Background: Establishing a threshold number of working hours is very important when making recommendations to protect people from the potentially harmful health effects caused by long working hours.
Aim: To clarify the influence of working hours on both mental and physical symptoms of fatigue and use the data obtained to determine permissible working hours.
Methods: Cross-sectional survey of male day-shift workers using the Self-Rating Depression Scale (SDS) and the Cumulative Fatigue Symptoms Index (CFSI). Working hours were subdivided into six groups and odds ratios were calculated for positive outcomes on the SDS and CFSI using logistic regression analysis.
Results: A total of 715 workers participated. In the group working 260-279 h/month, the odds ratios for SDS and 'irritability', 'anxiety' and 'chronic tiredness' of the CFSI were significantly increased. In the group working >or=280 h/month, the odds ratios on CFSI for 'general fatigue', 'physical disorders', 'anxiety' and 'chronic tiredness' were likewise significantly increased.
Conclusions: The present results clarified that working hours should be <260 h/month in order to minimize fatigue symptoms in male day workers.