The Relationship Between Average Daily Working Hours and Depression: A Research Based on the China Health and Retirement Longitudinal Study

Objective To investigate the relationship between average daily working hours (ADWH), working-hour trajectories, and depressive development trajectories among middle-aged and older adults in China. Methods Using observational data from 3,228 participants in the China Health and Retirement Longitudinal Study (CHARLS, 2011–2018), we employed four complementary analytical strategies—multivariate logistic regression, grouped restricted cubic spline (RCS) analysis, group-based trajectory modelling (GBTM), and multinomial logistic regression—to examine the association between ADWH, its temporal trajectories, and depression. Results Multivariate logistic regression revealed that each additional hour of daily working time increased the risk of depression by 4%–5% (OR = 1.05, P < 0.0001). RCS analysis indicated a nonlinear inflection point in the Continuous Emotional Stress Disorder-10-item scale (CESD-10) at 8 hours/day of ADWH, with no significant effect prior to 8 hours. Beyond 8 hours, each additional hour worked was associated with a 0.36-point increase in depression scores (p = 0.004). Subgroup analysis by gender revealed this relationship was more pronounced among female participants. GBTM identified four ADWH trajectories and four depression score trajectories. Multiple logistic regression of these trajectories revealed the highest risk of transitioning from the ‘persistently high work hours trajectory group’ to the ‘highest depression score trajectory group’. Subgroup analysis identified male gender, urban residence, and higher education as protective factors against depression, while frontline work and dyslipidaemia were risk factors. Conclusion Prolonged working hours increase the risk of middle-aged and older adults entering high depression trajectories, with no significant effect observed within 8 hours per day. Limiting ADWH to under 8 hours per day may serve as an effective public health strategy for preventing depression in this demographic.