title: Obesity does not increase the risk of chronic low back pain when genetics are considered. A prospective study of Spanish adult twins.
abstract: Obesity is commonly investigated as a potential risk factor for low back pain (LBP); however, current evidence remains unclear. Limitations in previous studies may explain the inconsistent results in the field, such as the use of a cross sectional design, limitations in the measures used to assess obesity (eg, body mass index-BMI), and poor adjustment for confounders (eg, genetics and physical activity).
  
  
  
  To better understand the effects of obesity on LBP, our aim was to investigate in a prospective cohort whether obesity-related measures increase the risk of chronic LBP outcomes using a longitudinal design. We assessed obesity through measures that consider the magnitude as well as the distribution of body fat mass. A within-pair twin case-control analysis was used to control for the possible effects of genetic and early shared environmental factors on the obesity-LBP relationship.
  
  
  
  Data were obtained from the Murcia Twin Registry in Spain. Participants were 1,098 twins, aged 43 to 71 years, who did not report chronic LBP at baseline. Follow-up data on chronic LBP (>6 months), activity-limiting LBP, and care-seeking for LBP were collected after 2 to 4 years.
  
  
  
  The risk factors were BMI, percentage of fat mass, waist circumference, and waist-to-hip ratio.
  
  
  
  Sequential analyses were performed using logistic regression controlling for familial confounding: (1) total sample analysis (twins analyzed as independent individuals); (2) within-pair twin case-control analyses (all complete twin pairs discordant for LBP at follow-up); and within-pair twin case-control analyses separated for (3) dizygotic and (4) monozygotic twins.
  
  
  
  No increase in the risk of chronic LBP was found for any of the obesity-related measures: BMI (men/women, odds ratio [OR]: 0.99; 95 % confidence interval [CI]: 0.86-1.14), % fat mass (women, OR: 0.87; 95% CI: 0.66-1.14), waist circumference (women, OR: 0.98; 95% CI: 0.74-1.30), and waist-to-hip ratio (women, OR: 1.05; 95% CI: 0.81-1.36). Similar results were found for activity-limiting LBP and care-seeking due to LBP. After the adjustment for genetics and early environmental factors shared by twins, the non-significant results remained unchanged.
  
  
  
  After 2 to 4 years, obesity-related measures did not increase the risk of developing chronic LBP or care-seeking for LBP with or without adjustment for familial factors such as genetics in Spanish adults.
authors.affiliation: Discipline of Physiotherapy, Faculty of Health Sciences, University of Sydney, PO Box 170, Lidcombe, Sydney 1825, Australia. Electronic address: adar3900@sydney.edu.au.
authors.forename: Amabile Borges
authors.initials: AB
authors.lastname: Dario
authors.affiliation: The George Institute for Global Health, Sydney Medical School, University of Sydney, PO Box M201, Missenden Rd, NSW 2050, Australia; Institute of Bone and Joint Research, The Kolling Institute, Sydney Medical School, University of Sydney, Reserve Road, St Leonards, NSW 2605, Australia.
authors.forename: Manuela
authors.initials: M
authors.lastname: Loureiro Ferreira
authors.affiliation: Discipline of Physiotherapy, Faculty of Health Sciences, University of Sydney, PO Box 170, Lidcombe, Sydney 1825, Australia.
authors.forename: Kathryn
authors.initials: K
authors.lastname: Refshauge
authors.affiliation: Discipline of Physiotherapy, University of Málaga, Avenida Cervantes, 2, 29071 Malaga, Spain.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Luque-Suarez
authors.affiliation: Murcia Twin Registry, Department of Human Anatomy and Psychobiology, University of Murcia, Campus de Espinardo, 30100 Murcia, Spain; IMIB-Arrixaca, HUVA Virgen de la Arrixaca, 30120 Murcia, Spain.
authors.forename: Juan Ramon
authors.initials: JR
authors.lastname: Ordoñana
authors.affiliation: Discipline of Physiotherapy, Faculty of Health Sciences, University of Sydney, PO Box 170, Lidcombe, Sydney 1825, Australia.
authors.forename: Paulo Henrique
authors.initials: PH
authors.lastname: Ferreira
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D017116:Low Back Pain / Q000453:epidemiology* / Q000235:genetics; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology* / Q000235:genetics; D011446:Prospective Studies; D013030:Spain; D014430:Twins, Monozygotic
keywords: Anthropometric measures; Body mass index; Case-control; Genetics; Low back pain; Obesity; Twin