We performed a case-control and a cohort study. Subjects were office workers in four Japanese companies. Diagnosis of depression was made by two psychiatrists who conducted independent clinical interviews using DSM-IV-TR criteria.
There was no significant association between working overtime and the onset of depression. The frequency of alcohol intake was significantly related to the onset of depression. We also found a significant relation between younger age and depression onset. Body mass index and physical illness, including diabetes mellitus, had no significant association with depression onset.
Data were self-reported and the number of included female workers was small.
Reducing working hours alone is unlikely to be effective in preventing workers' depression. Additional countermeasures are needed, including a reduction in alcohol intake and work stress. Considerations for younger workers are also needed.