Occupational Medicine Advance Access published online on November 10, 2008
Occupational Medicine, doi:10.1093/occmed/kqn141
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Overtime work and stress response in a group of Japanese workers
1 Department of Occupational Health, Faculty of Medicine, McGill University, Montreal, Quebec, Canada
2 Central Health Support and Promotion Division, Fujitsu Limited, Kawasaki, Kanagawa, Japan
Background Working long overtime hours is considered a cause of mental health problems among workers but such a relationship has yet to be empirically confirmed.
Aim To clarify the influence of overtime work on response to stress and to assess the role of other stress-related factors on this relationship.
Methods The study was conducted among 24 685 employees of a company in Japan. Stress response, job stressors and social supports were assessed by the Brief Job Stress Questionnaire. Participants were divided into five categories of overtime (0–19, 20–39, 40–59, 
60 h of overtime per month and exempted employees).
Results The nonadjusted odds ratios for stress response for 40–59 and 60 overtime hours per month in reference to 0–19 overtime hours were 1.11 [95% confidence interval (CI) 1.03–1.19] and 1.62 (95% CI 1.50–1.76), respectively. After adjustment for self-assessed amount of work, mental workload and sleeping time, the association between overtime work and stress response disappeared.
Conclusions This large cross-sectional study shows that overtime work appears to influence stress response indirectly through other stress factors such as self-assessed amount of work, mental workload and sleeping time.
Keywords Long working hours; mental health; occupational health; psychological stress
Correspondence to: Gilles Thériault, Department of Occupational health, Faculty of Medicine, McGill University, 1020 Pine Avenue West, Montreal, Quebec H3A1A2, Canada. Tel: +1 514 398 5110; fax: +1 514 398 7435; e-mail: gilles.theriault{at}mcgill.ca