Shift work and the risk of knee osteoarthritis among Chinese workers: a retrospective cohort study.

Objectives Shift work is associated with metabolic disorders as it disturbs circadian rhythms. However, the potential association of shift work with knee osteoarthritis (KOA), a metabolic-related disease, has not been confirmed. The objective of this study was to quantify the association of shift work with the risk of KOA. Methods This retrospective cohort study comprising 13 741 retired workers from the Dongfeng Motor Corporation. KOA was defined by knee pain and clinical X-ray radiographs. Occupational history, including job description and shift work, was collected from face-to-face interviews using questionnaires. Cox proportional hazards regression models were used to estimate exposure-response relationships. Results During the 590 085 person-years of follow-up, a total of 847 cases of KOA (incidence of KOA was 143.5 per 100 000 person-years) were identified. After adjusting for potential confounders, shift work was independently associated with an elevated risk of KOA [hazard ratio (HR) 1.19, 95% confidence interval 1.03-1.36]. Compared with daytime workers, the risk of KOA increased with prolonged periods of shift work; the HR of KOA for participants with 1-9 years, 10-19 years, and ≥20 years shift work were 1.03 (95% CI 0.84-1.26), 1.19 (95% CI 0.98-1.46), and 1.42 (95% CI 1.15-1.76), respectively. The HR for KOA associated with shift work gradually decreased as the period after finishing shift work increased. Conclusion Our results indicated that shift work could be an independent risk factor for KOA.