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Napping May Be Linked with Type-2 Diabetes

Naps of 60 minutes per day or longer were associated with an increased risk of 50% for risk of type 2 diabetes.

Getting enough sleep is widely accepted as a component of good health. A lack of sleep is associated with cardiovascular disease, weight gain, memory problems, injuries, and learning impairment, among other negative effects. Too much sleep during the day may be harmful as well, however. A new meta-analysis presented at the European Association for the Study of Diabetes (EASD) 2015 annual meeting suggests a link between excessive sleepiness and type-2 diabetes risk.

The meta-analysis was conducted by a team of researchers from the University of Tokyo in Japan. Databases searched included Medline, Cochrane Library, and Web of Science. The authors only included articles published up to November of 2014. The keywords used include daytime sleepiness, nap, and diabetes. The authors analyzed the validity of the studies they looked at with two methods. First, they referred to the STROBE Statement for observational studies. They also referenced the Newcastle-Ottawa Scale for observational studies in meta-analyses. The authors controlled for publication bias with funnel plot, Egger’s test, and Begg’s test, all of which did not reveal publication bias.

Initially the meta-analysis identified 683 studies with a total of 261,365 subjects (both Western and Asian). The analyses of the studies were confounded for diabetes confounders like BMI. Overall, excessive daytime sleepiness and naps of 60 minutes per day or longer were associated with an increased risk of 50% for risk of type 2 diabetes. Relative risk for excessive sleepiness was 1.56 (95% CI 1.13-2.14, p=0.006) while relative risk for a longer nap was 1.46 (95% CI 1.23-1.74, p<0.001). Naps that were less than 60 minutes per day did not have a significant correlation with risk of diabetes. Analysis with cubic spline model for a dose-response meta-analysis revealed that napping for up to 40 minutes per day had no effect on diabetes risk, while risk for diabetes increased directly with longer nap times.

More evidence is necessary to further analyze the relationship between excessive daytime sleepiness, longer nap times, and the risk of type-2 diabetes mellitus. It is unclear whether the sleepiness itself, some other factor causing the sleepiness, or effects associated with sleepiness result in the increased risk.

Practice Pearls:

  • Excessive daytime sleepiness along and naps of 60 minutes per day or longer are associated with increased risk of type-2 diabetes according to a new meta-analysis.
  • The meta-analysis examined observational studies including 261,365 patients. The patients were both Western and Asian.
  • Although the correlation between sleepiness and diabetes was found to be statistically significant, the exact causal relationship remains unclear.

Yamada T, Shojima N, Hara K, et al. Excessive daytime sleepiness, daytime napping, and risk of type 2 diabetes: a meta-analysis. Abstract #940. Presented at the 49th Annual Meeting of the European Association for the Study of Diabetes. 2015.