Effects of overtime work on blood pressure and body mass index in Japanese male workers

Background Effects of overtime work on health is a controversial issue. Aims To determine the effects of overtime work on blood pressure and body mass index (BMI) for male workers in Japan. Methods Participants were 323 male participants of three companies. Data were collected by occupational physicians at periodic physical examinations and additional examinations. The time courses for the development of definite hypertension and an increase in BMI were recorded. The Kaplan-Meier method was used to estimate the cumulative incidence rates of developing definite hypertension and increasing BMI, and the Cox proportional hazard model was used to determine the adjusted relative hazard of overtime work. Results The age-adjusted incidence rates of developing definite hypertension and increasing BMI were significantly lower among the participants whose mean overtime was >= 50 h than among those whose mean overtime was < 50 h/month (log-rank P < 0.05). The Cox proportional hazard model indicated that those who worked a mean overtime of >= 50 h/month had lower risks of developing definite hypertension (hazard ratio, 0.36; 95% CI, 0.15-0.88; P < 0.05) and increasing their BMI (hazard ratio, 0.44; 95% CI, 0.31-0.63; P < 0.01) after adjusting for age. Conclusions The results of this study indicate that workers whose mean overtime was >= 50 h have lower risks of developing definite hypertension and increasing their BMI.