Relationship of long working hours and night shift working hours with incident diabetes: a retrospective cohort study in Taiwan

The relationship among long working hours, night shift working hours, and diabetes is still unclear. We aimed to evaluate the association of long working hours and night shift working hours with diabetes among health care workers.We conducted a retrospective cohort study among health care workers in a tertiary medical center in Taiwan from 2002 to 2019. We compared the risk of diabetes among tertiles of total working hours (35-41, 42-45, and ≥46 h per week) and evaluated the relationship between long working hours and diabetes risk. We divided participants into three work patterns: day work only, evening shift workers, and night shift workers. In night shift workers, we further evaluated night shift working hours and incident diabetes using tertiles of night shift working hours (<17, 17-45, and ≥46 h per month). We estimated hazard ratios and 95% confidence intervals for incident diabetes using multivariable Cox proportional hazards models.The study included 7081 participants. There were 301 incident cases of diabetes during 52,454 person-years. The adjusted hazard ratio (95% confidence interval) for participants who worked greater than or equal to 46 working hours per week was 3.45 (1.27, 9.39) compared with those who worked 35-41 hours. Compared with night shift workers who worked less than 17 h, the adjusted hazard ratios (95% confidence interval) for those who worked 17-45 and ≥46 night shift working hours per month were 2.26 (1.08, 4.75) and 2.60 (1.27, 5.33), respectively.Long working hours and night shift working hours increased the risk of diabetes.