Study design: A prospective cohort study.
Objective: The aim of the study was to investigate the extent to which work-related factors contribute to the social gradient in low back pain (LBP).
Summary of background data: A social gradient in LBP is well established, but only a few studies have examined the extent to which exposure to mechanical and psychosocial work environment factors is a pathway for this gradient.
Methods: A randomly drawn cohort from the general population in Norway aged 18 to 66 years was followed up for 3 years (n = 12,550, response rate at baseline = 67%). Eligible respondents were in paid work during 2006 and 2009 (n = 6819). Based on administrative register data respondents were coded into five educational levels (university/college ≥4 years was set as the reference group). Outcome of interest was self-reported moderate or severe LBP at follow-up adjusted for baseline LBP.
Results: In total, 11.2% (397 individuals) men and 14.5% (461 individual) women reported LBP at follow-up. There was a strong social gradient ranging from 16.4% (elementary) to 6.4% (university/college ≥4 years). The corresponding figures among women were 22.4% and 7.5%. Corrected for age, LBP at baseline and working hours, educational level was a significant predictor of LBP at follow-up (odds ratios 1.8-2.3 in men and 1.7-3.1 in women). Adjusting for mechanical factors reduced the gradient by 39% to 43% in men and 28% to 34% in women. Adjusting for psychosocial factors reduced the gradient by 5% to 12% in men and increased the gradient by 7% to 11% in women.
Conclusion: Work-related mechanical factors contributed substantially to the social gradient in LBP among both men and women. The impact of psychosocial factors was modest among men and contributed to an increased gradient among women.
Level of evidence: 3.