Heavy overtime work and depressive disorder among male workers

The association between overtime and depression is unclear and very few studies have examined the association between heavy overtime work, i.e. working more than 60 h per week, and depression.

To examine the association between heavy overtime work and the onset of depressive disorder among male workers.

A 1-year follow-up cohort study of male workers in a manufacturing company in Japan, between 2008 and 2009. Working hours, depressive disorder, assessed by the Center for Epidemiologic Studies Depression (CES-D) Scale (score ≥16 points), and covariates were measured at baseline and at follow-up. Participants who had depressive disorder at baseline were excluded.

At follow-up, 1194 participants aged between 18 and 71 years were analysed. Multiple logistic regression analysis revealed that the odds ratio for the new onset of depressive disorder was 4.5 (95% CI 1.8-11.1) times higher for employees working >60 h per week than for those working ≤50 h per week, when adjusted for age, lifestyle factors, work-related characteristics and socio-demographic characteristics at baseline and working hours at follow-up. However, the correlation between working 50.1 to 60 h per week and depressive disorder was not significant. The trend test of depressive disorder among groups by working hours was significant (P < 0.01).

Heavy overtime work is a risk factor for the new onset of depressive disorder in this population of male workers. Working >60 h per week may be the cut-off to screen for high-risk groups who need preventive action against depressive disorder.