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, >or=60 h of overtime per month and exempted employees). RESULTS: The nonadjusted odds ratios for stress response for 40-59 and >or=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.
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, >or=60 h of overtime per month and exempted employees). RESULTS: The nonadjusted odds ratios for stress response for 40-59 and >or=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.