Abstract

Background
Prediabetes and diabetes represent major public health challenges, and shift work has been identified as a significant occupational risk factor. While two-shift systems are gaining preference over conventional three-shift systems, evidence comparing their risks for diabetes and prediabetes remains limited. We aimed to evaluate the risk of developing prediabetes and diabetes according to shift work patterns among night shift workers. Methods: This retrospective cohort study analyzed 14,879 night shift workers at a tertiary hospital in Korea (2016–2022). Participants were classified into two- and three-shift patterns. Incident diabetes and prediabetes were identified based on fasting blood glucose and hemoglobin A1c levels, diagnosis, or medication use. Data were censored at shift change, diagnosis, loss to follow-up, or the end of the study. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs), adjusting for demographics, lifestyle, body mass index, and occupational characteristics including working hours, consecutive night shifts, quick returns, and shift duration. Results: The two-shift group showed significantly higher incidence rates of diabetes and prediabetes than the three-shift group. After adjusting for covariates, two-shift work remained an independent risk factor for diabetes (adjusted HR: 1.43; 95% CI: 1.10–1.87) and prediabetes (adjusted HR: 1.34; 95% CI: 1.20–1.48). Stratified analyses indicated that the increased risk of diabetes associated with two-shift work was prominent in participants working 40 hours and 41–51 hours per week, whereas the association was not significant in those working ≥52 hours. Conclusions: Two-shift work was associated with a significantly higher risk of diabetes and prediabetes compared with three-shift work. Our findings highlight the need to consider specific shift schedules and their potential health effects when designing or selecting workforce systems, rather than focusing solely on productivity or preference.

• Keywords: Diabetes mellitus, Type 2; Night shift work; Occupational health; Prediabetes; Shift work schedule