Excessive daytime sleepiness and long naps have been linked to increased risk of type 2 diabetes, revealed a new study.
For the study, the researchers did a meta-analysis to investigate the association between daytime sleepiness or napping and the risk of type 2 diabetes. The team searched Medline, the Cochrane Library, and Web of Science for articles published up to November 2014 using the keywords daytime sleepiness, nap, and diabetes.
Excessive daytime sleepiness was found to increase the risk of diabetes by 56%, while a longer daytime nap of 60 minutes or more increased the risk by 46%. In contrast, a shorter nap (60 minutes or less per day) did not increase the risk of diabetes.
The analysis suggested that there was no effect of napping up to about 40 minutes per day, after which risk began to increase sharply. The authors concluded, "Daytime napping might be a consequence of night-time sleep disturbance such as obstructive sleep apnea (OSA)."
Previous epidemiological studies have shown that OSA is independently linked to blockages (ischemia) of heart arteries, stroke, fatal and non-fatal cardiovascular events, and all-cause mortality. The researchers further added, "Entering deep slow-wave sleep and then failing to complete the normal sleep cycle can result in a phenomenon known as sleep inertia, in which a person feels groggy, disoriented, and even sleepier than before napping."
The mechanisms by which a short nap might decrease the risk of diabetes are still unclear.
The study has been presented at the annual meeting of the European Association for the Study of Diabetes (EASD).