Objective: Short-term partial sleep restriction results in glucose intolerance and insulin resistance. The purpose of this study was to assess the long-term relationship between sleep duration and the incidence of clinical diabetes.

Research design and methods: A cohort of men from the Massachusetts Male Aging Study without diabetes at baseline (1987-1989) were followed until 2004 for the development of diabetes. Average number of hours of sleep per night was grouped into the following categories: < or =5, 6, 7, 8, and >8 h. Incidence rates and relative risks (RRs) were calculated for the development of diabetes in each sleep duration category. Those reporting 7 h of sleep per night served as the reference group. Multivariate analysis was performed using Poisson regression.

Results: Men reporting short sleep duration (< or =5 and 6 h of sleep per night) were twice as likely to develop diabetes, and men reporting long sleep duration (>8 h of sleep per night) were more than three times as likely to develop diabetes over the period of follow-up. Elevated risks remained essentially unchanged after adjustment for age, hypertension, smoking status, self-rated health status, education, and waist circumference (RR 1.95 [95% CI 0.95-4.01] for < or =5 h and 3.12 [1.53-6.37] for >8 h). RRs were altered considerably for the two extreme sleep groups when adjusted for testosterone (1.51 [0.71-3.19] for < or =5 h and 2.81 [1.34-5.90] for >8 h), suggesting that the effects of sleep on diabetes could be mediated via changes in endogenous testosterone levels.

Conclusions: Short and long sleep durations increase the risk of developing diabetes, independent of confounding factors. Sleep duration may represent a novel risk factor for diabetes.