title: Does educational attainment increase the risk of low back pain when genetics are considered? A population-based study of Spanish twins.
abstract: There is limited research investigating educational attainment as a risk factor for low back pain (LBP), with the influence of gender commonly being neglected. Furthermore, genetics and early shared environment explain a substantial proportion of LBP cases and need to be controlled for when investigating risk factors for LBP.
  
  
  
  To investigate whether educational attainment affects the prevalence and risk of LBP differently in men and women while controlling for the influence of genetics and early shared environment.
  
  
  
  This is a cross-sectional and prospective twin case-control study.
  
  
  
  Adult monozygotic (MZ) and dizygotic (DZ) twins from the Murcia Twin Registry, with available data on educational attainment, formed the base sample for this study. The prevalence analysis considered twins with available data on LBP in 2013 (n=1,580). The longitudinal analysis considered twins free of LBP at baseline (2009-2011), with available data on LBP at follow-up (2013) (n=1,077).
  
  
  
  Data on the lifetime prevalence of activity limiting LBP (outcome) and educational attainment (risk factor) were self-reported.
  
  
  
  The prevalence analysis investigated the cross-sectional association between educational attainment and LBP, whereas the longitudinal analysis investigated whether educational attainment increased the risk of developing LBP. Both analyses were performed in the following sequence. First, a total sample analysis was performed on all twins (considering them as individuals), adjusting for confounding variables selected by the data. Second, to control for the influence of genetics and early shared environment, a within-pair case-control analysis (stratified by zygosity) was performed on complete twin pairs discordant for LBP (ie, one twin had LBP, whereas the co-twin did not). All analyses were stratified for gender where possible, with an interaction term determining whether gender was a significant moderator of the association between educational attainment and LBP.
  
  
  
  Women with either general secondary or university education were less likely to experience (prevalence analysis) or to develop LBP (longitudinal analysis). Educational attainment did not affect the risk of LBP in men. When controlling for the effects of genetics and early shared environment, the relationship between educational status and LBP in women was no longer statistically significant.
  
  
  
  Educational attainment affects LBP differently in men and women, with higher levels of education only decreasing the risk of developing LBP in women. After adjusting for genetics and early shared environment, the relationship between educational attainment and LBP in women disappears. This suggests that genetics and early shared environment are confounding the relationship between educational attainment and LBP in women.
authors.affiliation: Discipline of Physiotherapy, Faculty of Health Sciences, University of Sydney, 75 East St, Lidcombe, New South Wales, 2141, Australia. Electronic address: jzad3326@uni.sydney.edu.au.
authors.forename: Joshua R
authors.initials: JR
authors.lastname: Zadro
authors.affiliation: Discipline of Physiotherapy, Faculty of Health Sciences, University of Sydney, 75 East St, Lidcombe, New South Wales, 2141, Australia.
authors.forename: Debra
authors.initials: D
authors.lastname: Shirley
authors.affiliation: Discipline of Physiotherapy, Faculty of Health Sciences, University of Sydney, 75 East St, Lidcombe, New South Wales, 2141, Australia.
authors.forename: Marina B
authors.initials: MB
authors.lastname: Pinheiro
authors.affiliation: Department of Educational and Developmental Psychology, University of Murcia, Campus de Espinardo, 30100, Murcia, Spain; Murcia Institute for Biomedical Research, IMIB-Arrixaca, HCUVA Virgen de la Arrixaca, 30120, Murcia, Spain.
authors.forename: Juan F
authors.initials: JF
authors.lastname: Sánchez-Romera
authors.affiliation: Murcia Institute for Biomedical Research, IMIB-Arrixaca, HCUVA Virgen de la Arrixaca, 30120, Murcia, Spain; Murcia Health Council, IMIB-Arrixaca, Ronda de Levante, 11, 30008, Murcia, Spain.
authors.forename: Francisco
authors.initials: F
authors.lastname: Pérez-Riquelme
authors.affiliation: Murcia Institute for Biomedical Research, IMIB-Arrixaca, HCUVA Virgen de la Arrixaca, 30120, Murcia, Spain; Murcia Twin Registry, Department of Human Anatomy and Psychobiology, University of Murcia, Campus de Espinardo, 30100, Murcia, Spain.
authors.forename: Juan R
authors.initials: JR
authors.lastname: Ordoñana
authors.affiliation: Discipline of Physiotherapy, Faculty of Health Sciences, University of Sydney, 75 East St, Lidcombe, New South Wales, 2141, Australia.
authors.forename: Paulo H
authors.initials: PH
authors.lastname: Ferreira
mesh_terms: D000328:Adult; D000368:Aged; D004522:Educational Status; D005260:Female; D006801:Humans; D017116:Low Back Pain / Q000453:epidemiology* / Q000235:genetics; D008297:Male; D008875:Middle Aged; D012959:Socioeconomic Factors; D013030:Spain; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic
keywords: Education; Gender; Genetics; Low back pain; Murcia Twin Registry; Twin study