Work intervals and the prevalence of depressive symptoms among daytime workers: Japan Epidemiology Collaboration on Occupational Health Study

This study examined the association between work intervals and depressive symptoms among daytime workers, and whether lifestyle behaviors might help explain this association. A cross-sectional analysis was conducted on 8007 daytime workers who participated in a questionnaire survey of the Japan Epidemiology Collaboration on Occupational Health Study. Work intervals—both including and excluding commuting time—were calculated based on the participants' self-reported work departure and arrival times. Depressive symptoms were assessed using the 11-item Center for Epidemiological Studies Depression Scale. Multilevel robust Poisson regression models were used to estimate the prevalence ratio (PR) and 95% confidence interval (CI) for depressive symptoms across work interval categories. Five lifestyle factors (sleep duration, breakfast consumption, dietary balance, dinner timing, and leisure-time physical activity) were examined in a mediation analysis to assess the extent to which they account for the observed association. The adjusted PRs (95% CIs) for depressive symptoms were 1.41 (1.12–1.77), 1.23 (1.12–1.35), 1.03 (0.96–1.11), 1.00 (reference), and 1.08 (1.04–1.12) for those with work intervals of <11.0, 11.0–12.9, 13.0–13.9, 14.0–14.9, and ≥15.0 h, respectively. A substantial proportion of the association between shorter work intervals and depressive symptoms was explained by the lifestyle factors examined: 57.9% for <11.0 h and 57.1% for 11.0–12.9 h. Similar results were obtained when the commuting time was subtracted from the work interval. Shorter work intervals were associated with depressive symptoms, and this association may be partly related to health-related lifestyle factors. • Association between work intervals and depressive symptoms in daytime workers • Shorter work intervals were associated with a higher prevalence of depressive symptoms. • The extent to which lifestyle factors explained the association was quantitatively evaluated. • Findings support workplace regulations on daily rest time to prevent mental health problems.