The effect of changes in overtime work hours on depressive symptoms among Japanese white-collar workers: A 2-year follow-up study

Objective: The purpose of this study was to investigate the effect of changes in overtime work hours on depressive symptoms among Japanese white-collar workers.

Methods: Participant data were collected from a company's annual mental health survey in June 2013 and June 2014. The participants comprised 922 workers who responded to the survey in both the years and had records of monthly working hours in the past 2 years. We obtained information on monthly working hours from personnel records from June 2012 to May 2014. Depressive symptoms were measured by the Brief Job Stress Questionnaire. Changes in overtime work hours were measured by creating a five-category variable for each monthly average of overtime work hours in the past year: (a) stable short, (b) decreased, (c) stable medium, (d) increased, and (e) stable long groups. Analysis of covariance was conducted to estimate the degree of depressive symptoms of each group for changes in overtime work hours.

Results: Significant differences among the groups were observed (F = 3.67, P = 0.006). In the Bonferroni multiple comparison test, significantly lower depressive symptoms were observed in the decreased group (point estimate = 9.56) compared to the stable short (10.76), stable medium (10.71), and increased groups (10.99). There was no significant difference between the decreased group and the stable long group (10.98).

Conclusions: A decrease in overtime work hours may prevent the deterioration of mental health. This knowledge could support the necessity of mental health measures through decreasing overtime work hours proposed by national policy in Japan.