Objective: To investigate the association between duration of overtime and the development of impaired fasting glucose (IFG) or type 2 diabetes mellitus (DM).
Methods: A cohort of 1266 Japanese male office workers aged 35-59 years and free of IFG (fasting plasma glucose concentration 6.1-6.9 mmol/l), type 2 DM (fasting plasma glucose concentration of 7.0 mmol/l or more or taking hypoglycaemic medication), history of diabetes, or medication for hypertension were re-examined over 5 successive years after their initial examinations in 1994.
Results: 138 men developed IFG or type 2 DM during the 5736 person-years of follow up. After controlling for potential predictors of diabetes, the relative risks of IFG or type 2 DM, compared with those who worked <8.0 hours a day, were 0.82 (95% confidence interval (95% CI) 0.54 to 1.26), 0.69 (95% CI 0.38 to 1.26), 0.63 (95% CI: 0.37 to 1.09), and 0.50 (95% CI: 0.25 to 0.98) for those who worked 8.0-8.9, 9.0-9.9, 10.0-10.9, and of 11.0 hours or more a day, respectively (p for trend=0.020). 87 and 54 men developed IFG and type 2 DM during the 5817 and 5937 person-years of follow up, respectively. The multivariate adjusted relative risks of IFG tended to decrease with an increase in hours of overtime work a day, but did not reach significance (p for trend=0.202). On the other hand, the multivariate adjusted relative risks of type 2 DM significantly decreased with an increase in hours of overtime work a day (p for trend=0.014).
Conclusion: Longer overtime is a negative risk factor for the development of IFG or type 2 DM in Japanese male office workers.