVHZKRZHUHSK\VLFDOO\YHU\DFWLYHDW \HDUVp  GDWDQRWVKRZQ 7KHOHQJWKRIZRUNLQJKLVWRU\ZDVUHODWHG WR /%3 DW  \HDUV p    2I VSHFL¿F SK\VLFDO ZRUNORDG IDFWRUV NQHHOLQJ DQGDZNZDUGWUXQNSRVWXUHVZHUHUHODWHGWR/%3DW\HDUVp  %0,DW \HDUVDQGIDPLO\¶VVRFLRHFRQRPLFVWDWXVZHUHQRWVLJQL¿FDQWO\DVVRFLDWHGZLWK LBP. 5.4

Associations between possible risk factors and low back pain

5.4.1 Weight related factors (study I) Body mass index and LBP 7KH$8&PHWKRGZDVXVHGWRUHÀHFWWKHSRWHQWLDOORQJWHUPHIIHFWRIZHLJKWRQ WKH VSLQH$PRQJ ER\V WKH DUHD XQGHU WKH %0, EHWZHHQ  DQG  \HDUV FXUYH ZDV DVVRFLDWHG ZLWK ³LQFLGHQW´ /%3 DW  \HDUV DIWHU DGMXVWPHQW IRU VPRNLQJ and physical activity RR 1.15; 95% CI 1.00–1.31), while no such association was REVHUYHGHLWKHUIRU³SHUVLVWHQW´/%3DPRQJER\VRUIRU³LQFLGHQW´RU³SHUVLVWHQW´ LBP among girls (Table 10). In other words, a 1-unit rise in BMI during childhood WR\HDUV LQFUHDVHGWKHULVNRI/%3DW\HDUVDPRQJER\VIUHHIURP/%3DW \HDUVE\ $PRQJ JLUOV WKH $8& RI %0, IURP  WR  \HDUV ZDV DVVRFLDWHG ZLWK ³LQFLGHQW´/%3DW\HDUVDIWHUDGMXVWPHQWIRUVPRNLQJDQGSK\VLFDODFWLYLW\55 &,±7DEOH EXWQRWZLWK³SHUVLVWHQW´/%37KH¿QGLQJDW \HDUVPHDQVWKDWDXQLWULVHLQ%0,GXULQJWKDWWLPHVSDQLQFUHDVHGWKHULVNRI /%3DPRQJJLUOVIUHHIURP/%3DW\HDUVE\$PRQJER\VQRVWDWLVWLFDOO\ VLJQL¿FDQW DVVRFLDWLRQV EHWZHHQ %0, IURP  WR  \HDUV DQG /%3 ³LQFLGHQW´ RU ³SHUVLVWHQW´  ZHUH REVHUYHG 7DEOH   )XUWKHU DGMXVWPHQW IRU IDPLO\¶V VRFLRHFRQRPLFVWDWXVGLGQRWPDUNHGO\FKDQJHWKH55HVWLPDWHVIRU%0,GDWDQRW shown).

68

Waist circumference and LBP $PRQJER\VIUHHRI/%3D\HDUVDVHQWLPHWUHULVHLQ:&GXULQJWKH\HDU WLPH VSDQ LQFUHDVHG WKH ULVN RI /%3 DW  \HDUV E\  DIWHU DGMXVWPHQW IRU VPRNLQJDQGSK\VLFDODFWLYLW\55&,±7DEOH $PRQJJLUOV WKHUHZHUHQRVWDWLVWLFDOO\VLJQL¿FDQWDVVRFLDWLRQVEHWZHHQ:&DQG/%3)XUWKHU DGMXVWPHQWIRUIDPLO\¶VVRFLRHFRQRPLFVWDWXVGLGQRWPDUNHGO\FKDQJHWKHUHVXOWV (data not shown).

7DEOH5HODWLYHULVN55 RI³LQFLGHQW´ïDQG³SHUVLVWHQW´ð/%3ZLWKERG\PDVVLQGH[ %0, DVVHVVHGXVLQJWKHDUHDXQGHUWKHFXUYH$8& PHWKRGIURPWR\HDUVDQG IURPWR\HDUV/%3YVQR/%3  LBP at 18 yrs.

cases/n

Crude RR

95% CI

Adj. RR³

95% CI

“Incident” LBP

195/397

1.04

0.95–1.13

1.05

0.96–1.14

“Persistent” LBP

282/372

1.03

0.97–1.10

1.04

0.97–1.11

Girls AUC of BMI (7–16 yrs.)

AUC of BMI (16–18 yrs.) ”Incident” LBP

242/482

1.08

1.00–1.16

1.09

1.01–1.17

”Persistent” LBP

338/446

1.01

0.95–1.06

1.01

0.96–1.07

”Incident” LBP

125/392

1.14

0.99–1.30

1.15

1.00–1.31

”Persistent” LBP

145/210

1.02

0.98–1.07

1.02

0.97–1.07

Boys AUC of BMI (7–16 yrs.)

AUC of BMI (16–18 yrs.) ”Incident” LBP

162/472

1.06

0.94–1.19

1.04

0.93–1.17

”Persistent” LBP

184/260

1.03

0.95–1.11

1.03

0.95–1.12

¹ “Incident” LBP cases reported during the preceding 6-month period at 18 years of age but not at 16 years. ² “Persistent” LBP cases reported during the preceding 6-month period at both 16 and 18 years of age. ³ Adjusted for smoking and physical activity at 16 years of age.

69

7DEOH5HODWLYHULVN55 RI³LQFLGHQW´ïDQG³SHUVLVWHQW´ð/%3ZLWKZDLVWFLUFXPIHUHQFH :& DVVHVVHGXVLQJWKHDUHDXQGHUWKHFXUYH$8& PHWKRGIURPWR\HDUV/%3 vs. no LBP). LBP at 19 yrs.

cases/n

Crude RR

95% CI

Adj. RR³

95% CI

Girls AUC of WC (16–19 yrs.) “Incident” LBP

111/222

1.03

0.90–1.16

1.03

0.91–1.17

“Persistent” LBP

144/199

0.97

0.89–1.05

0.97

0.89–1.06

Boys AUC of WC (16–19 yrs.) ”Incident” LBP

89/195

1.15

1.02–1.31

1.16

1.02–1.32

”Persistent” LBP

72/132

0.94

0.78–1.13

0.92

0.75–1.13

¹ “Incident” LBP cases reported during the preceding 6-month period at 19 years of age but not at 16 years. ² “Persistent” LBP cases reported during the preceding 6-month period at both 16 and 19 years of age. ³ Adjusted for smoking and physical activity at 16 years of age.

5.4.2 Smoking (study II) 7KHSUHYDOHQFHRIVPRNLQJDFFRUGLQJWR/%3LVSUHVHQWHGLQ7DEOH$PRQJJLUOV IUHHRI/%3DW\HDUVVPRNLQJRYHUFLJDUHWWHVSHUGD\DW\HDUVRIDJHDQG PRUHWKDQSDFN\HDUVRIFXPXODWLYHVPRNLQJH[SRVXUHE\WKHDJHRI\HDUV ZHUHDVVRFLDWHGZLWK/%3DGM25&,±DQGDGM25&, ±UHVSHFWLYHO\ 7DEOH 5HJXODUVPRNLQJDW\HDUVZDVQRWVWDWLVWLFDOO\ VLJQL¿FDQWO\DVVRFLDWHGZLWK³LQFLGHQW´/%3DIWHUDGMXVWPHQWIRUFRYDULDWHV7DEOH 13). $PRQJ JLUOV ZLWK /%3 DW ERWK WLPH SRLQWV UHJXODU VPRNLQJ ZDV DVVRFLDWHG ZLWK/%3DGM25&,± 7DEOH 6RPHVWDWLVWLFDOO\VLJQL¿FDQW but no monotonic, associations were detected between the number of cigarettes VPRNHGSHUGD\DW\HDUVDQG³SHUVLVWHQW´/%37DEOH $PRQJERWKJHQGHUV WKHFXPXODWLYHDPRXQWRIVPRNLQJZDVVLJQL¿FDQWO\DVVRFLDWHGZLWK³SHUVLVWHQW´ /%3DGM25V± 7DEOH  $V WKHUH ZHUH RQO\ IHZ FDVHV ZKR KDG FRQVXOWHG D SURIHVVLRQDO IRU WKHLU symptoms, the genders were combined together to see whether the associations ZLWKVPRNLQJZHUHVLPLODULQWKHJURXSRIFDUHVHHNHUVFRPSDUHGWRRWKHUV$PRQJ DGROHVFHQWV ZLWK /%3 DOUHDG\ DW  \HDUV VHHNLQJ FDUH IRU /%3 ZDV DVVRFLDWHG ZLWKKHDY\VPRNLQJRYHUFLJDUHWWHVSHUGD\DW\HDUVDQGFXPXODWLYHDPRXQW 70

RIVPRNLQJPRUHWKDQSDFN\HDUVDW\HDUV DGM25V± 7DEOH ,Q DGGLWLRQDOOWKHVPRNLQJSDUDPHWHUVZHUHDVVRFLDWHGZLWK³SHUVLVWHQW´/%3FDXVLQJ QRFDUHVHHNLQJDGM25V± 7DEOH $PRQJDGROHVFHQWVIUHHIURP/%3 DW\HDUVZHDNHUDVVRFLDWLRQVZHUHREVHUYHGEHWZHHQVPRNLQJSDUDPHWHUVDQG ¶5HSRUWLQJ/%3¶ZKLOHVPRNLQJSDUDPHWHUVZHUHQRWVLJQL¿FDQWO\DVVRFLDWHGZLWK ’Consultation for LBP’ (Table 15). $PRQJ JLUOV DQ H[SRVXUHUHVSRQVH UHODWLRQVKLS ZDV REVHUYHG EHWZHHQ WKH FXPXODWLYHDPRXQWRIVPRNLQJSDFN\HDUV DQGERWK³LQFLGHQW´DQG³SHUVLVWHQW´ /%3E\WKHȤWHVWIRUWUHQGZKHUHDVDPRQJER\VWKHDVVRFLDWLRQZDVLQFRQVLVWHQW 6LPLODUO\DQH[SRVXUHUHVSRQVHUHODWLRQVKLSRIFXPXODWLYHDPRXQWRIVPRNLQJZDV REVHUYHGDPRQJDGROHVFHQWVUHSRUWLQJ³SHUVLVWHQW´/%3ZLWKFDUHVHHNLQJ The adjustment for gender, BMI, physical activity, depressive mood, and family’s socioeconomic status was used in the analyses. It is noteworthy that almost DOODGMXVWHGRGGVUDWLRVIRUVPRNLQJZHUHKLJKHUWKDQWKHFUXGHRQHV

7DEOH7KHSUHYDOHQFH RIVPRNLQJLQWKHVWXG\SRSXODWLRQDPRQJ³LQFLGHQW´ïDQG ³SHUVLVWHQW´ð/%3FDVHV Girls

Boys

”Incident”

”Persistent”

”Incident”

”Persistent”

% (n)

% (n)

% (n)

% (n)

Non-smokers

64 (158)

58 (202)

69 (114)

64 (119)

Non-regular smokers

19 (47)

23 (81)

18 (29)

20 (38)

Regular smokers³

17 (41)

18 (64)

13 (22)

16 (29)

Non-smokers

56 (140)

48 (168)

57 (95)

46 (85)

Non-regular smokers

20 (49)

22 (77)

13 (21)

23 (42)

Regular smokers³

25 (62)

29 (102)

30 (50)

32 (60)

Smoking Smoking at 16 yrs.

Smoking at 18 yrs.

¹ “Incident” LBP cases reported during the preceding 6-month period at 18 years of age but not at 16 years. ² “Persistent” LBP cases reported during the preceding 6-month period at both 16 and 18 years of age. ³ 5–7 d/week.

71

72 35/56

> 1.5

1.78

1.67

1.00

2.08

1.43

1.00

1.86

1.00

Crude OR

Girls

0.99–3.18

0.97–2.87

0.94–4.59

0.83–2.48

1.08–3.19

95% CI

2.20

1.49

2.80

1.32

1.83

Adj. OR

1.13–4.28

0.82–2.71

1.11–7.09

0.73–2.41

0.98–3.43

95% CI

28/73

26/51

96/301

13/34

18/42

128/390

22/59

114/351

cases/n

² 5–7 d/week.

¹ “Incident” LBP cases reported during the preceding 6-month period at 18 years of age but not at 16 years.

39/64

0.1–1.5

0

163/337

19/29

>9

Pack-years at 18 yrs.

34/60

188/394

41/66

158/337

cases/n

1–9

0

Cigarettes/d at 16 yrs.

Regular smokers²

Non-smokers

Smoking at 16 yrs.

Smoking

1.33

2.22

1.00

1.27

1.54

1.00

1.24

1.00

Crude OR

0.78–2.26

1.22–4.05

0.62–2.61

0.80–2.93

0.70–2.19

95% CI

Boys

1.52

2.09

1.71

1.72

1.38

Adj. OR

0.82–2.82

1.08–4.06

0.72–4.01

0.85–3.50

0.71–2.67

95% CI

Table 13. Association of smoking with “incident”¹ LBP. Crude odds ratios (OR) and ORs adjusted for family’s socioeconomic status, physical activity, body mass index, and depressive mood at 16 years.

73

60/81

1.79 2.37

Girls

1.39–4.05

1.07–3.00

0.85–3.95

1.38–3.64

1.38–3.78

95% CI

2.89

1.77

2.57

2.39

2.52

Adj. OR

1.54–5.45

1.01–3.11

1.03–6.46

1.40–4.08

1.40–4.53

95% CI

41/86

30/55

96/301

19/40

25/49

134/396

29/66

119/356

cases/n

² 5–7 d/week.

¹ “Persistent” LBP cases reported during the preceding 6-month period at both 16 and 18 years of age.

54/79

> 1.5

1.00

1.83

22/32

210/384

2.24

70/96

1.00

2.28

64/89

248/454

1.00

Crude OR

201/380

cases/n

0.1–1.5

0

Pack-years at 18 yrs.

>9

1–9

0

Cigarettes/d at 16 yrs.

Regular smokers²

Non-smokers

Smoking at 16 yrs.

Smoking

1.95

2.56

1.00

1.77

2.04

1.00

1.56

1.00

Crude OR

1.20–3.17

1.43–4.59

0.92–3.40

1.12–3.70

0.92–2.66

95% CI

Boys

2.52

2.92

2.18

2.68

1.86

Adj. OR

1.39–4.57

1.48–5.77

0.95–4.98

1.35–5.32

0.98–3.53

95% CI

Table. 14. Association of smoking with “persistent”¹ LBP. Crude odds ratios (OR) and ORs adjusted for family’s socioeconomic status, physical activity, body mass index, and depressive mood at 16 years.

74 1.74

1–1.5

> 1.5

1.10–2.73

2.15

1.14

1.00

3.56

1.49

1.00

2.12

1.00

Adj. OR

0.79–5.84

0.36–3.65

0.91–13.97

0.52–4.28

0.82–5.45

95% CI

2.69

2.25

1.00

2.37

2.42

1.00

2.12

1.00

Adj. OR

³ 5–7 d/week.

² “Persistent” LBP cases reported during the preceding 6-month period at both 16 and 18 years of age.

2.06 5.82

1.74–4.15

1.00

7.01

0.85

1.00

3.27

1.00

Adj. OR

1.44–3.53

1.25–4.50

1.57–3.75

1.37–3.30

95% CI

1.39–24.42

0.36–11.70

1.60–30.84

0.10–7.23

0.92–11.67

95% CI

Consultation for LBP

”Persistent”² LBP Reporting LBP

¹ “Incident” LBP cases reported during the preceding 6-month period at 18 years of age but not at 16 years.

1.00 1.82

0 1.16–2.86

1.09–3.81

2.04

Pack-years at 18 yrs.

>9

0.91–2.33

1.00 1.46

1–9

0.97–2.42

95% CI

Consultation for LBP

”Incident”¹ LBP

0

Cigarettes/d at 16 yrs.

1.00 1.53

Regular smokers³

Adj. OR

Non-smokers

Smoking at 16 yrs.

Smoking

Reporting LBP

7DEOH  $VVRFLDWLRQ RI VPRNLQJ ZLWK ³LQFLGHQW´ DQG ³SHUVLVWHQW´ /%3 E\ VHHNLQJ FDUH IRU /%3 V\PSWRP 2GGV UDWLRV 25V  DGMXVWHGIRUJHQGHUIDPLO\¶VVRFLRHFRQRPLFVWDWXVSK\VLFDODFWLYLW\ERG\PDVVLQGH[DQGGHSUHVVLYHPRRGDW\HDUV5HSRUWLQJ LBP indicates that adolescents reported LBP but had not consulted a health professional for it.

5.4.3 Physical workload (study III) Working history and physical workload factors 2IWKHDGROHVFHQWVZLWKRXW/%3DW\HDUEDVHOLQHJLUOV DQGER\V   KDG EHHQ ZRUNLQJ GXULQJ WKH \HDU IROORZXS 7KH ZRUN H[SRVXUH ZDV DVVHVVHGUHWURVSHFWLYHO\DW\HDUV7KHPHDQ6' GXUDWLRQRIZRUNZDV  PRQWKV*LUOVKDGEHHQZRUNLQJVOLJKWO\ORQJHUWKDQER\V PRQWKVvs.  PRQWKV 7ZHQW\SHUFHQWRIWKHGDXJKWHUVRIWKHVHOIHPSOR\HGIDWKHUV PRWKHUVZHUHZRUNLQJDW\HDUVRIDJHvs.RIDOOWKHJLUOV GDWDQRWVKRZQ  ,QIUHTXHQWO\UHSRUWHGVSHFL¿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•KGD\$PRQJER\VWKHH[SRVXUHVPRUHIUHTXHQWO\VHHQ LQFRPELQDWLRQVWKDQDORQHZHUHNQHHOLQJRUVTXDWWLQJGULYLQJPDQXDOKDQGOLQJ RI PHGLXP ZHLJKW RU KHDY\ REMHFWV ZRUNLQJ ZLWK KDQGV DERYH VKRXOGHU OHYHO DZNZDUGWUXQNSRVWXUHVDQGVWDQGLQJRUZDONLQJ•KGD\ 7KHRSWLPDOQXPEHURI/&$FOXVWHUVZDVGHWHUPLQHGDVWKUHHIRUJLUOVDQGIRXU for boys. Latent class clusters of girls $PRQJJLUOV&OXVWHUµ5HIHUHQFH¶ FRQVLVWHGRIVXEMHFWVZKRZHUHQRWH[SRVHGWR DQ\VSHFL¿FZRUNORDG*LUOVLQ&OXVWHUµ$ZNZDUGWUXQNSRVWXUHV¶ ZHUHH[SRVHG WRNQHHOLQJZRUNLQJZLWKKDQGVDERYHWKHVKRXOGHUOHYHODZNZDUGWUXQNSRVWXUHV DQG VWDQGLQJ RU ZDONLQJ *LUOV LQ &OXVWHU  µ3K\VLFDOO\ GHPDQGLQJ MRE¶  ZHUH H[SRVHGWRNQHHOLQJPDQXDOKDQGOLQJPHGLXPRUKHDY\REMHFWV ZRUNLQJZLWK KDQGVDERYHVKRXOGHUVDZNZDUGWUXQNSRVWXUHDQGVWDQGLQJRUZDONLQJ7DEOH 

75

Latent class clusters of boys $PRQJER\V&OXVWHUµ5HIHUHQFH¶ FRQVLVWHGRIVXEMHFWVZKRZHUHQRWH[SRVHG WR DQ\ VSHFL¿F ZRUNORDG %R\V LQ &OXVWHU  µ$ZNZDUG WUXQN SRVWXUHV¶  ZHUH H[SRVHGWRNQHHOLQJZRUNLQJZLWKKDQGVDERYHVKRXOGHUVDZNZDUGWUXQNSRVWXUHV DQG VWDQGLQJ RU ZDONLQJ %R\V LQ &OXVWHU  µ0DQXDO KDQGOLQJ¶  ZHUH H[SRVHG WR PDQXDO KDQGOLQJ PHGLXP RU KHDY\ REMHFWV  DQG VWDQGLQJ RU ZDONLQJ ZKLOH ER\VLQ&OXVWHUµ3K\VLFDOO\GHPDQGLQJMRE¶ ZHUHH[SRVHGWRDOOVHYHQVSHFL¿F ZRUNORDGV7DEOH 

76

77

29 (16) 31 (68) 29 (94) 36 (176)

Manual handling of medium weight objects

Manual handling of heavy objects

Working hands above shoulders

Awkward trunk postures

Standing or walking

58 (283)

64 (203)

63 (135)

69 (38)

63 (89)

20 (1)

62 (215)

% (n)

Reporting LBP

Girls (n = 1079)

6 (30)

7 (22)

6 (12)

2 (1)

4 (6)

20 (1)

3 (12)

% (n)

for LBP

Consultation

49 (187)

41 (95)

41 (79)

44 (84)

46 (114)

44 (35)

40 (97)

% (n)

No LBP

44 (170)

53 (121)

51 (97)

50 (94)

48 (120)

49 (39)

54 (129)

% (n)

Reporting LBP

Boys (n = 905)

7 (25)

6 (13)

8 (16)

6 (12)

6 (14)

7 (6)

6 (15)

% (n)

for LBP

Consultation

ZDONLQJIRU•KGD\

WUXQNSRVWXUHVGH¿QHGDVZRUNVWDQGLQJRURQNQHHVLQDSRVLWLRQOHDQLQJIRUZDUGZLWKRXWVXSSRUWIRU•KGD\6WDQGLQJRUZDONLQJGH¿QHGDVVWDQGLQJRU

NJ•WLPHVGD\:RUNLQJZLWKKDQGVDERYHVKRXOGHUVGH¿QHGDVZRUNLQYROYLQJKROGLQJXSSHUOLPEV DERYHVKRXOGHUOHYHOIRU•KGD\$ZNZDUG

•NJDWOHDVWWLPHVPLQXWHIRU•KGD\0DQXDOKDQGOLQJRIKHDY\REMHFWVGH¿QHGDVZRUNLQYROYLQJPDQXDOO\OLIWLQJFDUU\LQJRUSXVKLQJREMHFWV•

YHKLFOH •KGD\RYHUPRQWKV\HDU0DQXDOKDQGOLQJRIPHGLXPZHLJKWREMHFWVGH¿QHGDVZRUNLQYROYLQJPDQXDOO\OLIWLQJFDUU\LQJRUSXVKLQJREMHFWV

ï.QHHOLQJGH¿QHGDVZRUNLQYROYLQJNQHHOLQJRUVTXDWWLQJIRU•KGD\'ULYLQJGH¿QHGDVZRUNLQYROYLQJGULYLQJDPRWRUYHKLFOHFDUWUXFNRURWKHUZRUNLQJ

60 (3) 33 (46)

Driving

35 (122)

% (n)

Kneeling

Physical workload¹

No LBP

7DEOH3UHYDOHQFH RI/%3DW\HDUVRIDJHLQUHODWLRQWRSK\VLFDOZRUNH[SRVXUHV5HSRUWLQJ/%3LQGLFDWHVWKDWDGROHVFHQWV reported LBP but had not consulted a health professional for it.

78 6 (1) 5 (1) 12 (2) 32 (5)

Manual handling of medium weight objects

Manual handling of heavy objects

Working hands above shoulders

Awkward trunk postures 238 (75)

214 (67)

145 (46)

0 (0)

16 (5)

236 (74)

n (%)

Cluster 3

132 (99)

73 (55)

58 (43)

50 (37)

119 (89)

80 (60)

n (%)

(n = 134)

All

489 (46)

319 (30)

215 (20)

55 (5)

141 (13)

349 (33)

n (%)

(n= 1058)

p < 0.001

p < 0.001

p < 0.001

p < 0.001

p < 0.001

p < 0.001

r2 test

Cluster 1 = Reference, Cluster 2 = Awkward trunk postures, Cluster 3 = Physically demanding job

The percentage of exposed participants is representative of the relative proportion of those who gave a positive answer to the question concerned.

119 (20)

33 (5)

Kneeling

Standing or walking

n (%)

Cluster 2 (n = 318)

Cluster 1 (n = 606)

Physical workload

Girls

7DEOH'LVWULEXWLRQRISK\VLFDOZRUNORDGIDFWRUVLQHDFKODWHQWFODVVDQDO\VLV/&$ FOXVWHULQJLUOV

79

0 (0) 6 (1) 0 (0)

Manual handling of medium weight objects

Manual handling of heavy objects

Working hands above shoulders

Awkward trunk postures 89 (59)

99 (65)

62 (41)

0 (0)

0 (0)

15 (10)

107 (70)

n (%)

Cluster 3

78 (66)

22 (19)

1(1)

64 (54)

93 (79)

19 (16)

0 (0)

n (%)

(n = 118)

Cluster 4

146 (80)

108 (59)

123 (68)

126 (69)

155 (85)

28 (15)

134 (74)

n (%)

(n = 182)

All

382 (43)

229 (26)

192 (22)

190 (22)

248 (28)

80 (9)

241 (27)

n (%)

(n= 880)

p < 0.001

p < 0.001

p < 0.001

p < 0.001

p < 0.001

p < 0.001

p < 0.001

r2 test

Cluster 1 = Reference, Cluster 2 = Awkward trunk postures, Cluster 3 = Manual handling, Cluster 4 = Physically demanding job

The percentage of exposed participants is representative of the relative proportion of those who gave a positive answer to the question concerned.

69 (16)

0 (0)

Driving

Standing or walking

0 (0) 18 (4)

Kneeling

n (%)

Cluster 2 (n = 152)

Cluster 1 (n = 428)

Physical workload

Boys

7DEOH'LVWULEXWLRQRISK\VLFDOZRUNORDGIDFWRUVLQHDFKODWHQWFODVVDQDO\VLV/&$ FOXVWHULQER\V

Association of physical workload factors and low back pain ,Q JLUOV IUHH IURP /%3 DW  \HDUV ZRUNLQJ UHJXODUO\ RU LUUHJXODUO\ LQFUHDVHG VLJQL¿FDQWO\WKHULVNRI/%3DW\HDUVDGM55&,± 7DEOH  ,QDGGLWLRQWKHGXUDWLRQRIZRUNH[SRVXUHZDVDVVRFLDWHGZLWK³LQFLGHQW´/%3VR WKDW55SHULQFUHPHQWRIRQHPRQWKRIZRUNH[SRVXUHUDQJHGIURPER\V WR JLUOV 7DEOH 2IVSHFL¿FSK\VLFDOZRUNORDGIDFWRUVWKHULVNRI³LQFLGHQW´ LBP was increased in girls exposed to manual handling of medium weight objects DGM55&,± DQGDZNZDUGWUXQNSRVWXUHVDGM55&, ±  ,Q ER\V WKH ULVN RI ³LQFLGHQW´ /%3 ZDV LQFUHDVHG LQ WKRVH H[SRVHG WR NQHHOLQJDGM55&,± ZRUNLQJZLWKKDQGVDERYHVKRXOGHUOHYHO DGM55&,± DQGDZNZDUGWUXQNSRVWXUHVDGM55&, 1.3–2.2; Table 20). ,Q DGROHVFHQWV ERWK JHQGHUV  IUHH IURP /%3 DW  \HDUV ¶$ZNZDUG WUXQN postures’ and ’Physically demanding job’ clusters were associated with LBP at  \HDUV7KH 55V RI WKHVH FOXVWHUV UDQJHG IURP  WR  DIWHU DGMXVWPHQW IRU VPRNLQJDQGOHLVXUHWLPHSK\VLFDODFWLYLW\7DEOH  ,Q DGROHVFHQWV HLWKHU JLUOV RU ER\V  ZLWK /%3 DW  \HDUV /%3 DW  \HDUV ZDVQRWDVVRFLDWHGZLWKZRUNLQJUHJXODUO\RULUUHJXODUO\GXUDWLRQRIZRUNVSHFL¿F SK\VLFDOZRUNORDGIDFWRUVRU/&$FOXVWHUVGDWDQRWVKRZQ 

7DEOH  5LVN RI ³LQFLGHQW´ /%3 DFFRUGLQJ WR WKH PDLQ DFWLYLW\ DQG GXUDWLRQ RI ZRUN H[SRVXUHGXULQJIROORZXSQ   Girls (n = 498)

Boys (n = 488)

Adj. RR¹ (95% CI)

Adj. RR¹ (95% CI)

1.0

1.0

Working regularly or irregularly

1.48 (1.23–1.79)

0.88 (0.62–1.24)

Other/data missing

1.23 (0.96–1.57)

0.82 (0.55–1.24)

1.15 (1.03–1.29)

1.12 (0.97–1.29)

Work exposure Main activity Studying

Duration of work exposure²

¹ Adjusted for smoking and leisure time physical activity at 16 years of age. ² RR per increment of one month.

80

7DEOH  5LVNUDWLRV 55V  RI/%3DW \HDUV DPRQJ DGROHVFHQWV ZLWKRXW /%3DW  \HDUVDFFRUGLQJWRVSHFL¿FSK\VLFDOZRUNORDGIDFWRUVQ   Girls (n = 498)

Boys (n = 488)

Adj. RR² (95% CI)

Adj. RR² (95% CI)

Kneeling

1.12 (0.93–1.35)

1.74 (1.37–2.20)

Driving

0.64 (0.13–3.20)

1.36 (0.93–1.98)

Manual handling of medium weight objects

1.30 (1.04–1.62)

1.11 (0.86–1.45)

Manual handling of heavy objects

1.17 (0.81–1.69)

1.15 (0.86–1.55)

Working hands above shoulders

1.20 (0.97–1.48)

1.32 (1.00–1.75)

Awkward trunk postures

1.23 (1.03–1.48)

1.69 (1.33–2.15)

Standing or walking

1.07 (0.90–1.28)

1.23 (0.96–1.57)

Physical workload¹

ï.QHHOLQJGH¿QHGDVZRUNLQYROYLQJNQHHOLQJRUVTXDWWLQJIRU•KGD\'ULYLQJGH¿QHGDVZRUNLQYROYLQJ GULYLQJDPRWRUYHKLFOHFDUWUXFNRURWKHUZRUNLQJYHKLFOH •KGD\RYHUPRQWKV\HDU0DQXDO KDQGOLQJRIPHGLXPZHLJKWREMHFWVGH¿QHGDVZRUNLQYROYLQJPDQXDOO\OLIWLQJFDUU\LQJRUSXVKLQJ REMHFWV•NJDWOHDVWWLPHVPLQXWHIRU•KGD\0DQXDOKDQGOLQJRIKHDY\REMHFWVGH¿QHGDVZRUN LQYROYLQJPDQXDOO\OLIWLQJFDUU\LQJRUSXVKLQJREMHFWV•NJ•WLPHVGD\:RUNLQJZLWKKDQGVDERYH VKRXOGHUVGH¿QHGDVZRUNLQYROYLQJKROGLQJXSSHUOLPEV DERYHVKRXOGHUOHYHOIRU•KGD\$ZNZDUG WUXQNSRVWXUHVGH¿QHGDVZRUNVWDQGLQJRURQNQHHVLQDSRVLWLRQOHDQLQJIRUZDUGZLWKRXWVXSSRUWIRU• KGD\6WDQGLQJRUZDONLQJGH¿QHGDVVWDQGLQJRUZDONLQJIRU•KGD\ ²Adjusted for smoking and leisure time physical activity at 16 years of age.

81

82 55 (11)

Physically demanding job

1.35

1.28

1.00

RR¹

Girls

(1.05–1.74)

(1.05–1.55)

(95% CI)

74 (15)

88 (18)

82 (17)

244 (50)

n (%)

1.06

1.55

1.85

1.00

RR¹

Boys

Clustering was performed using latent class analysis (LCA) (n = 986). There are three clusters among girls and four among boys.

¹ Adjusted for smoking and leisure time physical activity at 16 years of age.

Manual handling (boys)

300 (60) 143 (29)

Awkward trunk postures

n (%)

Reference

LCA clusters

(0.70–1.61)

(1.14–2.12)

(1.38–2.48)

(95% CI)

Table 21. Risk ratios (RRs) of LBP at 18 years among adolescents without LBP at baseline according to clusters of physical workload factors.

5.4.4 Family’s socioeconomic status and low back pain $PRQJJLUOVWKHUHZDVDVLJQL¿FDQWDVVRFLDWLRQEHWZHHQKDYLQJDVHOIHPSOR\HG IDWKHURUVRPHWLPHVPRWKHU DQGSUHYDOHQFHRI/%3DW\HDUVFUXGH55  &, ±  7DEOH   7KH LQFOXVLRQ RI SRWHQWLDO FRQIRXQGHUV VPRNLQJ OHLVXUHWLPHSK\VLFDODFWLYLW\DQG%0, GLGQRWPDUNHGO\FKDQJHWKHUHVXOWVDGM 55   &, ±  $PRQJ ER\V QR VWDWLVWLFDOO\ VLJQL¿FDQW DVVRFLDWLRQV ZHUHIRXQGEHWZHHQIDPLO\¶VVRFLRHFRQRPLFVWDWXVDQGSUHYDOHQFHRI/%3DW years of age (Table 22). 7KHSRVVLEOHDVVRFLDWLRQEHWZHHQIDPLO\¶VVRFLRHFRQRPLFVWDWXVDQG³LQFLGHQW´ DQG ³SHUVLVWHQW´ /%3 ZDV DQDO\VHG DW WKH \HDU IROORZXS RI WKH 2%6 FRKRUW SRSXODWLRQ $PRQJ JLUOV WKHUH ZDV D VLJQL¿FDQW DVVRFLDWLRQ EHWZHHQ KDYLQJ D VHOIHPSOR\HGIDWKHURUVRPHWLPHVPRWKHU DQG³SHUVLVWHQW´/%3DW\HDUVRI DJHFUXGH55&,±DQGDGM55&,±7DEOH  $GGLWLRQDOO\WKHIDPLO\¶VVRFLRHFRQRPLFVWDWXVµVRPHWKLQJHOVH¶ZDVVLJQL¿FDQWO\ DVVRFLDWHGZLWK³SHUVLVWHQW´/%3DPRQJJLUOVFUXGH55&,±DQG DGM55&,± 7DEOH $PRQJER\VQRQHRIWKHVRFLRHFRQRPLF FODVVHVZHUHDVVRFLDWHGZLWK³SHUVLVWHQW´/%37DEOH 7KHUHZHUHQRVWDWLVWLFDOO\ VLJQL¿FDQWDVVRFLDWLRQVEHWZHHQWKHVHVRFLRHFRQRPLFFODVVHVDQG³LQFLGHQW´/%3 among girls or boys (data not shown).

83

Table 22. Relative risks (RR) of LBP (LBP; Reporting LBP and Consultation for LBP FRPELQHG  DW  \HDUV DFFRUGLQJ WR IDPLO\¶V VRFLRHFRQRPLF VWDWXV FURVVVHFWLRQDO VWXG\RIWKH1)%&FRKRUW  Family’s socioeconomic status

crude RR

95% CI

Adj. RR¹

95% CI

Girls (n = 3273) Higher clerical employees

1.04

0.94–1.14

1.06

0.97–1.17

Self-employed persons

1.11

1.00–1.23

1.13

1.02–1.26

Lower clerical employees

1.04

0.95–1.14

1.05

0.96–1.15

Workers

1.00

–

1.00

–

Others (students, unemployed, etc.)

1.05

0.87–1.26

1.06

0.89–1.28

0.93

0.82–1.05

0.92

0.82–1.05

Boys (n = 3108) Higher clerical employees Self-employed persons

1.03

0.89–1.19

1.06

0.91–1.22

Lower clerical employees

1.03

0.90–1.16

1.02

0.90–1.15

Workers

1.00

–

1.00

–

Others (students, unemployed, etc.)

0.96

0.72–1.28

0.99

0.75–1.31

¹ Adjustment for body mass index, smoking, and leisure time physical activity at 16 years of age.

7DEOH5HODWLYHULVNV55 RI³SHUVLVWHQW´/%3/%3DWERWKDQG\HDUV DW \HDUVZLWKIDPLO\¶VVRFLRHFRQRPLFVWDWXVIROORZXSVWXG\RIWKH2%6FRKRUW  Family’s socioeconomic status

crude RR

95% CI

Adj. RR¹

95% CI

0.98–1.42

Girls (n = 534) Higher clerical employees

1.16

0.96–1.40

1.18

Self-employed persons

1.30

1.03–1.63

1.38

1.11–1.73

Lower clerical employees

1.16

0.95–1.42

1.14

0.94–1.39

Workers

1.00

–

1.00

–

Others (students, unemployed, etc.)

1.38

1.02–1.87

1.41

1.05–1.90

Boys (n = 471) Higher clerical employees

0.85

0.63–1.41

0.96

0.86–1.06

Self-employed persons

1.28

0.90–1.81

1.07

0.91–1.26 0.88–1.12

Lower clerical employees

0.96

0.70–1.32

0.99

Workers

1.00

–

1.00

–

Others (students, unemployed, etc.)

1.06

0.53–2.13

1.03

0.75–1.43

¹ Adjustment for body mass index, smoking, and leisure time physical activity at 16 years of age.

84

5.4.5 Co-occurrence of psychosocial and lifestyle factors (study IV) The description of the study population 3V\FKRVRFLDO GHVFULSWLRQ RI WKH VWXG\ SRSXODWLRQ LV SUHVHQWHG LQ 7DEOH  $W  \HDUV  RI JLUOV DQG  RI ER\V EHORQJHG WR WKH SUREOHP UDQJH LQ WKH LQWHUQDOL]LQJVFDOHZKLOHRIJLUOVDQGRIER\VEHORQJHGWRWKHSUREOHP UDQJHLQWKHH[WHUQDOL]LQJVFDOH7DEOH  $V UHJDUGV OLIHVW\OH YDULDEOHV  RI JLUOV DQG  RI ER\V ZHUH SK\VLFDOO\ LQDFWLYHKRXU093$SHUZHHN /HLVXUHWLPHDPRXQWRIVLWWLQJZDVKLJKDPRQJ RIJLUOVDQGRIER\V•KRXUVSHUGD\ 7KHDYHUDJHVOHHSLQJWLPHZDVOHVV WKDQKRXUVSHUGD\DPRQJRIJLUOVDQGRIER\V7KUHHSHUFHQWRIJLUOVDQG RIER\VZHUHREHVH7ZHQW\SHUFHQWRIWKHJLUOVDQGRIWKHER\VZHUHVPRNHUV Psychosocial and lifestyle characteristics of the clusters 7KH/&$PRGHOIRUJLUOVGHWHUPLQHGDQRSWLPDOQXPEHURIFOXVWHUVWREHIRXU0RVW RI WKH JLUOV   ZHUH DOORFDWHG WR WKH UHIHUHQFH FOXVWHU FOXVWHU    WR WKH H[WHUQDOL]LQJEHKDYLRXUFOXVWHUFOXVWHU WRWKHPXOWLSOHULVNEHKDYLRXUFOXVWHU FOXVWHU DQGWRWKHREHVHFOXVWHUFOXVWHU 7KHUHIHUHQFHFOXVWHULQFOXGHG girls with a favourable distribution of both psychosocial and lifestyle factors. The H[WHUQDOL]LQJ EHKDYLRXU FOXVWHU FRQVLVWHG RI JLUOV ZLWK WKH KLJKHVW OLNHOLKRRG RI H[WHUQDOL]LQJV\PSWRPVDQGTXLWHDKLJKSUREDELOLW\RILQWHUQDOL]LQJSUREOHPVEXW they were the least inactive and they had the least sitting time as compared with JLUOVLQRWKHUFOXVWHUV7KHPXOWLSOHULVNEHKDYLRXUVFOXVWHULQFOXGHGJLUOVZLWKWKH KLJKHVWSUREDELOLW\RILQWHUQDOL]LQJSUREOHPVDQGRIJLUOVKDGDOVRH[WHUQDOL]LQJ problems. Moreover, the probability of adverse lifestyle factors, with the exception of obesity, was high among these girls. Girls in the obese cluster had the highest BMI PHDQ%0,&,± 7KHGLVWULEXWLRQRISV\FKRVRFLDODQGOLIHVW\OHIDFWRUV E\FOXVWHUFDWHJRU\DPRQJJLUOVLVSUHVHQWHGLQ)LJ $PRQJER\VWKHIRXUFOXVWHU/&$PRGHOZDVDOVRVXSHULRUWRWKHRWKHUPRGHOV WHVWHG$SSUR[LPDWHO\KDOIRIWKHER\V ZHUHDOORFDWHGWRWKHUHIHUHQFHFOXVWHU FOXVWHU    WR WKH VHGHQWDU\ FOXVWHU FOXVWHU    WR WKH H[WHUQDOL]LQJ EHKDYLRXUFOXVWHUFOXVWHU DQGWRWKHREHVHFOXVWHUFOXVWHU 7KHUHIHUHQFH cluster represented boys with a low probability of psychosocial symptoms and D KLJK OLNHOLKRRG RI IDYRXUDEOH OLIHVW\OH IDFWRUV7KH VHGHQWDU\ FOXVWHU FRQVLVWHG of boys with the greatest probability of physical inactivity, high sitting time, and 85

VKRUWHUVOHHSLQJWLPHV%R\VLQWKHH[WHUQDOL]LQJEHKDYLRXUFOXVWHUKDGWKHKLJKHVW SUREDELOLW\RISV\FKRVRFLDOV\PSWRPVDQGVPRNLQJEXWWKH\ZHUHSK\VLFDOO\TXLWH active. Boys in the obese cluster were physically inactive and had a high BMI PHDQ %0,  &, ±  7KH GLVWULEXWLRQ RI SV\FKRVRFLDO DQG OLIHVW\OH IDFWRUVE\FOXVWHUFDWHJRU\DPRQJER\VLVSUHVHQWHGLQ)LJ Prevalence of low back pain in relation to clusters The distribution of LBP at different ages according to psychosocial and lifestyle clusters LVSUHVHQWHGLQWDEOHV±7KHKLJKHVWSUHYDOHQFHRIµ5HSRUWLQJ/%3¶ZDVVHHQLQWKH H[WHUQDOL]LQJFOXVWHUVDPRQJERWKJLUOV DQGER\V ZKLOHRIJLUOVLQ WKHPXOWLSOHULVNEHKDYLRXUVFOXVWHUUHSRUWHGµ&RQVXOWDWLRQIRU/%3¶DW\HDUV7DEOH ± $W\HDUVRIJLUOVIUHHIURP/%3DW\HDUVUHSRUWHGµ&RQVXOWDWLRQ IRU/%3¶7DEOH ,QWKHREHVHFOXVWHUWKHSURSRUWLRQRIER\VUHSRUWLQJQHZ/%3DW \HDUVZDVORZZKLOHRIWKHER\VLQWKLVFOXVWHUUHSRUWHGµ1R/%3¶7DEOH  Association of psychosocial and lifestyle clusters with low back pain at 16 years (cross-sectional study) $PRQJJLUOVLQGLYLGXDOVLQWKHPXOWLSOHULVNEHKDYLRXUVFOXVWHUZHUHDOPRVWWKUHH WLPHV DQG WKRVH LQ H[WHUQDOL]LQJ EHKDYLRXU DQG REHVH FOXVWHU FORVH WR WZR WLPHV PRUHOLNHO\WRUHSRUWµ&RQVXOWDWLRQIRU/%3¶DW\HDUV55&,± 55&,±DQG55&,±UHVSHFWLYHO\ FRPSDUHGWR WKH UHIHUHQFH FOXVWHU 7DEOH   ,Q DGGLWLRQ JLUOV LQ WKH H[WHUQDOL]LQJ EHKDYLRXU DQGPXOWLSOHULVNEHKDYLRXUVFOXVWHUVZHUHDOPRVWRQHDQGDKDOIWLPHVPRUHOLNHO\ WR UHSRUW /%3 ZLWK QR FDUH VHHNLQJ 55   &, ± 55   &, ±  5HJDUGLQJ WKH UHVXOWV RI ER\V WKH H[WHUQDOL]LQJ EHKDYLRXU FOXVWHU ZDV VLJQL¿FDQWO\DVVRFLDWHGZLWKµ&RQVXOWDWLRQIRU/%3¶55&,± DQG µ5HSRUWLQJ/%3¶55&,± 7DEOH  Association of psychosocial and lifestyle clusters with new low back pain at two-year follow-up 7KH H[WHUQDOL]LQJ EHKDYLRXU FOXVWHU DVVRFLDWHG VLJQL¿FDQWO\ ZLWK ¶&RQVXOWDWLRQ IRU /%3¶DW\HDUVDPRQJJLUOVZLWKQR/%3DW\HDUV55&,± 7DEOH 31). None of the cluster of boys associated with new LBP in the follow-up (Table 32). 86

87

Externalizing scale

Internalizing scale

Psychosocial problem range

Externalizing behaviour

>3 hours per week

2-3 hours per week

<2 hours per week

Leisure time physical activity

Multiple risk behaviours

>7.9 hours

4.1-7.9 hours

0-4 hours

Total sitting time per day

8-9 hours

Sleeping time

Obese

Reference

overweight

BMI

Smoking

0.1-1.0 pack-years

non-regular smoker

obese normal weight

>9 hours

<8 hours

)LJ'LVWULEXWLRQRISV\FKRVRFLDODQGOLIHVW\OHIDFWRUVLQHDFKODWHQWFODVVDQDO\VLV/&$ FOXVWHUDPRQJJLUOV

0%

10 %

20 %

30 %

40 %

50 %

60 %

70 %

80 %

90 %

100 %

>1.0 pack-years

Externalizing scale

Internalizing scale

Psychosocial problem range

>3 hours per week

2-3 hours per week

<2 hours per week

Leisure time physical activity

Externalizing behaviour

>7.9 hours

4.1-7.9 hours

0-4 hours

Total sitting time per day

Reference

Obese

8-9 hours

Sleeping time

Sedentary

overweight

BMI

0.1-1.0 pack-years

Smoking

>1.0 pack-years

non-regular smoker

obese normal weight

<8 hours

)LJ'LVWULEXWLRQRISV\FKRVRFLDODQGOLIHVW\OHIDFWRUVLQHDFKODWHQWFODVVDQDO\VLV/&$ FOXVWHUDPRQJER\V

0%

10 %

20 %

30 %

40 %

50 %

60 %

70 %

80 %

90 %

100 %

>9 hours

88

7DEOH'HVFULSWLRQRIWKHSV\FKRVRFLDOFKDUDFWHULVWLFVRIWKH1)%&SRSXODWLRQ DW  \HDUV WKH SURSRUWLRQ   RI SUREOHP UDQJH YDOXHV RI WKH
YSR

Girls

Boys

Total

53%

47%

100%

(n = 3357)

(n = 3010)

(n = 6367)

% (n)

% (n)

% (n)

Syndrome Scales (1) Anxious/ depressed symptoms

6 (186)

3 (84)

4 (270)

(2) Withdrawn/ depressed symptoms

7 (241)

6 (186)

7 (427)

(3) Somatic complains

15 (509)

5 (149)

10 (658)

Social problems¹

4 (145)

3 (89)

4 (234)

Thought problems¹

4 (131)

2 (49)

3 (180)

Attention problems¹

8 (255)

3 (90)

5 (345)

(4) Rule-breaking behaviour

15 (512)

8 (254)

12 (766)

9 (292)

7 (213)

8 (505)

Internalizing problem range (1, 2, 3)

(5) Aggressive behaviour

19 (643)

11 (335)

15 (978)

Externalizing problem range (4, 5)

26 (864)

16 (469)

21 (1333)

¹ Subscales were not included in the studied problem scales.

89

7DEOH  'LVWULEXWLRQ RI /%3 DW  \HDUV LQ HDFK ODWHQW FODVV DQDO\VLV /&$  FOXVWHU DPRQJJLUOVLQWKH1)%&SRSXODWLRQ LCA clusters of girls Externalizing

Multiple risk

behaviour

behaviours

Obese

Reference

All

(n = 532) n (%)

(n = 421)

(n = 233)

(n = 2370)

(n = 3556)

n (%)

n (%)

n (%)

No LBP

n (%)

206 (39)

155 (37)

114 (49)

1324 (56)

1799 (51)

Reporting LBP¹

292 (55)

223 (53)

103 (44)

949 (40)

1567 (44)

Consultation for

34 (6)

43 (10)

16 (7)

97 (4)

190 (5)

LBP at 16 yrs.

LBP² p < 0.001 ¹ Reporting LBP indicates girls who reported having had LBP during the past 6 months, but had not consulted a health professional because of their LBP. ² Consultation for LBP indicates girls who reported having had LBP during the past 6 months, and had consulted a health professional because of their LBP.

7DEOH  'LVWULEXWLRQ RI /%3 DW  \HDUV LQ HDFK ODWHQW FODVV DQDO\VLV /&$  FOXVWHU DPRQJER\VLQWKH1)%&SRSXODWLRQ LCA clusters of boys Externalizing

Sedentary

Obese

Reference

All

(n = 871)

(n = 253)

(n = 1669)

(n = 3256)

behaviour (n = 463) LBP at 16 yrs.

n (%)

n (%)

n (%)

n (%)

n (%)

No LBP

230 (50)

573 (66)

163 (64)

1123 (67)

2089 (64)

Reporting LBP¹

201 (43)

266 (31)

81 (32)

474 (28)

1022 (31)

Consultation for

32 (7)

32 (4)

9 (4)

72 (4)

145 (5)

LBP² p < 0.001 ¹ Reporting LBP indicates boys who reported having had LBP during the past 6 months, but had not consulted a health professional because of their LBP. ² Consultation for LBP indicates boys who reported having had LBP during the past 6 months, and had consulted a health professional because of their LBP.

90

7DEOH3UHYDOHQFH RI/%3DW\HDUVLQHDFKODWHQWFODVVDQDO\VLV/&$ FOXVWHU DPRQJJLUOVZKRZHUHIUHHIURP/%3DW\HDUV¶1HZ/%3¶ LQWKH2%6SRSXODWLRQ LCA clusters of girls Externalizing

Multiple risk

behaviour

behaviours

Obese

Reference

All¹

(n = 62) % (n)

(n = 34)

(n = 35)

(n = 337)

(n = 468)

% (n)

% (n)

% (n)

No LBP

% (n)

37 (23)

38 (13)

46 (16)

53 (178)

49 (230)

Reporting LBP²

50 (31)

56 (19)

51 (18)

44 (147)

46 (215)

Consultation for LBP³

13 (8)

6 (2)

3 (1)

4 (12)

5 (23)

New LBP at 18 yrs.

¹ Girls who reported no LBP at 16 yrs. ² Reporting LBP indicates girls who reported having had LBP during the past 6 months, but had not consulted a health professional because of their LBP. ³ Consultation for LBP indicates girls who reported having had LBP during the past 6 months, and had consulted a health professional because of their LBP.

7DEOH3UHYDOHQFH RI/%3DW\HDUVLQHDFKODWHQWFODVVDQDO\VLV/&$ FOXVWHU DPRQJER\VZKRZHUHIUHHIURP/%3DW\HDUV¶1HZ/%3¶ LQWKH2%6SRSXODWLRQ LCA clusters of boys Externalizing

Sedentary

Obese

Reference

All¹

(n = 122)

(n = 26)

(n = 276)

(n = 462)

behaviour (n = 38) New LBP at 18 yrs.

% (n)

% (n)

% (n)

% (n)

% (n)

No LBP

61 (23)

63 (77)

81 (21)

64 (177)

65 (298)

Reporting LBP²

34 (13)

35 (43)

15 (4)

31 (86)

32 (146)

5 (2)

2 (2)

4 (1)

5 (13)

4 (18)

Consultation for LBP³

¹ Boys who reported no LBP at 16 yrs. ² Reporting LBP indicates boys who reported having had LBP during the past 6 months, but had not consulted a health professional because of their LBP. ³ Consultation for LBP indicates boys who reported having had LBP during the past 6 months, and had consulted a health professional because of their LBP.

91

7DEOH5HODWLYHULVN55 RI/%3DW\HDUVDFFRUGLQJWRHDFKFOXVWHURISRWHQWLDO SV\FKRVRFLDODQGOLIHVW\OHULVNIDFWRUVDPRQJJLUOVDW\HDUVFURVVVHFWLRQDODQDO\VLV RIWKH1)%&SRSXODWLRQ  Girls: LBP at 16 yrs.

RR

95% CI

cases/n

Reporting LBP¹ Externalizing behaviour

1.37

1.25–1.50

292/532

Multiple risk behaviours

1.32

1.19–1.47

223/421

Obese

1.10

0.95–1.29

Reference

1.00

103/233 949/2370

Consultation for LBP² Externalizing behaviour

1.56

1.07–2.28

34/532

Multiple risk behaviours

2.50

1.77–3.52

43/421

Obese

1.68

1.01–2.80

Reference

1.00

16/233 97/2370

¹ Reporting LBP indicates girls who reported having had LBP during the past 6 months, but had not consulted a health professional because of their LBP. ² Consultation for LBP indicates girls who reported having had LBP during the past 6 months, and had consulted a health professional because of their LBP.

7DEOH5HODWLYHULVN55 RI/%3DW\HDUVDFFRUGLQJWRHDFKFOXVWHURISRWHQWLDO SV\FKRVRFLDODQGOLIHVW\OHULVNIDFWRUVDPRQJER\VDW\HDUVFURVVVHFWLRQDODQDO\VLV RIWKH1)%&SRSXODWLRQ  Boys: LBP at 16 yrs.

RR

95% CI

cases/n

1.53

1.34–1.74

201/463 266/871

Reporting LBP¹ Externalizing behaviour Sedentary

1.08

0.95–1.22

Obese

1.13

0.93–1.37

Reference

1.00

81/253 474/1669

Consultation for LBP² Externalizing behaviour

1.60

1.07–2.40

32/463

Sedentary

0.85

0.57–1.28

32/871

Obese

0.82

0.42–1.63

Reference

1.00

9/253 72/1669

¹ Reporting LBP indicates boys who reported having had LBP during the past 6 months, but had not consulted a health professional because of their LBP. ² Consultation for LBP indicates boys who reported having had LBP during the past 6 months, and had consulted a health professional because of their LBP.

92

Table 31. Relative risk (RR) of LBP at 18 years according to each cluster of potential SV\FKRVRFLDODQGOLIHVW\OHULVNIDFWRUVDW\HDUVDPRQJJLUOVZKRZHUHIUHHIURP/%3 DW\HDUV¶1HZ/%3¶ $ORQJLWXGLQDODQDO\VLVRIWKH2%6FRKRUWDPRQJJLUOV Girls: New LBP at 18

RR

95% CI

cases/n

Externalizing behaviour

1.15

0.87–1.51

31/62

Multiple risk behaviours

1.28

0.93–1.77

19/34

Obese

1.18

0.84–1.66

Reference

1.00

Reporting LBP¹

18/35 147/337

Consultation for LBP² Externalizing behaviour

3.62

1.54–8.50

8/62

Multiple risk behaviours

1.65

1.39–7.08

2/34

Obese

0.80

0.11–5.99

Reference

1.00

1/35 12/337

¹ Reporting LBP indicates girls who reported having had LBP during the past 6 months, but had not consulted a health professional because of their LBP. ² Consultation for LBP indicates girls who reported having had LBP during the past 6 months, and had consulted a health professional because of their LBP.

Table 32. Relative risk (RR) of LBP at 18 years according to each cluster of potential SV\FKRVRFLDODQGOLIHVW\OHULVNIDFWRUVDW\HDUVDPRQJER\VZKRZHUHIUHHIURP/%3 DW\HDUV¶1HZ/%3¶ $ORQJLWXGLQDODQDO\VLVRIWKH2%6FRKRUWDPRQJER\V Boys: New LBP at 18

RR

95% CI

cases/n

Externalizing behaviour

1.10

0.68–1.76

13/38

Sedentary

1.13

0.84–1.52

32/122

Obese

0.49

0.20–1.24

Reference

1.00

Reporting LBP¹

4/26 86/276

Consultation for LBP² Externalizing behaviour

1.12

0.26–4.76

2/38

Sedentary

0.35

0.08–1.52

2/122

Obese

0.82

0.11–6.00

Reference

1.00

1/26 13/276

¹ Reporting LBP indicates boys who reported having had LBP during the past 6 months, but had not consulted a health professional because of their LBP. ² Consultation for LBP indicates boys who reported having had LBP during the past 6 months, and had consulted a health professional because of their LBP.

93

5.5

Summary of the main results of the thesis

7KHPDLQUHVXOWVRIWKHWKHVLVKDYHEHHQFROOHFWHGLQ7DEOHDQG0RGHUDWHDQG KHDY\ VPRNLQJ ZHUH DVVRFLDWHG ZLWK ³SHUVLVWHQW´ /%3 HTXDOO\ DPRQJ ERWK JHQGHUV $VIRUWKHQHZ/%3V\PSWRPVDW\HDUVSK\VLFDOZRUNORDGIDFWRUVFRQVLGHUHGDV SRWHQWLDOO\ VWUHQXRXV IRU WKH EDFN ZHUH DVVRFLDWHG ZLWK ³LQFLGHQW´ /%3 DPRQJ ERWK genders. In addition, psychosocial and lifestyle clusters including behavioural problems ZHUHDVVRFLDWHGZLWK/%3DW\HDUVDPRQJERWKJLUOVDQGER\V$VDZKROHPRUH associations were found among girls than boys including the accumulation of adverse psychosocial and lifestyle factors.

94

7DEOH  0DLQ UHVXOWV RI WKH WKHVLV DPRQJ JLUOV DGMXVWHG ULVN UDWLRV 55  RGGV UDWLRV 25  IRU WKH VWDWLVWLFDOO\ VLJQL¿FDQW DVVRFLDWLRQV IRXQG EHWZHHQ SRWHQWLDO ULVN GHWHUPLQDQWVDQG/%3³,QFLGHQW´/%3LQGLFDWHV/%3DW\HDUVDPRQJLQGLYLGXDOVIUHH IURP/%3DW\HDUV³3HUVLVWHQW´/%3LQGLFDWHV/%3DWERWKWLPHSRLQWV Girls

LBP at 16 yrs.

Potential risk determinants

“Incident”

“Persistent”

LBP

LBP

Overweight BMI from16 to18 yrs.

–

RR 1.1

Smoking Regular smoking

–

Moderate smoking¹

–

Heavy smoking²

–

OR 2.5 OR 1.8–2.4 OR 2.2–2.8

OR 2.6

Physical workload Working at 16 yrs.

–

RR 1.5

Duration of work (increment of 1 month)

–

RR 1.2

Awkward trunk postures, manual handling of

–

RR 1.2–1.3

–

RR 1.3–1.4

medium weight objects Clusters exposing to workload factors Family’s socioeconomic status Having self-employed parent

RR 1.1

RR 1.1

Having a student, unemployed, etc. parent

RR 1.4

Co-occurrence of psychosocial and lifestyle factors (clusters) Externalizing behaviour

RR 1.4–1.6

Multiple risk behaviours

RR 1.3–2.5

–

RR 1.7ª

–

Obese

RR 3.6ª

–

¹ Smoking 1–9 cig./day at 16 yrs./ 0.1–1.5 pack-years at 18 yrs. ² Smoking over 9 cig./day at 16 yrs./ over 1.5 pack-years at 18 yrs. ª LBP causing care seeking. BMI, body mass index.

95

7DEOH  0DLQ UHVXOWV RI WKH WKHVLV DPRQJ ER\V DGMXVWHG ULVN UDWLRV 55  RGGV UDWLRV 25  IRU WKH VWDWLVWLFDOO\ VLJQL¿FDQW DVVRFLDWLRQV IRXQG EHWZHHQ SRWHQWLDO ULVN GHWHUPLQDQWVDQG/%3³,QFLGHQW´/%3LQGLFDWHV/%3DW\HDUVDPRQJLQGLYLGXDOVIUHH IURP/%3DW\HDUV³3HUVLVWHQW´/%3LQGLFDWHV/%3DWERWKWLPHSRLQWV Boys

LBP at 16 yrs.

Potential risk determinants

“Incident”

“Persistent”

LBP

LBP

Overweight BMI from 7 to16 yrs.

–

RR 1.2

WC from 16 to 19 yrs.

–

RR 1.2

Smoking Regular smoking

–

Moderate smoking¹

–

Heavy smoking²

–

OR 2.1

OR 2.7–2.9 OR 2.5

Physical workload Awkward trunk postures, kneeling, working

–

RR 1.3–1.7

–

RR 1.6–1.9

hands above shoulders Clusters exposing to workload factors: Awkward trunk postures, physically demanding job Family’s socioeconomic status Co-occurrence of psychosocial and lifestyle factors (clusters) Externalizing behaviour

RR 1.5–1.6

¹ Smoking 1–9 cig./day at 16 yrs./ 0.1–1.5 pack-years at 18 yrs. ² Smoking over 1.5 pack-years at 18 yrs. BMI, body mass index; WC, waist circumference.

96

–



'LVFXVVLRQ



0DLQ¿QGLQJV

Reporting of LBP was common among adolescents in the current cohort, while VHHNLQJ FDUH IRU /%3 ZDV PRUH LQIUHTXHQW *LUOV UHSRUWHG PRUH /%3 DQG /%3 EHFDPHPRUHSUHYDOHQWZLWKDJH2IDGROHVFHQWVZLWKRXW/%3DW\HDUVKDOIRI WKHJLUOVDQGRQHWKLUGRIWKHER\VUHSRUWHG/%3DW\HDUVRIDJH $GROHVFHQWV¶%0,LQFUHDVHGZLWKDJH%0,IURPWR\HDUVLQJLUOVDQG %0, IURP  WR  \HDUV LQ ER\V ZDV DVVRFLDWHG ZLWK /%3 DW  \HDUV DPRQJ DGROHVFHQWV ZLWKRXW /%3 DW EDVHOLQH $PRQJ ER\V ZLWKRXW /%3 DW  \HDUV :& IURP  WR  \HDUV ZDV DVVRFLDWHG ZLWK /%3 DW  \HDUV7KH WLPH SHULRG during which overweight was related to new LBP was different between genders. 3HUVLVWHQWRYHUZHLJKWZDVQRWDVVRFLDWHGZLWK/%3DW\HDUVDPRQJDGROHVFHQWV UHSRUWLQJ/%3DWERWKEDVHOLQHDQGIROORZXS7KHDGMXVWPHQWIRUVPRNLQJOHLVXUH WLPHSK\VLFDODFWLYLW\DQGIDPLO\¶VVRFLRHFRQRPLFVWDWXVDW\HDUVRIDJHGLGQRW essentially alter the RR estimates for the associations found. )RXUWHHQSHUFHQWRIDGROHVFHQWVDWDQGHYHU\IRXUWKRIWKHPDW\HDUV RIDJHZHUHUHJXODUVPRNHUVDQGWKHDYHUDJHH[SRVXUHDW\HDUVZDVDERXWRQH SDFN\HDU5HJXODUVPRNLQJDW\HDUVZDVDVVRFLDWHGZLWK/%3DW\HDUVDPRQJ JLUOVUHSRUWLQJ/%3DWERWKWLPHSRLQWV$PRQJWKHVHJLUOVZLWK³SHUVLVWHQW´/%3 WKHUHZDVDQH[SRVXUHUHVSRQVHUHODWLRQVKLSZLWKWKHVPRNHGSDFN\HDUVDQG/%3 ZKHUHDVDPRQJER\VWKHDVVRFLDWLRQZDVLQFRQVLVWHQW7KHKHDYLHUWKHVPRNLQJ KLVWRU\ E\ SDFN\HDUV WKH KLJKHU WKH SUREDELOLW\ RI SHUVLVWHQW /%3 HVSHFLDOO\ DPRQJWKRVHZKRKDGVRXJKWPHGLFDOFDUH+HDY\VPRNLQJGDLO\VPRNLQJRIRYHU FLJDUHWWHVDW\HDUVDQGVPRNLQJH[SRVXUHRIPRUHWKDQSDFN\HDUVE\WKH DJHRI\HDUVZDVDVVRFLDWHGZLWKQHZ/%3DW\HDUVDPRQJJLUOVZLWKRXW/%3 at baseline. The analyses were adjusted for BMI, leisure time physical activity, depressive mood, and family’s socioeconomic status. 3DUWWLPH DQG SHULRGWLPH MREV ZHUH TXLWH FRPPRQ DPRQJ DGROHVFHQWV DQG DOPRVW WKUHH RXW RI IRXU DGROHVFHQWV ZLWKRXW /%3 DW  \HDUV RI DJH KDG EHHQ ZRUNLQJGXULQJWKHWZR\HDUWLPHFRXUVH7KHDYHUDJHGXUDWLRQRIZRUNZDVDERXW  PRQWKV:RUNLQJ UHJXODUO\ RU LUUHJXODUO\ DQG GXUDWLRQ RI ZRUN H[SRVXUH ZHUH DVVRFLDWHGZLWKQHZ/%3DW\HDUVDPRQJJLUOVLQLWLDOO\ZLWKRXW/%37KHZRUN H[SRVXUHSDWWHUQVLQJLUOVDQGER\VZHUHGLIIHUHQW2IVSHFL¿FSK\VLFDOZRUNORDG IDFWRUVRQO\DZNZDUGWUXQNSRVWXUHVZHUHDVVRFLDWHGZLWKQHZUHSRUWVRI/%3LQ 97

ERWKJHQGHUV$PRQJERWKJHQGHUVDFRPELQDWLRQRIZRUNORDGIDFWRUVH[SRVLQJ WRDZNZDUGWUXQNSRVWXUHVLQFOXGLQJW\SLFDOO\DOVRNQHHOLQJZRUNLQJZLWKKDQGV DERYHVKRXOGHUVDQGVWDQGLQJRUZDONLQJ DQGDFRPELQDWLRQRIRYHUDOOSK\VLFDOO\ GHPDQGLQJ MRE IDFWRUV ZHUH DVVRFLDWHG ZLWK QHZ /%3 DW  \HDUV 1RQH RI WKH VSHFL¿FZRUNORDGIDFWRUVRUWKHLUFRPELQDWLRQVZHUHDVVRFLDWHGZLWK³SHUVLVWHQW´ /%37KHVHDQDO\VHVZHUHDGMXVWHGIRU%0,OHLVXUHWLPHSK\VLFDODFWLYLW\VPRNLQJ and family’s socioeconomic status. )DPLO\¶VVRFLRHFRQRPLFVWDWXVZDVQRWDVVRFLDWHGZLWK/%3LQWKHIROORZXS with the exceptions of the daughters of self-employed parents and daughters of IDPLOLHVUHSRUWLQJµVRPHWKLQJHOVH¶HYHQDIWHUDGMXVWPHQWIRU%0,VPRNLQJDQG leisure time physical activity. In separate analyses among girls and boys, four clusters were found. More than half of the population belonged to a reference cluster with a low probability of psychosocial problems and unfavourable lifestyle factors. Behavioural problems predominated in one cluster and obesity in one cluster among both genders. The IRXUWK FOXVWHU DPRQJ ER\V ZDV FKDUDFWHUL]HG E\ VHGHQWDU\ OLIHVW\OH DQG DPRQJ JLUOV E\ PXOWLSOH ULVN EHKDYLRXUV 7KH FOXVWHUV LQFOXGLQJ EHKDYLRXUDO SUREOHPV ZHUH DVVRFLDWHG ZLWK /%3 DW  \HDUV DPRQJ ERWK JHQGHUV $PRQJ JLUOV WKH FOXVWHURIPXOWLSOHULVNEHKDYLRXUVZDVDVVRFLDWHGZLWKERWKµ5HSRUWLQJ/%3¶DQG µ&RQVXOWDWLRQ IRU /%3¶ DQG WKH REHVH FOXVWHU ZDV DVVRFLDWHG ZLWK µ&RQVXOWDWLRQ for LBP’ at baseline. The strongest association was found between the cluster of SUHGRPLQDWLQJEHKDYLRXUDOSUREOHPVDPRQJJLUOVDQGQHZ/%3ZLWKFDUHVHHNLQJ DW\HDUV7KHLQFOXVLRQRIIDPLO\¶VVRFLRHFRQRPLFVWDWXVDVDFRQIRXQGHUGLGQRW alter the results. In this thesis, more associations were found as a whole among girls than boys, DQG IRU QHZ WKDQ ³SHUVLVWHQW´ /%3 FDVHV ,Q WKH IROORZXS VPRNLQJ ZDV PRVW UHODWHG WR ³SHUVLVWHQW´ /%3 ZKLOH VPRNLQJ DQG SK\VLFDO ZRUNORDG IDFWRUV ZHUH most congruently related to new LBP among both genders. 

0HWKRGRORJLFDOFRQVLGHUDWLRQV

2QH ¿IWK RI WKH FRKRUW SRSXODWLRQ DW  \HDUV DQG RQH WKLUG RI WKH HOLJLEOH SRSXODWLRQ DW  \HDUV GLG QRW UHVSRQG WR WKH VXUYH\7KH UHVSRQVH SURSRUWLRQ LQ WKH EDVHOLQH ELUWK FRKRUW VWXG\ ZDV TXLWH KLJK DQG WKH GURSRXW UDWH ZDV LQ OLQH ZLWK SUHYLRXV VWXGLHV %RRNHU et al. 2011). The adolescents participated on a voluntary basis and received no compensation. Multiple postings of the TXHVWLRQQDLUHDQGWHOHSKRQHFDOOVZHUHXVHGWRJHWDQVZHUV7KHUHVSRQVHUDWHZDV 98

ORZHUDPRQJROGHUDGROHVFHQWVZKLFKLVLQOLQHZLWKSUHYLRXVVWXGLHV%RRNHU et al.  0DWWLOD HW DO   1RQHWKHOHVV WKHUH VHHPV WR EH QR PDUNHG VHOHFWLRQ ELDV EHWZHHQ WKH EDVHOLQH DQG \HDU UHVSRQGHQWV 7KH SDUWLFLSDQWV and non-respondents did not differ with respect to LBP. The respondents were PRUHOLNHO\OLYLQJLQWZRSDUHQWIDPLOLHVEXWRWKHUZLVHWKHUHZHUHQRVLJQL¿FDQW differences. There are no available data on non-responders in the baseline cohort DW  \HDUV$FFRUGLQJ WR SUHYLRXV QRUWKHUQ )LQODQG ELUWK FRKRUW  GDWD RQ \RXQJPDOHVQRQUHVSRQGHUVZHUHOHVVOLNHO\WRKDYHDWZRSDUHQWIDPLO\WKHLU IDPLO\¶V VRFLRHFRQRPLF VWDWXV ZDV PRUH OLNHO\ WR EH XQNQRZQ WKHLU VFKRRO SHUIRUPDQFHZDVSRRUHUWKDQDYHUDJHWKH\ZHUHPRUHOLNHO\VPRNLQJWHHQDJHUV DQGWKH\KDGVXIIHUHGIURPPHQWDOGLVRUGHUVPRUHRIWHQWKDQUHVSRQGHQWV3LHWLOl et al.1995). Unfortunately, non-respondents do not respond time-after-time in VXUYH\V3LHWLOlet al. 1995). Non-response may thus have caused some selection bias and it is possible that those who did not respond had a somewhat higher ULVN SUR¿OH WKDQ UHVSRQGHQWV DQG WKXV RXU UHVXOWV PD\ VOLJKWO\ XQGHUHVWLPDWH the true associations between the studied factors and LBP. The response rates of ER\VZHUHVOLJKWO\ORZHUFRPSDUHGWRJLUOV,QDGGLWLRQER\VGLGQRW¿OORXWWKH <65TXHVWLRQQDLUHDVWKRURXJKO\DVJLUOVDQGWKHPLVVLQJSV\FKRVRFLDOGDWDPD\ have caused underestimation of psychosocial problems among them. Immigrants DQG QHZO\ XUEDQL]HG LQGLYLGXDOV DUH SUREDEO\ XQGHUUHSUHVHQWHG LQ WKH VWXG\ SRSXODWLRQEXWRWKHUZLVHWKHUHVXOWVRIWKHVWXG\FDQZHOOEHJHQHUDOL]HGWRWKH QRUWKHUQ)LQQLVKDGROHVFHQWSRSXODWLRQ The outcome was self-reported LBP. LBP is always a personal and subjective experience, which is impossible to measure objectively. Thus, we do not have DEVROXWHVWDQGDUGVRIWKHGH¿QLWLRQIRU/%3DOWKRXJKVRPHUHFRPPHQGDWLRQVKDYH been made (Dionne et al.0LODQHVH *ULPPHU6RPHUV 7KHPLQLPDO GH¿QLWLRQ RI /%3 IRU ODUJH SRSXODWLRQEDVHG JHQHUDO VXUYH\V ZKLFK WKH 1)%& UHSUHVHQWVUHFRPPHQGVWKHXVHRIDORFDWLRQPDQLNLQ DQGWLPHIUDPHRI WKH SDLQ V\PSWRP DQG D TXHVWLRQ RQ VHYHULW\ RI /%3 'LRQQH et al.   $ PXVFXORVNHOHWDOSDLQPDQLNLQZDVXVHGLQWKHVWXG\EXWDOLPLWDWLRQZDVWKDWZH did not have a measure of activity limitations due to pain in our study. Instead, ZHDVNHGLILQGLYLGXDOVKDGFRQVXOWHGDKHDOWKSURIHVVLRQDOEHFDXVHRIWKHLU/%3 +RZHYHULWLVQRWHZRUWK\WKDWWKHFDUHVHHNLQJZDVVWURQJO\DVVRFLDWHGZLWK/%3 intensity and activity limitations in the same cohort population (Tiira et al. 2012). $VWKHRFFXUUHQFHRI/%3ZLWKFDUHVHHNLQJZDVORZZHFRXOGQRWXVHWKLVRXWFRPH LQ DOO VWXGLHV$ IXUWKHU OLPLWDWLRQ LV WKDW ZH GLG QRW DVN DERXW WKH IUHTXHQF\ RI WKH SDLQ HSLVRGHV RU SDLQ LQWHQVLW\ DQG WKH TXHVWLRQQDLUH GLG QRW VSHFL¿FDOO\ 99

differentiate menstruation pain from other types of pain in girls, which may partly H[SODLQWKHKLJKHUSUHYDOHQFHRIµ5HSRUWLQJ/%3¶LQJLUOV,QDGGLWLRQZHGLGQRW DVNSDUWLFLSDQWVWRRPLWSDLQGXHWRLQIHFWLRXVGLVHDVHIRUH[DPSOH)LQDOO\ZHGLG QRWKDYHDUHSURGXFLELOLW\VWXG\RIWKHPXVFXORVNHOHWDOSDLQTXHVWLRQQDLUHDWHLWKHU WLPHSRLQW:HDVNHGLIWKHDGROHVFHQWVKDGH[SHULHQFHG/%3GXULQJWKHSUHFHGLQJ  PRQWKV DQG WKH SRVVLELOLW\ RI UHFDOO ELDV VKRXOG EH NHSW LQ PLQG +RZHYHU DGROHVFHQWVVHHPWRUHPHPEHUWURXEOHVRPHEDFNV\PSWRPVEHWWHUDQGWKHRSWLPDO time frame for the pain is up to 12 months, after which memory loss begins to increase (Milanese & Grimmer-Somers 2010). We have used the term “incident /%3´LQRXUVWXG\EXWVWULFWO\VSHDNLQJWKHWHUP³LQFLGHQFH´LVPLVOHDGLQJDVWKH VXEMHFWVZKRGLGQRWUHSRUW/%3GXULQJWKHSDVWPRQWKVDW\HDUVRIDJHPD\ have experienced pain at an earlier time point or during the interval between the TXHVWLRQQDLUHV)XUWKHUPRUHDV ZH DQDO\VHGRQO\ WZR WLPHSRLQWV  \HDUV DSDUW ZHPD\QRWKDYHFDSWXUHGDOOWKH³LQFLGHQW´FDVHV6LPLODUO\³SHUVLVWHQFH´±WKDW LV/%3GXULQJWKHSDVWPRQWKDWDQG\HDUVRIDJH±LVQRWFRPSDUDEOHWR FKURQLF/%3+RZHYHU³UHFXUUHQW/%3´ZRXOGQRWKDYHEHHQDEHWWHUFKRLFHDVZH had only two assessment time points. The occurrence of LBP among adolescents LQWKLVFRKRUWLVLQOLQHZLWKSUHYLRXVVWXGLHV$XYLQHQ 7RVXPXSGHVSLWH VRPH OLPLWDWLRQV RI RXU SDLQ TXHVWLRQV DQG GDWD FROOHFWLRQ WKLV VWXG\ SUREDEO\ VXFFHHGHG LQ ¿QGLQJ DGROHVFHQWV VXIIHULQJ IURP JHQHUDO FKURQLFUHFXUUHQW DQG WUHDWPHQWUHTXLULQJVHYHUH /%3V\PSWRPV The results of the study relied on self-reported values of lifestyle (except BMI) and psychosocial factors, which is the usual method in population-based epidemiological studies, but prone to desirability bias. BMI values were also based RQ VHOIUHSRUWHG LQIRUPDWLRQ LQ WKH \HDU VXUYH\ :HLJKW LV SRWHQWLDOO\ XQGHU reported, more by girls and overweight adolescents, and height seems to be more often over-reported (Crawley & Portides 1995, Giacchi et al.   ,Q FDVH RI nondifferential misreporting, we might have underestimated the true connection of %0,DQG/%37KHGDWDRQZHLJKWUHODWHGPHDVXUHPHQWVZDVFROOHFWHGDW DQG\HDUVRIDJH7KHSHULRGVRIDJHVWRDQGDGROHVFHQFHKDYHEHHQUHFRJQL]HG as critical for abnormal weight gain (Daniels et al. 2005). In addition, boys may have PLVUHSRUWHGWKHLUVPRNLQJKDELWVLQWKHVDPHPDQQHUDVWKH\ZHUHPRUHFDUHOHVV with their reports on YSR compared to girls. However, some underreporting of VPRNLQJPD\H[LVWDPRQJERWKJHQGHUVDVVPRNLQJLVFRQVLGHUHGSRRUEHKDYLRXU DQGVHOOLQJDQGSURYLGLQJFLJDUHWWHVWRDGROHVFHQWVXQGHU\HDUVROGLVQRWOHJDOLQ )LQODQG&RPSDUHGWRRWKHUVWXGLHVFRQGXFWHGLQFODVVURRPVWKHDGROHVFHQWVLQRXU study may have felt it easier to give truthful answers at home, apart from authorities 100

DQGSHHUV0RUHRYHUWKHTXHVWLRQVRQVPRNLQJPD\KDYHEHHQTXLWHHDV\IRUWKH DGROHVFHQWVDVWKHTXHVWLRQQDLUHDOVRLQFOXGHGPRUHSULYDWHTXHULHVIRULQVWDQFH about stronger drugs and contraception. No accelerometer data or other objective PHDVXUHPHQWV DUH DYDLODEOH RQ WKH FRKRUW PHPEHUV¶ SK\VLFDO DFWLYLW\LQDFWLYLW\ HYHQWKRXJKVHOIUHSRUWLQJSK\VLFDODFWLYLW\PD\EHXQUHOLDEOH:HGGHUNRSSet al.  $GROHVFHQWVPD\KDYHRYHUUHSRUWHGWKHLUOHLVXUHWLPHSK\VLFDODFWLYLW\WR some extent to meet common health expectation. On the other hand, the method of combining different sedentary activities may have caused some over-reporting. However, it is common in population-based studies to use self-reported values to UHGXFH FRVWV DQG WR LPSURYH WKH SDUWLFLSDWLRQ UDWH:RUN H[SRVXUH ZDV DVVHVVHG UHWURVSHFWLYHO\$IXUWKHUOLPLWDWLRQLVWKDWZHGLGQRWDVVHVVSV\FKRORJLFDOIDFWRUV UHODWHG WR ZRUN ZKLFK KDYH EHHQ VKRZQ WR LQÀXHQFH /%3 /LQWRQ   /RZ EDFNV\PSWRPVDW\HDUVRIDJHPLJKWKDYHLQWURGXFHGVRPHELDVWRWKHUHSRUWLQJ RI ZRUNORDG +RZHYHU WKH DQVZHUV RQ ZRUNORDG ZHUH JHQHUDOO\ IDLUO\ GHWDLOHG DQG LW VHHPHG WR EH HDV\ IRU DGROHVFHQWV WR UHPHPEHU WKHLU ZRUNLQJ KLVWRU\$ VHOIDGPLQLVWHUHG TXHVWLRQQDLUH KDV EHHQ SURSRVHG WR EH XVHIXO LQ FODVVLI\LQJ KHWHURJHQHRXVRFFXSDWLRQDOWDVNVEXWTXHVWLRQQDLUHEDVHGDVVHVVPHQWRIZRUNORDG LV QRW VXI¿FLHQWO\ DFFXUDWH WR VWXG\ TXDQWLWDWLYH H[SRVXUHHIIHFW UHODWLRQVKLSV 9LLNDUL-XQWXUD et al. 7RWHVWWKHHIIHFWRIPXOWLSOHH[SRVXUHVRQ/%3ZH HPSLULFDOO\GHULYHGWKHSDWWHUQVRIFRRFFXUULQJH[SRVXUHVE\/&$DQGHVWLPDWHG WKHHIIHFWVRIWKHVHSDWWHUQVRQ/%3$OLPLWDWLRQRIWKHVHSDWWHUQVZDVWKDWZHZHUH QRWDEOHWRVSHFLI\ZKHWKHUWKHGLIIHUHQWZRUNH[SRVXUHVRFFXUUHGVLPXOWDQHRXVO\ RUGXULQJGLIIHUHQWZRUNLQJSHULRGV7KH)LQQLVKYHUVLRQRIWKH<65IRUHPRWLRQDO DQG EHKDYLRXUDO SUREOHPV ZDV XVHG LQ WKH VWXG\ 7KH <65 TXHVWLRQQDLUH LV D YDOLGDWHGUHOLDEOHDQGZLGHO\XVHGPXOWLGLPHQVLRQDOTXHVWLRQQDLUH$FKHQEDFK  5HVFRUOD+HLNNDODet al.,YDQRYDet al. $WWKHWLPHRIVWXG\,, we were forced to use data on self-reported depressive mood captured from a not HVWDEOLVKHGTXHVWLRQ The major strengths of the study are a large, population-based sample of QRUWKHUQ)LQQLVKDGROHVFHQWVDQGDORQJLWXGLQDOVWXG\GHVLJQ/RQJLWXGLQDOGHVLJQ allows catching up new LBP cases, follow-up of weight gain and other potential H[SRVXUHV DQG FRQWURO IRU SRWHQWLDO PRGLI\LQJ IDFWRUV LGHQWL¿HG DW EDVHOLQH 8QOLNH VHYHUDO SUHYLRXV VWXGLHV ZH FRQVLGHUHG IDPLO\¶V VRFLRHFRQRPLF VWDWXV V\VWHPDWLFDOO\ DV D SRVVLEOH FRQIRXQGHU$OO DQDO\VHV ZHUH SHUIRUPHG VHSDUDWHO\ IRUJLUOVDQGER\VEHFDXVHRIWKHPDUNHGGLIIHUHQFHVLQSDLQUHSRUWLQJDQGJURZWK patterns between genders. The gathered information covered a comprehensive set RI ERWK SV\FKRVRFLDO DQG OLIHVW\OH ULVN GHWHUPLQDQWV SRWHQWLDOO\ DVVRFLDWHG ZLWK 101

/%37KH ZRUNORDG ZDV DVVHVVHG ZLWK PRUH GHWDLOHG TXHVWLRQV WKDQ LQ SUHYLRXV VWXGLHV RI DGROHVFHQWV DQG H[SRVXUHV WR VKRUWWLPH MREV ZHUH DOVR HQTXLUHG We used a comprehensive set of potential psychosocial and lifestyle factors in FOXVWHULQJDQGWRRXUNQRZOHGJHIRUWKH¿UVWWLPHDQDO\VHGORQJLWXGLQDOO\ZKHWKHU the co-occurrence of these factors associates with LBP among adolescents. 

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6.3.1 Overweight 8QOLNHWRWKH¿QGLQJVRIWKHUHFHQWPHWDDQDO\VLV6KLUL et al. 2010a) consisting PDLQO\RIDGXOWSRSXODWLRQVRYHUZHLJKWVHHPHGWRDVVRFLDWHZLWK³LQFLGHQW´/%3 UDWKHUWKDQ³SHUVLVWHQW´/%3LQRXUFRKRUWRIDGROHVFHQWV,QFRKRUWVWXGLHVRIWKH previously mentioned meta-analysis, the OR for association between obesity and incident LBP was 1.5. In our study, the RRs of detected associations were rather ORZEXWWKH\VKRXOGEHYLHZHGLQUHODWLRQWRWLPHVSDQ)RUH[DPSOHLQJLUOV55  IRU WKH DVVRFLDWLRQ EHWZHHQ %0, IURP  WR  \HDUV DQG ³LQFLGHQW´ /%3 PHDQVWKDWXQLWULVHLQ%0,GXULQJWKDWWLPHVSDQLQFUHDVHGWKHULVNRI/%3E\ The evidence from previous studies among adolescents has been mainly negative +HVWEDHNet al.D-RQHVet al. 2003, Mustard et al. 2005). In our study, 3 out RISRVVLEOHDVVRFLDWLRQVIRU³LQFLGHQW´/%3ZHUHSRVLWLYHEXWRYHUZHLJKWZDV QRWDVVRFLDWHGZLWK³SHUVLVWHQW´/%32QHH[SODQDWLRQIRUWKHSRVLWLYHDVVRFLDWLRQ LQ FDVH RI ³LQFLGHQW´ EXW QRW ³SHUVLVWHQW´ /%3 FRXOG EH WKDW WKRVH DGROHVFHQWV ZKR UHSRUWHG /%3 DOUHDG\ DW  \HDUV LQFOXGLQJ VXEMHFWV ZLWK PRUH UHFXUUHQW symptoms), may be more prone to LBP due to other reasons. Previous LBP predicts IXWXUH/%3V\PSWRPV+HVWEDHNet al.E /%3DW\HDUVPD\DOVREHUHODWHG to early-onset DD, which has been related to LBP in adolescents (Salminen et al.   )XUWKHUPRUH HDUO\ RQVHW RI /%3 KDV EHHQ DVVRFLDWHG ZLWK SV\FKRVRFLDO factors (Watson et al.   SV\FKRVRPDWLF V\PSWRPV 9LNDW et al. 2000) and multiple pain symptoms (Salminen et al. 1992), especially among girls. In our cluster analyses, the obese cluster of girls was associated with µ&RQVXOWDWLRQ IRU /%3¶ DW EDVHOLQH +RZHYHU WKH DVVRFLDWLRQV ZHUH DOPRVW VWDWLVWLFDOO\ VLJQL¿FDQW EHWZHHQ µ5HSRUWLQJ /%3¶ DQG REHVH FOXVWHUV DPRQJ both genders in the aforementioned cross-sectional analyses. This is in line with the cross-sectional studies of the former meta-analysis, which concluded that association between prevalence of LBP and overweight or obesity was stronger 102

among females (Shiri et al.D )XUWKHUPRUHRXU¿QGLQJVZLWKFDUHVHHNLQJIRU LBP and obesity are in line with the meta-analysis. :HIRXQGWKDW:&ZDVDVVRFLDWHGZLWK³LQFLGHQW´/%3DPRQJER\VEXWQRW DPRQJ JLUOV 6KLUL DQG FRZRUNHUV   GHWHFWHG DOVR GLVVLPLODULWLHV EHWZHHQ JHQGHUVLQWKHLUVWXG\LQWKH
(Daniels et al. 2005, MacGregor et al. ,QWXUQLQFUHDVHG%0,VHHPHGWR SURWHFWDGROHVFHQWVIURPVSLQDOGHIRUPLWLHV+HUVKNRYLFKet al. ,WKDVEHHQ suggested that sedentary lifestyle could be associated with LBP (Chen et al. 2009). 2QHSRVVLEOHOLQNEHWZHHQKLJKOHYHOVRIVLWWLQJDQG/%3FRXOGEHREHVLW\EHFDXVH in a study among adults, overweight and obesity were related to high levels of sitting (Brown et al. 2003). In contrast, obesity and high levels of sitting predominated in different lifestyle clusters in our study. 6.3.2 Smoking $FFRUGLQJWRDUHFHQWUHYLHZRQVPRNLQJDQG/%3DZHDNSRVLWLYHDVVRFLDWLRQZLWK the prevalence and incidence of LBP was found and it was strongest for chronic or disabling symptoms (Shiri et al.E 2XU¿QGLQJVFRQFHUQLQJVPRNLQJDQG ³SHUVLVWHQW´ /%3 DUH LQ OLQH ZLWK WKH DERYHPHQWLRQHG UHYLHZ 0RVW FRPPRQO\ cohort studies among adolescents and young adults have reported ORs close to two EHWZHHQVPRNLQJDQG/%3)HOGPDQet al. 2001, Mustard et al.+HVWEDHN et al. D  2XU ¿QGLQJV RI WKH DPRXQW RI WKH DVVRFLDWLRQ DUH FRQVLVWHQW ZLWK these cohort studies. In our cohort, ORs for incident LBP were about two, but the DVVRFLDWLRQVZHUHVWURQJHUIRU³SHUVLVWHQW´/%3DQGIRU/%3FDXVLQJFDUHVHHNLQJ We did not estimate the duration of LBP. Instead, we evaluated the self-reported PRQWK SHULRG SUHYDOHQFH RI /%3 DW WZR VHSDUDWH WLPH SRLQWV 7KH FDVHV ZLWK ³SHUVLVWHQW´ /%3 UHSRUWLQJ V\PSWRPV DW WZR WLPH SRLQWV PD\ SHUKDSV UHSUHVHQW more chronic or recurrent LBP. The follow-up time of our study was not long but even so, the results of our study strengthen the evidence for the association between VPRNLQJDQG/%3GXULQJDGROHVFHQFH $JHQGHUGLIIHUHQFHZDVVHHQLQWKHDVVRFLDWLRQRIKHDY\VPRNLQJDQG³LQFLGHQW´ /%3 LQ RXU VWXG\ DV WKH DVVRFLDWLRQ ZDV RQO\ REVHUYHG LQ JLUOV$QRWKHU JHQGHU GLIIHUHQFHZDVVHHQLQWKHFXPXODWLYHDPRXQWRIVPRNLQJDQG/%3,WLVREYLRXV WKDW WKH ELRORJLFDO HIIHFWV RI VPRNLQJ DUH PRVWO\ VLPLODU IRU ERWK JHQGHUV 2QH SRVVLEOHEXWQRWYHU\OLNHO\H[SODQDWLRQFRXOGEHWKHKLJKHUSUHYDOHQFHRI/%3 among girls. In addition, boys may have underestimated their number of cigarettes. 0RUHRYHUVPRNLQJPD\EHOLQNHGZLWKGLVWUHVVRUDQ[LHW\HVSHFLDOO\DPRQJJLUOV $ SUHYLRXV VWXG\ DPRQJ VWXGHQWV UHSRUWHG WKDW /%3 ZDV PRUH SUHYDOHQW DPRQJ JLUOVDQGVPRNLQJZDVDVVRFLDWHGZLWKSV\FKRVRPDWLFV\PSWRPVLQFOXGLQJ/%3 RQO\LQJLUOV3LNR 1RHPL $ODUJHFURVVVHFWLRQDO&DQDGLDQVWXG\DPRQJ DGXOWVDOVRIRXQGWKDWHYHQRFFDVLRQDOVPRNLQJLQFUHDVHGWKHULVNRI/%3LQZRPHQ (but not in men) in the two youngest age groups (aged 20–29 and 30–39 years) 104

$ONKHUD\I et al.   7KH\ GH¿QHG /%3 DV H[SHULHQFLQJ V\PSWRPV IRU PRUH WKDQPRQWKVDQGEHLQJGLDJQRVHGE\DKHDOWKFDUHSURYLGHU 3URVSHFWLYHVWXGLHVRQVPRNLQJDQG/%3DPRQJDGROHVFHQWVDUHIHZ)HOGPDQ et al. 1999, Mustard et al.   )HOGPDQ DQG FRZRUNHUV   IRXQG WKDW DGROHVFHQW VPRNHUV UHSRUWHG LQFLGHQW /%3 PRUH WKDQ QRQVPRNHUV 0RUHRYHU WKH\IRXQGDQH[SRVXUHUHVSRQVHUHODWLRQVKLSEHWZHHQWKHDPRXQWVPRNHGDQGWKH QHZUHSRUWVRI/%3LQWKHIROORZXS7KH25LQWKHOLJKWWRPRGHUDWHVPRNHUV¶ JURXS ZDV  DQG LQ WKH KHDY\ VPRNHUV¶ JURXS  EXW WKH ODWWHU 25 ZDV QRW VWDWLVWLFDOO\ VLJQL¿FDQW7KHLU VWXG\ FRKRUW FRQVLVWLQJ RI DSSUR[LPDWHO\ \HDU old adolescents, was younger than our cohort, but the results of their study are FRQFRUGDQWZLWKRXU¿QGLQJV8QIRUWXQDWHO\WKH\UHSRUWHGWKHLQFLGHQFHRI/%3 combining girls and boys. The Canadian Ontario Child Health Study follow-up DOVR UHSRUWHG DQ DVVRFLDWLRQ ZLWK LQFLGHQW /%3 DQG SHUVLVWHQW KHDY\ VPRNLQJ DPRQJ \RXQJ DGXOWV DJHG ± \HDUV  0XVWDUG et al. 2005). In their cohort, LQFLGHQWFDVHVZHUHGH¿QHGDVUHVSRQGHQWVZKRUHSRUWHGWKHLU¿UVWHSLVRGHRI/%3 LQWKHSDVW\HDU7KH25RIKHDY\VPRNLQJZDVDQGFORVHWRRXUUHVXOWVHYHQ though their cohort was older. :HIRXQGWKDWKHDY\VPRNLQJZDVDVVRFLDWHGZLWKVHHNLQJFDUHIRU/%3DPRQJ DGROHVFHQWVZKRUHSRUWHG/%3DWERWKWLPHSRLQWV25VUDQJLQJIURPWR ,Q D ORQJWHUP IROORZXS RI DGXOW HPSOR\HHV KHDY\ VPRNLQJ LQFUHDVHG WKH ULVN RI KRVSLWDOL]DWLRQV IRU LQWHUYHUWHEUDO GLVF GLVHDVH RYHU WKUHHIROG .DLOD.DQJDV et al.   $PRQJ \RXQJ DGXOWV IRUPHU VPRNLQJ KDV EHHQ DVVRFLDWHG ZLWK KRVSLWDOL]DWLRQV IRU /%3 DQG VFLDWLFD 0DWWLOD et al.  5LYLQRMD et al. 2011). 2XU¿QGLQJVDUHLQOLQHZLWKWKHYLHZWKDWWKHFXPXODWLYHDPRXQWRIVPRNLQJLV LPSRUWDQWLQWKHH[SRVXUHDQGKHDY\VPRNLQJVHHPVWREHUHODWHGWRVHHNLQJFDUH for LBP. 7REDFFR VPRNH FRQWDLQV RYHU  FKHPLFDOV LQFOXGLQJ GR]HQV RI NQRZQ FDUFLQRJHQVWR[LFFKHPLFDOVDQGDGGLWLYHLQJUHGLHQWVZLWKSRRUO\NQRZQLQÀXHQFHV ZZZWULFRXQW\FHVVDWLRQRUJWREDFFRIDFWV&LJDUHWWH,QJUHGLHQWVKWPO 1LFRWLQHLV DGGLFWLYH HYHQ DPRQJ DGROHVFHQWV7KH SRWHQWLDO PHFKDQLVPV EHWZHHQ VPRNLQJ DQG /%3 DUH QRW ZHOO NQRZQ ,Q DQLPDO VWXGLHV QLFRWLQH KDV FDXVHG GHOHWHULRXV effects on the intervertebral disc tissue. Nicotine seems to inhibit proliferation of GLVF FHOOV DQG LV KDUPIXO IRU H[WUDFHOOXODU PDWUL[ V\QWKHVLV $NPDO et al.   $FXWHVPRNLQJUHVXOWHGLQDVLJQL¿FDQWUHGXFWLRQLQGLIIXVLRQRIVXOSKDWHR[\JHQ DQGPHWK\OJOXFRVHRIWKHSRUFLQHLQWHUYHUWHEUDOGLVF+ROP 1DFKHPVRQ  Nicotine exposure of rabbits resulted in vascular changes in the vicinity of the endplates and decreased the synthesis of proteoglycan and collagen in the nucleus 105

pulposus of the intervertebral disc (Iwahashi et al. ,QUDWVSDVVLYHVPRNLQJ caused changes in gene expression and later histological degenerative changes in the disc (Uei et al.   ,W LV WR EH QRWHG WKDW WKH KLVWRORJLFDO FKDQJHV LQ WKH annulus were partially irreversible whereas the changes in nucleus pulposus were reversible (Nemoto et al. ,QKXPDQVDVZHOOIRUPHUVPRNHUVKDGDORZHU ULVN RI FKURQLF /%3 RU VHHNLQJ FDUH IRU /%3 WKDQ FXUUHQW VPRNHUV 6KLUL et al. E 7KLVFRXOGLQGLFDWHWKDWVRPHHIIHFWVRIVPRNLQJPD\EHDWOHDVWSDUWLDOO\ UHYHUVLEOH DQG HQFRXUDJH VPRNHUV WR VWRS VPRNLQJ 6PRNHUV DUH PRUH OLNHO\ WR KDYHSDLQDWPXOWLSOHVLWHVRUZLGHVSUHDGSDLQWKDQQRQVPRNHUV$QGHUVVRQ et al. -RKQ et al.3DOPHU et al. 2003), which refers to more complex systemic HIIHFWVRIVPRNLQJ6PRNLQJPD\DOVRDIIHFWVHURWRQHUJLFV\VWHPVRIWKHFHQWUDO nervous system during adolescence (Xu et al. 2001, Xu et al. 2002) and predispose WR GHSUHVVLRQ DQG SDLQ V\PSWRPV 6PRNLQJ DOVR DIIHFWV WKH OHYHOV RI FLUFXODWLQJ SURLQÀDPPDWRU\ F\WRNLQHV ZKLFK PD\ DFW DV PHGLDWRUV LQ SDLQ SHUFHSWLRQ (O’Loughlin et al.  :DWNLQV  0DLHU 
UHODWLRQ WR WKH VSHFL¿F H[SRVXUHV RQO\ DZNZDUG WUXQN SRVWXUHV ZHUH DVVRFLDWHG ZLWK ³LQFLGHQW´ /%3 DPRQJ ERWK JHQGHUV ZLWK DGMXVWHG 55V RI  DQG  &RQFHUQLQJWKHDPRXQWRIWKHDVVRFLDWLRQEHWZHHQZRUNH[SRVXUHDQG/%3DPRQJ adolescents, our results are in line with previous studies, which have presented DGMXVWHG25VIURPWR)DVVDet al.)HOGPDQet al.)HOGPDQet al. 2002, Harreby et al. 1999, Jones et al. 2003, Watson et al. 2003). ,Q VSLWH RI VRPH PHWKRGRORJLFDO GLIIHUHQFHV RXU ¿QGLQJV DUH LQ OLQH ZLWK SUHYLRXV VWXGLHV DPRQJ DGROHVFHQWV 0RQRWRQRXV ZRUN DQG DZNZDUG SRVWXUHV ZHUH DVVRFLDWHG ZLWK EDFN SDLQ DPRQJ \RXQJ DGROHVFHQWV LQ D %UD]LOLDQ ORZ LQFRPHDUHD)DVVD et al. 2005). However, our study was conducted in different FRQGLWLRQV:RUNLQJGXULQJWKHVFKRRO\HDUEXWQRWLQWKHKROLGD\VHDVRQVHHPHG to be associated with the development of LBP among high school students )HOGPDQ et al.)HOGPDQ et al. :HGLGQRWDVNLIZRUNWRRNSODFH during the school year or during holidays. In their study, the development of PXVFXORVNHOHWDOV\PSWRPVZDVKLJKHVWLQZKLWHFROODUZRUNIROORZHGE\EOXH FROODUZRUNDQGORZHVWLQFKLOGFDUHZRUN)HOGPDQ et al. 2001). In our cohort, WKHRFFXSDWLRQVDQGZRUNH[SRVXUHSDWWHUQVLQJLUOVDQGER\VZHUHGLIIHUHQWDQG ZH SUHIHUUHG WR PDNH WKH DQDO\VHV VHSDUDWHO\ IRU ERWK JHQGHUV 7KH WZR PRVW FRPPRQ RFFXSDWLRQV IRU JLUOV ZHUH JDUGHQLQJIDUP ZRUN DQG FOHDQHU LQ WKH DZNZDUG SRVWXUHV FOXVWHU DQG JDUGHQLQJIDUP ZRUN DQG VKRS DVVLVWDQW LQ WKH physically demanding cluster. In both of these two clusters among boys, property PDLQWHQDQFHJDUGHQLQJDQGFRQVWUXFWLRQZRUNZHUHWKHPRVWFRPPRQO\UHSRUWHG occupations. ,QDVWXG\RQ\RXQJZRUNHUV¿UVWHYHUHSLVRGHVRI/%3ZHUHDVVRFLDWHGZLWK VHDWHGZRUNÀH[LRQRUURWDWLRQPRYHPHQWVRIWKHWUXQNDQGZRUNLQYROYLQJKHDY\ lifting for several years (Van Nieuwenhuyse et al.   :KLOH SDUWLFLSDQWV LQ WKHLUVWXG\ZHUH\RXQJDGXOWVZRUNLQJLQWHQXUHGSRVLWLRQVDQGPRVWO\IXOOWLPH DGROHVFHQWV LQ RXU VWXG\ KDG PRVWO\ SDUWWLPH MREV DQG VKRUWHU ZRUNLQJ KLVWRU\ 1RQHWKHOHVVZHDOVRIRXQGDQDVVRFLDWLRQEHWZHHQDZNZDUGWUXQNSRVWXUHVDQG ³LQFLGHQW´/%3 (YHQ WKRXJK +DUUHE\ DQG FRZRUNHUV   UHSRUWHG DVVRFLDWLRQV EHWZHHQ UHFXUUHQWFRQWLQXRXV /%3 V\PSWRPV H[SHULHQFHG DV PRGHUDWHVHYHUH DQG KHDY\ ZRUNZHIRXQGQRDVVRFLDWLRQVEHWZHHQFRPELQHGSK\VLFDOZRUNORDGIDFWRUVDQG /%3DPRQJ³SHUVLVWHQW´FDVHV:HFRXOGQRW¿QGDQ\LQGLFDWLRQVIRUVHOHFWLRQELDV ,WLVPRUHOLNHO\WKDWSUHYLRXV/%3SUHGLVSRVHGIRU/%3DWIROORZXSDVSUHYLRXV VWXGLHVKDYHLQGLFDWHG+HVWEDHN et al.E6MROLH $OVRWKHUROHRIJHQHWLF RUXQNQRZQHQYLURQPHQWDOIDFWRUVPD\EHPRUHLPSRUWDQWLQWKLVJURXSZLWKHDUO\ 107

symptoms of LBP. Unfortunately, we had too few cases in the clusters so we were QRWDEOHWRDQDO\VH/%3ZLWKFDUHVHHNLQJVHSDUDWHO\ $ V\VWHPDWLF UHYLHZ FRQFOXGHG WKDW WKH HYLGHQFH RQ DQ DVVRFLDWLRQ EHWZHHQ KHDY\SK\VLFDOZRUNDQG/%3LVFRQÀLFWLQJ%DNNHU et al. 2009). There is controversy UHJDUGLQJ WKH ZRUNUHODWHGQHVV RI /%3 GXH WR RFFXSDWLRQDO OLIWLQJ DQG DZNZDUG postures (Kuijer et al. 2011, Roffey et al. 2010, Wai et al. 2010). However, one UHYLHZIRXQGPRGHUDWHHYLGHQFHIRUKHDY\SK\VLFDOZRUNDOWKRXJKWKHDVVRFLDWLRQ was attenuated in the sensitivity analysis (Hoogendoorn et al. 1999). In addition, DQRWKHU PHWDDQDO\VLV IRXQG WKDW DZNZDUG SRVWXUHV DQG PDQXDO KDQGOLQJ ZHUH UHODWHGWR/%3*ULI¿WKet al. 2012). Whole body vibration has also been related to LBP (Hoogendoorn et al. 1999). In this study, the proportion of those with multiple H[SRVXUHVDQGWKRVHH[SRVHGWRVWUHQXRXVZRUNZDVUDWKHUORZ(YHQWKRXJKWKH ZRUN H[SRVXUH XVXDOO\ FRQVLVWHG RI VHYHUDO VHSDUDWH HSLVRGHV ZH REVHUYHG DQ DVVRFLDWLRQHVSHFLDOO\EHWZHHQDZNZDUGWUXQNSRVWXUHVDQG³LQFLGHQW´/%3,QRXU study, the exposure to whole body vibration by driving was not associated with LBP. It is noteworthy that the driving exposure was very low in this young cohort DQGWKHUHIRUHZHFDQQRWGUDZDQ\FRQFOXVLRQVDERXWWKHDVVRFLDWLRQLQTXHVWLRQ$ V\VWHPDWLFUHYLHZIRXQGVRPHDVVRFLDWLRQVEHWZHHQSV\FKRVRFLDOIDFWRUVDWZRUN and LBP (Hoogendoorn et al. $OLPLWDWLRQRIRXUVWXG\ZDVWKDWHYHQWKRXJK ZHJDWKHUHGGHWDLOHGGDWDRQSK\VLFDOZRUNORDGIDFWRUVZHGLGQRWDVVHVVZRUN related psychological factors. There is controversy regarding the effect of physical loading on the lumbar VSLQH VR WKDW KHDY\ SK\VLFDO ORDGLQJ DW ZRUN LV UHJDUGHG DV KDUPIXO ZKHUHDV physical activity in leisure time it is thought to promote health (Battie et al. Kujala et al. 7KHUHODWLRQVKLSEHWZHHQSK\VLFDODFWLYLW\DQG/%3LVWKRXJKW to be U-shaped (Heneweer et al. 2009). However, objectively measured physical DFWLYLW\ZDVQRWDVVRFLDWHGZLWK/%3DPRQJDGROHVFHQWV:HGGHUNRSSet al. 2003). $PRQJ DGROHVFHQWV D YHU\ KLJK OHYHO RI SK\VLFDO DFWLYLW\ DVVRFLDWHG ZLWK /%3 $XYLQHQ et al. DQGKRVSLWDOL]DWLRQV0DWWLOD et al. ,QRXUDQDO\VHVZH used the adjustment for the self-reported amount of leisure time physical activity DQGVPRNLQJ What could be the mechanism of the observed association between the UHODWLYHO\ VKRUW H[SRVXUH WR SK\VLFDO ZRUN DQG /%3 LQ DGROHVFHQFH" 0DQXDO PDWHULDOVKDQGOLQJDQGDZNZDUGSRVWXUHVPD\OHDGWRIDWLJXHDQGIDLOXUHRIOXPEDU tissues (Mehta et al. RUWKHUHSRUWHGSDLQV\PSWRPVPD\UHÀHFWVRPHWKLQJ else than serious tissue pathology.

108

6.3.4 Socioeconomic factors Previous research has documented that low socioeconomic status is associated with many health problems in childhood (Spencer et al. 2013) and with unhealthy EHKDYLRXUVDQGPDQ\GLVHDVHVLQDGXOWKRRG+DQVRQ &KHQ ,QDGROHVFHQFH WKHVHDVVRFLDWLRQVVHHPQRWDVUREXVWDVWKHLQÀXHQFHRIIULHQGV\RXWKFXOWXUHDQG VFKRROHQYLURQPHQWEHFRPHVPRUHLPSRUWDQW+DQVRQ &KHQ 7KHHYLGHQFH RQ/%3LQDGROHVFHQFHLVVWLOOFRQÀLFWLQJ+HVWEDHNet al./HERHXI
LQVWDQFHSDUHQWV¶HGXFDWLRQRFFXSDWLRQIDPLO\¶VLQFRPHKRXVHKROGZRUNOHVVQHVV family’s wealth and material resources, and the adolescent’s opportunity to spend money have been used, either separately or in combination, in studies among DGROHVFHQWV +DQVRQ  &KHQ  6SHQFHU   ,Q WKLV VWXG\ ZH XVHG D TXHVWLRQQDLUH EDVHG RQ RFFXSDWLRQDO SRVLWLRQ $ ORZHU VRFLRHFRQRPLF VWDWXV LQ DGROHVFHQFH KDV EHHQ OLQNHG WR SV\FKRORJLFDO SUREOHPV GLI¿FXOWLHV ZLWK VFKRRO SRRU GLHW LQDFWLYLW\ DQG VPRNLQJ +DQVRQ  &KHQ   7KH DIRUHPHQWLRQHG literature review indicated also that high, and not only low, socioeconomic status may be related to some negative health behaviours among adolescents, including VXEVWDQFHDEXVHDQGJUHDWHUSV\FKRVRFLDOVWUHVV+DQVRQ &KHQ $QHZO\ published meta-analysis concluded that subjective socioeconomic status was associated with adolescent health, including mental health, self-related health, DQG JHQHUDO KHDOWK V\PSWRPV 4XRQ  0F*UDWK   7KH GLIIHUHQW PHWKRGV IRU GH¿QLQJ VRFLRHFRQRPLF VWDWXV KDYH UHYHDOHG GLIIHUHQW DVVRFLDWLRQV GXULQJ adolescence. 6.3.5 Clustering of psychosocial and lifestyle factors Previous studies have shown accumulation of unhealthy behaviours among adults /DDNVRQHQ et al. 2001, Schuit et al. 2002) and adolescents (Leech et al.  Mistry et al.5DLWDNDULet al. 3UHYLRXVO\/&$KDVEHHQXVHGDPRQJ adolescents for instance to reveal patterns of physical activity and sedentary behaviour (Lajunen et al. VPRNLQJ*XRet al. 2009), and emotional (van Lang et al.   DQG EHKDYLRXUDO SUREOHPV /DFRXUVH et al.  $ SUHYLRXV VWXG\DPRQJ86XQLYHUVLW\VWXGHQWVFRQVLGHUHGDZLGHUDQJHRIULVNEHKDYLRXUVDQG OLIHVW\OHFKDUDFWHULVWLFVDQGIRXQGGLIIHUHQWFODVVHVIRUIHPDOHVDQGPDOHV/DVNDet al. 7KH\LGHQWL¿HGFODVVHVRIULVNDVVRFLDWHGEHKDYLRXUVVXFKDVGLHW SK\VLFDODFWLYLW\VWUHVVVOHHSDQGULVN\EHKDYLRXUV IRUERWKJHQGHUV,QOLQHZLWK WKHLUVWXG\ZHIRXQGGLIIHUHQWFOXVWHUVRISRWHQWLDOULVNIDFWRUVEHWZHHQJHQGHUVLQ RXUFRKRUW:HLGHQWL¿HGIRXUFOXVWHUVRISV\FKRVRFLDODQGOLIHVW\OHSDWWHUQVDPRQJ both genders. Most of the adolescents were allocated to the reference clusters ZLWK D ORZ SUREDELOLW\ RI H[SRVXUHV$GROHVFHQWV VHHPHG WR KDYH VRPH KHDOWK\ and unhealthy behaviours concurrently. In both genders, behavioural problems SUHGRPLQDWHG LQ RQH VXEJURXS DQG REHVLW\ LQ RQH VXEJURXS )XUWKHUPRUH ER\V KDGDVHGHQWDU\DQGJLUOVDPXOWLSOHULVNVXEJURXS,QFRQWUDVWWRWKLVVWXG\PRVW RI WKH VWXGLHV FRQGXFWHG KDYH LQYHVWLJDWHG D OLPLWHG QXPEHU RI SRWHQWLDO ULVN IDFWRUV ZLWKRXW WDNLQJ LQWR DFFRXQW ERWK SV\FKRVRFLDO DQG OLIHVW\OH SHUVSHFWLYHV 110

$ FURVVVHFWLRQDO VWXG\ DPRQJ HDUO\ DGROHVFHQWV IRXQG D WKUHHFODVV PRGHO IRU PXVFXORVNHOHWDO SDLQV $GDPVRQ et al.   6'4 VFRUHV DQG KHDGDFKHV ZHUH VLJQL¿FDQW IRU WKH ³%DFN DQG QHFN´ FODVV RI WKHLU VWXG\ 7R RXU NQRZOHGJH WKH SUHVHQWVWXG\LVWKH¿UVWWRHYDOXDWHDOVRWKHEDVHOLQHFOXVWHULQJRISV\FKRVRFLDODQG lifestyle factors in future adolescent LBP. Previous longitudinal studies among adolescents have revealed that psychosocial IDFWRUVVHHPWRDVVRFLDWHZLWK/%3%UDWWEHUJ-RQHVet al. 2003, Mustard et al. 6]SDOVNLet al. -RQHVDQGFRZRUNHUV ZHUHWKH¿UVWWRH[DPLQH if the mechanical and psychosocial factors associate with new onset of LBP in the ORQJLWXGLQDO VWXG\ VHWWLQJ 7KH\ IRXQG WKDW SV\FKRVRFLDO GLI¿FXOWLHV HVSHFLDOO\ conduct problems, were associated with new LBP during early adolescence with the TXLWHKLJK55RI7KH\PDGHWKHDQDO\VHVIRUJLUOVDQGER\VFRPELQHGDGMXVWLQJ WKHUHVXOWVIRUDJHDQGJHQGHU'HVSLWHPHWKRGRORJLFDOGLIIHUHQFHVRXU¿QGLQJVDUH SDUWO\FRQVLVWHQWZLWKWKHLUVWXG\:HREVHUYHGWKDWJLUOVLQWKHFOXVWHUFKDUDFWHUL]HG E\SV\FKRVRFLDOSUREOHPVZHUHPRVWDWULVNIRUQHZ/%3ZLWKFDUHVHHNLQJ7KH\ UHSRUWHG/%3ZLWKFDUHVHHNLQJDOPRVWIRXUWLPHVPRUHWKDQJLUOVLQWKHUHIHUHQFH FOXVWHU ,Q FRQWUDVW WKH DVVRFLDWLRQ ZDV QRW VHHQ DPRQJ JLUOV LQ WKH PXOWLSOH ULVN EHKDYLRXUV FOXVWHU *LUOV LQ WKHVH WZR FOXVWHUV VHHPHG WR KDYH TXLWH VLPLODU SV\FKRVRFLDOV\PSWRPVEXWJLUOVLQWKHH[WHUQDOL]LQJEHKDYLRXUFOXVWHUVDWOHVVDQG were physically more active. It is possible that their active lifestyle, combined with WKHLU UXOHEUHDNLQJ DQG PRUH DJJUHVVLYH QDWXUH PD\ SUHGLVSRVH WKHP IRU LQVWDQFH WR LQMXULHV EXW DOVR VWLPXODWH WKHLU DFWLYLW\ WR VHHN WUHDWPHQW 7KLV LV OLQH ZLWK D SUHYLRXVUHSRUWZKLFKIRXQGWKDWKLJKSK\VLFDODFWLYLW\DVVRFLDWHGZLWKFDUHVHHNLQJ IRUPXVFXORVNHOHWDOSUREOHPVDPRQJJLUOVLQWKLV2%6FRKRUW3DDQDQHQet al. 2011). ,QWKHFURVVVHFWLRQDODQDO\VHVRIWKHSUHVHQWVWXG\FOXVWHUVFKDUDFWHUL]HGE\ EHKDYLRXUDOSUREOHPVZHUHDVVRFLDWHGZLWK/%3DPRQJERWKJHQGHUV7KLV¿QGLQJ is in line with a cross-sectional Swiss study among children, which found an association between self-reported psychosocial strain, objective stress caused by educational selection and LBP (Erne & Elfering 2011). Numerous studies among adolescents have established the relationships between health behaviours and LBP (Jones & Macfarlane 2005). The main categories of the PRVWFRPPRQO\VWXGLHGKHDOWKEHKDYLRXUVLQFOXGHSK\VLFDODFWLYLW\LQDFWLYLW\DQG ERG\ PDVV LQGH[ -RQHV  0DFIDUODQH   6PRNLQJ VHHPV WR EH DVVRFLDWHG with adolescent LBP at least moderately according to previous studies and our RZQ¿QGLQJV)HOGPDQ et al. 1999, Mustard et al. $PRQJDGXOWVVPRNLQJ was reported to associate positively with all other included unhealthy behaviours /DDNVRQHQet al. 2001). On the other hand, there is evidence that stress, peers and 111

IDPLO\LQÀXHQFHDQGGHSUHVVLRQDUHULVNIDFWRUVIRUVPRNLQJDPRQJDGROHVFHQWV 6FKHSLV 5DR $VUHJDUGVSK\VLFDODFWLYLW\LQDFWLYLW\WKHDVVRFLDWLRQZLWK /%3LVPRUHFRQWURYHUVLDO$XYLQHQ et al.%DODJXp et al.:HGGHUNRSS et al.  $PRQJ \RXQJ DGXOWV DQ LQWHUDFWLRQ EHWZHHQ REHVLW\ DQG SK\VLFDO DFWLYLW\ZDVREVHUYHGDVORZOHYHORISK\VLFDODFWLYLW\LQFUHDVHGWKHULVNRIUDGLDWLQJ LBP among obese, but not overweight, individuals (Shiri et al. 2013). In our study, adolescents in the obese cluster did not have a very unhealthy lifestyle and only WKHREHVHFOXVWHURIJLUOVZDVDVVRFLDWHGZLWK/%3$FFRUGLQJWRRXUUHVXOWVFR occurrence of adverse lifestyle factors was associated with LBP at baseline among girls. The accumulating factors among these girls were a low level of leisure time SK\VLFDO DFWLYLW\ KLJK VLWWLQJ WLPH VPRNLQJ DQG XQIDYRXUDEOH VOHHSLQJ WLPH together with psychosocial problems. The associations found for multiple lifestyle factors seemed to be stronger than previous observations on single determinants. None of the clusters among boys associated with new LBP during the followup. These differences between genders may be due to the greater prevalence of VPRNLQJ DQG SV\FKRVRFLDO SUREOHPV DPRQJ JLUOV ,Q WXUQ WKH DPRXQW RI ER\V UHSRUWLQJµ&RQVXOWDWLRQIRU/%3¶DW\HDUVZDVORZZKLFKDIIHFWHGWKHSRZHURI WKHWHVWRIVLJQL¿FDQFH$IWHUDOOWKHREVHUYHGUHODWLRQVKLSEHWZHHQWKHH[WHUQDOL]LQJ EHKDYLRXUFOXVWHUVDQG/%3LQGLFDWHVWKDWEHKDYLRXUDOSUREOHPVDUHDNH\ULVNIDFWRU LQWKHVHFOXVWHUV2XU¿QGLQJVVWUHVVWKHVLJQL¿FDQFHRIHPRWLRQDODQGEHKDYLRXUDO SUREOHPVLQOLQHZLWKWKHFRQFOXVLRQVRI:DWVRQDQGFRZRUNHUV  'D\WLPH WLUHGQHVV DQG LQVXI¿FLHQW VOHHS KDYH SUHYLRXVO\ EHHQ DVVRFLDWHG ZLWK /%3 DQG PXVFXORVNHOHWDO SDLQV DPRQJ DGROHVFHQWV $XYLQHQ et al. 2010, 0LNNHOVVRQ et al.:DWVRQ et al. 2003). On the other hand, chronic insomnia has been related to psychological and interpersonal problems among adolescents (Roberts et al.   2XU ¿QGLQJV LQ WKH FOXVWHULQJ UHIHUUHG WR D PRUH FRPSOH[ relationship, but we considered both short and long sleeping times. In addition, the relation of physical inactivity and emotional and behavioural problems, which has previously been documented (Kantomaa et al. GLGQRWDSSHDUFRQVLVWHQWO\ in our study. 

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Previously, there were only few prospective studies on LBP and psychosocial and lifestyle factors among adolescents. This study was conducted in the phase ZKHQ WKH FRKRUW DGROHVFHQWV EHJDQ WR WDNH PRUH UHVSRQVLELOLW\ IRU WKHLU RZQ KHDOWK EHKDYLRXUV DQG HQWHUHG WR ZRUNLQJ OLIH 'HVSLWH VRPH PHWKRGRORJLFDO 112

challenges with grading LBP and the use of mostly self-reported data, the study offers comprehensive population-based information on a common condition with a ORQJLWXGLQDOGHVLJQ,QWHUHVWLQJO\ZHIRXQGGLVFUHSDQFLHVLQWKH¿QGLQJVEHWZHHQ genders throughout the study, the associations found being often stronger among girls than boys. The strength of detected associations between overweight and LBP were subtle but detectable during the developmentally important period covering the latest part RIPDWXUDWLRQ,QOLJKWRIRXU¿QGLQJVRYHUZHLJKWGXULQJDGROHVFHQFHVKRXOGEH considered as a determinant for LBP in future studies. Our study also strengthens WKH HYLGHQFH RI WKH FRQQHFWLRQ EHWZHHQ VPRNLQJ DQG /%3 DPRQJ DGROHVFHQWV $PRQJ WKH IDFWRUV H[DPLQHG WKH DVVRFLDWLRQ EHWZHHQ KHDY\ VPRNLQJ DQG /%3 ZDVWKHVWURQJHVW6PRNLQJLVGH¿QLWHO\DPRGL¿DEOHKHDOWKEHKDYLRXUDQGPXFK KDV EHHQ GRQH DW FRPPXQLW\ OHYHO WR GHFUHDVH VPRNLQJ$W WKH LQGLYLGXDO OHYHO this information about adverse health effects arising already in the short term may KHOSDGROHVFHQWVWRTXLWVPRNLQJDQGUHPDLQDQRQVPRNHU7KHSRVVLEOHEHQH¿FLDO HIIHFW RI VPRNLQJ FHVVDWLRQ RQ IXWXUH /%3 V\PSWRPV VKRXOG EH DGGUHVVHG LQ IXWXUH LQWHUYHQWLRQ WULDOV 2XU VWXG\ DSSHDUV WR EH WKH ¿UVW RQH WR DQDO\VH WKH DVVRFLDWLRQV RI VSHFL¿F SK\VLFDO ZRUNORDG H[SRVXUHV DQG FRPELQDWLRQV RI WKHP with the development of LBP in this age group. The results of this study suggest WKDW SK\VLFDO ZRUNORDG IDFWRUV PD\ EH KDUPIXO IRU EDFNUHODWHG ZHOOEHLQJ HYHQ DPRQJDGROHVFHQWVDQGZHVKRXOGWDNHFDUHRIWKHZRUNLQJFRQGLWLRQVRI\RXQJ ZRUNHUV6WLOOIXUWKHUVWXGLHVDUHQHHGHGWRDVVHVVDOVRZRUNUHODWHGSV\FKRORJLFDO IDFWRUVDPRQJ\RXQJZRUNHUV The determinants of LBP are multidimensional. The psychosocial and lifestyle factors included formed clusters already at an early age. The present study is WKH ¿UVW WR ORQJLWXGLQDOO\ DQDO\VH WKH SRVVLEOH DVVRFLDWLRQV EHWZHHQ EDVHOLQH FOXVWHUV RI WKHVH IDFWRUV DQG IXWXUH /%3 DPRQJ DGROHVFHQWV 2XU ¿QGLQJV VWUHVV the role of psychosocial factors in LBP, and may provide potential pathways for PXOWLGLVFLSOLQDU\ /%3 LQWHUYHQWLRQV DPRQJ DGROHVFHQWV VHHNLQJ FDUH IRU WKHLU V\PSWRPV (YHQ WKRXJK VRPH TXLWH FRPPRQ IDFWRUV IRU H[DPSOH HPRWLRQDO behavioural and sleeping problems or sedentary lifestyle, are not easy to LQÀXHQFHZHKRSHWKDWWKH\FDQEHPRGL¿HGDWOHDVWWRVRPHH[WHQWIRUH[DPSOH E\ VFKRROZRUN VFKHGXOLQJ KHDOWK SURPRWLRQ RU FRPPXQLW\ VXSSRUW7R QDPH D present-day instrument for this purpose, internet sites providing health information targeted at adolescents may be useful. )XWXUHVWXGLHVPD\XWLOL]HWKHSRVVLELOLWLHVRILQIRUPDWLRQWHFKQRORJ\IRUSDLQ symptom and lifestyle monitoring. Secondly, new devices have been developed 113

for activity, inactivity and sleep monitoring, and some of them may be useful even for population-based studies. Lifestyle changes in communities may bring out new variables for future studies. The current sedentary lifestyle and increasing obesity trend gives reason to consider them in future studies, even though their relationship with LBP does not seem to be very strong. The forthcoming years of follow-up of this cohort will verify whether the GHWHFWHGDVVRFLDWLRQVEHWZHHQWKHIDFWRUVHYDOXDWHGDQG/%3LQGLFDWHIXWXUHULVNV of LBP and related disability. Many health habits have yet not been established in adolescence and may be changed more easily. Individual-based health information DQGFDUHVKRXOGEHRIIHUHGWRDGROHVFHQWVVHHNLQJFDUHIRU/%3:HDOVRKRSHWKDW RXUUHVXOWVHQFRXUDJHVWDNHKROGHUVWRIRFXVRQFRPSUHKHQVLYHKHDOWKSURPRWLRQ and improvement of well-being among adolescents – not only to prevent health problems and LBP in adolescence but also later in adulthood.

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Conclusion

Persistent overweight is slightly associated with new LBP reports in the followup and it should be considered a possible determinant for LBP in future studies. 3URORQJHGKDELWXDOVPRNLQJVHHPVWREHDVVRFLDWHGZLWKUHSHDWHGUHSRUWVRI/%3 DOUHDG\ LQ DGROHVFHQFH ZKLFK HYHQ PRUH HQFRXUDJHV VPRNHIUHH DGROHVFHQFH 6RPHSK\VLFDOZRUNORDGIDFWRUVVHHPWRPRGHUDWHO\SUHGLVSRVHDGROHVFHQWVWR/%3 (VSHFLDOO\ KLJK H[SRVXUHV WR DZNZDUG WUXQN SRVWXUHV DQG DQ RYHUDOO SK\VLFDOO\ GHPDQGLQJMREFRQVWLWXWHDSUREDEOHULVNRI/%3UHSRUWV)DPLO\¶VVRFLRHFRQRPLF VWDWXVLVQRWYHU\FRQVLVWHQWO\DVVRFLDWHGZLWK/%3$GROHVFHQWVVHHPWRKDYHVRPH healthy and unhealthy behaviours concurrently, and psychosocial and lifestyle IDFWRUV IRUP FOXVWHUV &OXVWHUV FKDUDFWHUL]HG E\ EHKDYLRXUDO SUREOHPV ZHUH associated with LBP among both genders. Especially girls with a combination of HPRWLRQDODQGEHKDYLRXUDOSUREOHPVDQGSK\VLFDODFWLYLW\DUHDWWKHJUHDWHVWULVNRI VHHNLQJFDUHIRUQHZ/%3GXULQJODWHDGROHVFHQFH7KHDVVRFLDWLRQVIRXQGGLIIHUHG by gender and the need for care. The results of this study underline the multidimensional nature of LBP among DGROHVFHQWVDQGSURYLGHVRPHEDVLFLQIRUPDWLRQRQSRVVLEO\PRGL¿DEOHULVNIDFWRUV for preventive measures.

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1301. Mäkelä, Mailis (2015) Hoitoon ja kohteluun kohdistuva tyytymättömyys : potilaslain mukaiset muistutukset 1302. Nordström, Tanja (2015) Predisposing factors and consequences of adolescent ADHD and DBD : a longitudinal study in the Northern Finland Birth Cohort 1986 1303. Tanner, Tarja (2015) Healthy young adults' oral health and associated factors : cross-sectional epidemiological study 1304. Ijäs, Hilkka (2015) Gestational diabetes : metformin treatment, maternal overweight and long-term outcome 1305. Leskinen, Riitta (2015) Late-life functional capacity and health among Finnish war veterans : Veteran Project 1992 and 2004 surveys 1306. Kujala, Tiia (2015) Acute otitis media in young children : randomized controlled trials of antimicrobial treatment, prevention and quality of life 1307. Kämppi, Antti (2015) Identifying dental restorative treatment need in healthy young adults at individual and population level 1308. Myllymäki, Satu-Marja (2015) Specific roles of epithelial integrins in chemical and physical sensing of the extracellular matrix to regulate cell shape and polarity 1309. Antonoglou, Georgios (2015) Vitamin D and periodontal infection 1310. Valtokari, Maria (2015) Hoitoon pääsyn moniulotteisuus erikoissairaanhoidossa 1311. Toljamo, Päivi (2015) Dual-energy digital radiography in the assessment of bone characteristics 1312. Kallio-Pulkkinen, Soili (2015) Effect of display type and room illuminance in viewing digital dental radiography : display performance in panoramic and intraoral radiography 1313. Roivainen, Eka (2015) Validity in psychological measurement : An investigation of test norms 1314. Puhto, Ari-Pekka (2015) Prosthetic joint infections of the hip and knee : treatment and predictors of treatment outcomes 1315. Pentikäinen, Ilkka (2015) Distal chevron osteotomy for hallux valgus surgery : Role of fixation and postoperative regimens in the long-term outcomes of distal chevron osteotomy – a randomised, controlled, two-by-two factorial trial of 100 patients

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D 1316

OULU 2015

UNIVERSITY OF OUL U P.O. Box 8000 FI-90014 UNIVERSITY OF OULU FINLA ND

U N I V E R S I TAT I S

University Lecturer Santeri Palviainen

Postdoctoral research fellow Sanna Taskila

Professor Olli Vuolteenaho

Paula Mikkonen

Professor Esa Hohtola

O U L U E N S I S

ACTA

A C TA

D 1316

ACTA

U N I V E R S I T AT I S O U L U E N S I S

Paula Mikkonen

MEDICA

LOW BACK PAIN AND ASSOCIATED FACTORS IN ADOLESCENCE A COHORT STUDY

University Lecturer Veli-Matti Ulvinen

Director Sinikka Eskelinen

Professor Jari Juga

University Lecturer Anu Soikkeli

Professor Olli Vuolteenaho

Publications Editor Kirsti Nurkkala ISBN 978-952-62-0951-7 (Paperback) ISBN 978-952-62-0952-4 (PDF) ISSN 0355-3221 (Print) ISSN 1796-2234 (Online)

UNIVERSITY OF OULU GRADUATE SCHOOL; UNIVERSITY OF OULU, FACULTY OF MEDICINE; MEDICAL RESEARCH CENTER OULU; OULU UNIVERSITY HOSPITAL

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