Shift work, inflammation and musculoskeletal pain. The HUNT Study

Background: Studies have indicated that shift work, in particular night work, is associated with chronic musculoskeletal pain but the mechanisms are unclear. It has been suggested that sleep disturbance, a common complaint among shift and night workers, may induce low-grade inflammation as well as heightened pain sensitivity. Aims: Firstly, this study was aimed to examine the cross-sectional associations between shift work, C-reactive protein (CRP) level and chronic musculoskeletal pain, and secondly, to analyse CRP as a mediator between shift work and chronic musculoskeletal pain. Methods: The study included 23 223 vocationally active women and men who participated in the HUNT4 Survey of the Trøndelag Health Study (HUNT). Information was collected by questionnaires, interviews, biological samples and clinical examination. Results: Regression analyses adjusted for sex, age and education revealed significant associations between shift work and odds of any chronic musculoskeletal pain (odd ratio [OR] 1.11, 95% confidence interval [CI] 1.04-1.19), between shift work and CRP level (OR 1.09, 95% CI 1.03-1.16) and between CRP level 3.00-10 mg/L and any chronic musculoskeletal pain (OR 1.38, 95% CI 1.27-1.51). Shift work and CRP were also associated with number of chronic pain sites. Mediation analysis indicated that shift work was indirectly associated with any...