Sleep Duration and Daytime Napping and Risk of Type 2 Diabetes Among Japanese Men and Women: The Japan Collaborative Cohort Study for Evaluation of Cancer Risk.

Background: Little is known about the impacts of sleep duration and daytime napping on the risk of type 2 diabetes mellitus (T2DM).

Methods: In this study, 20,318 participants (7,597 men, 12,721 women) aged 40-79 years without a history of T2DM, stroke, coronary heart disease, or cancer at baseline (1988-1990), completed the baseline survey and the 5-year follow-up questionnaires, which included average sleep duration, napping habits, and self-reports of physician-diagnosed diabetes. The multivariable odds ratios (ORs) with 95% confidence intervals (CIs) were calculated using a logistic regression model.

Results: During the 5-year follow-up, 531 new cases of T2DM (266 men and 265 women) were documented. Sleep duration ≥10 hours was associated with higher risk of T2DM compared to sleep duration of 7 hours (OR 1.99; 95% CI, 1.28-3.08). The excess risk was observed for both sexes and primarily found among the non-overweight; the multivariable ORs of sleeping ≥10 hours compared to 7 hours were 2.05 (95% CI, 1.26-3.35) for the non-overweight (BMI <25 kg/m) and 1.38 (95% CI, 0.49-3.83) for the overweight (BMI ≥25 kg/m). The respective ORs of nappers versus non-nappers were 1.30 (95% CI, 1.03-1.63) and 0.92 (95% CI, 0.65-1.29). Among the non-overweight, nappers who slept ≥10 hours had the highest risk of T2DM (OR 2.84; 95% CI, 1.57-5.14), non-nappers who slept ≥10 hours (OR 2.27; 95% CI, 1.27-4.06), and nappers who slept <10 hours (OR 1.30; 95% CI, 1.03-1.64), compared with non-nappers who slept <10 hours.

Conclusion: Long sleep duration was associated with the risk of T2DM in both sexes, which was confined to the non-overweight.