Sleep debt and depressive symptoms among workers: the mediating role of fatigue

Introduction This study examined whether fatigue mediates the association between sleep debt and depressive symptoms among municipal employees in Japan. Methods This cross-sectional study was conducted as part of the Night in Japan Home Sleep Monitoring Study (NinJaSleep Study) between November 2023 and March 2024 among 1,435 municipal employees in Koka City, Japan. Sleep debt was quantified using the Sleep Debt Index, calculated from self-reported ideal and actual sleep duration. Depressive symptoms were assessed using the Patient Health Questionnaire-9 (PHQ-9), and fatigue was assessed using the Chalder Fatigue Scale. Mediation analysis was performed using the PROCESS macro (Model 4), adjusting for age, sex, body mass index, and occupation. Indirect effects were estimated using bootstrapping with 5,000 resamples. Results Sleep debt was significantly associated with higher fatigue scores ( B = 2.37, p < 0.001), and fatigue was positively associated with depressive symptoms ( B = 0.32, p < 0.001). The direct association between sleep debt and depressive symptoms was not statistically significant ( B = 0.07, p = 0.36). Mediation analysis indicated that the association between sleep debt and depressive symptoms was significantly mediated by fatigue (indirect effect: B = 0.76, 95% CI: 0.61–0.91). Discussion Sleep debt is associated with depressive symptoms primarily through increased fatigue. These findings highlight fatigue as a key pathway in linking insufficient sleep to mental health outcomes and underscore the importance of addressing fatigue in workplace mental health strategies.