Overtime Work and Prevalence of Diabetes in Japanese Employees: Japan Epidemiology Collaboration on Occupational Health Study

Objective: Epidemiologic evidence on long working hour and diabetes has been conflicting. We examined the association between overtime work and prevalence of diabetes among Japanese workers. Methods: The subjects were 40,861 employees (35,170 men and 5,691 women), aged 16 to 83 years, of 4 companies in Japan. Hours of overtime were assessed using self-reported questionnaires. Diabetes was defined as a fasting plasma glucose $126 mg/dl (7.0 mmol/l), hemoglobin A1c $6.5 % (48 mmol/mol), or current use of anti-diabetic drug. Multiple logistic regression analysis was used to calculate odds ratio of diabetes for each category of overtime. Results: After adjustment for age, sex, company, smoking, and BMI, there was a suggestion of U-shaped relationship between overtime work and prevalence of diabetes (P for quadratic trend = 0.07). Compared with those who worked,45 hours of overtime per month, the adjusted odds ratios (95 % confidence interval) of diabetes were 0.86 (0.77–0.94), 0.69 (0.53–0.89), and 1.03 (0.72–1.46) for those who worked 45–79, 80–99, and $100 hours of overtime per month, respectively. In one company (n = 33,807), where other potential confounders including shift work, job position, type of department