Overtime, psychosocial working conditions, and occurrence of non-insulin dependent diabetes mellitus in Japanese men

Objectives-To ascertain the effects of overtime and psychosocial job conditions on the occurrence of non-insulin dependent diabetes mellitus (NIDDM) in Japan. Design-An eight year prospective cohort study. Setting-An electrical company in Japan. Participants-In 1984, a mailed questionnaire was sent to industrial workers of an electrical company in Japan. After excluding those who had a history of diabetes mellitus or other chronic diseases, 2597 male respondents were prospectively followed up for the succeeding eight years. Data from 2194 (84%) who were completely followed up were analysed. The occurrence of NIDDM during the follow up period was assessed according to the WHO criteria on the basis of an annual screening programme. Main results-The age adjusted incidence of NIDDM was significantly higher in those who worked overtime more than 50 hours month than in those who worked 25 hours or less per month (p<0.05). It was significantly higher in those who worked with new technology at baseline than in those who did not (p<0.05). Cox's proportional hazard model indicated that those who worked overtime more than 50 hours per month had 3.7 times higher risk of NIDDM after controlling for known risk factors (p<0.01) and those who worked with new technology had 2.4 times higher risk of NIDDM (p<0.05). Conclusions-It is suggested that longer overtime and use of new technology are risk factors of NIDDM in Japanese men..