Greater social jetlag and late chronotypes have been linked to poor glucose metabolism, but their effects on diabetes risk in Asians remain unclear. This study investigated the prospective association between social jetlag, chronotype and diabetes risk among Japanese workers. We included 1681 workers (73% were daytime workers) aged 18-78 years who attended a nutritional survey in 2015 and 2016 and were followed for diabetes incidence until May 31, 2022. Social jetlag was defined as the absolute difference in the midpoint of sleep times between weekdays and weekends. Chronotype was estimated using the mid-sleep time on weekends that was corrected with sleep debt on weekdays. Following the American Diabetes Association criteria, diabetes onset was defined as the time when the participant first met any of the following conditions: HbA1c ≥ 6.5%, fasting plasma glucose ≥ 126 mg/dL, random plasma glucose ≥ 200 mg/dL or current use of antidiabetic medication. The Cox proportional hazards model was used to estimate hazard ratios (HRs) for diabetes incidence. Among the study participants, 88.8% were male, 5.0% experienced ≥ 2 h of social jetlag, and 7.6% were classified as having a late chronotype. During the 7-year follow-up, 107 individuals (6.4%) developed diabetes. Among daytime workers, social jetlag was not associated with diabetes risk: multivariable-adjusted HRs (95% CI) for diabetes were 1.00, 0.90 (0.52-1.55) and 1.08 (0.43-2.75) in participants with < 1.0, 1.0 to 1.9, and ≥ 2.0 h of social jetlag, respectively. Late chronotype was associated with higher diabetes risk, although not statistically significant, compared to early chronotype; multivariable-adjusted HRs (95% CI) were 1.32 (0.80-2.18) for intermediate chronotype and 1.98 (0.77-5.10) for late chronotype. In conclusion, this study suggests an association between late chronotypes and increased risk of diabetes among daytime workers and also highlights a mediating role of lifestyle-related behaviours on chronotype and their impact on metabolic health.
