Objective Epidemiological evidence on the association between night shift work and cancer risk remains limited and inconsistent. This study aimed to systematically investigate this association among Chinese men.

Methods This population-based prospective cohort study included 61 078 men from the Shanghai Men’s Health Study. Detailed information on night shift work was collected at baseline using a structured questionnaire. Cox regression model was used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for total cancer and ten major site-specific cancers. Restricted cubic spline functions were used to characterize the dose–response associations for key metrics. Further analysis was conducted with lag periods of 5, 10, 15 and 20 years, and potential effect modification by lifestyle factors was tested.

Results During a median follow-up period of 16.1 years, 8202 incident cancer cases were identified. Participants with 11–20 years of cumulative night shift work had a higher risk of pancreatic cancer compared with never-shift workers (HR 1.59, 95% CI 1.09–2.31). This association persisted across all lag periods tested, peaking at a 15-year lag (HR 1.82, 95% CI 1.25–2.64). No significant associations were found between night shift work metrics, including night shift work experience, starting age, cumulative duration, and frequency, and the risk of total and other major site-specific cancers. No evidence of effect modification by lifestyle factors was observed.

Conclusions Night shift work was not associated with the risk of overall or some common cancers among Chinese men. However, an increased risk of pancreatic cancer was associated with intermediate-to-long-term night shift work.

Key terms cancer; China; Chinese men; cohort study; epidemiology; night shift work; night work; shift worker

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