Daytime Sleepiness, Long Naps Up Type 2 Diabetes Risk

Woman napping
Woman napping
Risk for diabetes increased by more than 40%.

Daytime sleepiness and taking long naps during the day may both be associated with an increased risk for type 2 diabetes, according to a meta-analysis presented at EASD 2015, the annual meeting of the European Association for the Study of Diabetes.

Specifically, researchers reported that excessive daytime sleepiness appeared to increase the risk for diabetes by 56%, and a daytime nap of 60 minutes or more appeared to increase this risk by 46%. 

“This research cannot prove causality. Short naps might have beneficial effects on diabetes, although we have to acknowledge the possibility of ‘reverse causality’ and the mechanisms are still unclear,” said study researcher Tomohide Yamada, MD, PhD, of the department of diabetes and metabolic diseases at the University of Tokyo in Japan.

Yamada, who presented the study findings, said results showed that a shorter nap of 60 minutes or less per day did not increase the risk for diabetes, and there was no effect of napping up to about 40 minutes per day, after which risk began to increase sharply.

Excessive daytime sleepiness is widely prevalent around the world, as is the habit of taking short sleeps or “napping.” Daytime naps are usually brief, but can range from a few minutes to a few hours. The frequency varies from taking an occasional nap to planned rest periods several times daily for habitual nappers.

Some individuals take a nap because they are excessively sleepy during the daytime as a result of a sleep disorder. Yamada said it is important to look at this issue to help identify factors such as sleep deficits and sleep apnea, which may be increasing diabetes risk.

Yamada and colleagues investigated the association between daytime sleepiness or napping and the risk for type 2 diabetes. They searched Medline, the Cochrane Library and Web of Science for articles published up to November 2014 using the keywords ‘daytime sleepiness,” “nap” and “diabetes.”

Among 683 studies initially identified, 10 studies, which involved a total of 261,365 Asian and Western subjects, were included in the analysis. The studies came from Sweden, Spain, Finland, Germany, the United States, China and Germany.

Excessive daytime sleepiness was defined as answering yes to questions like “Do you have a problem with sleepiness during the daytime?” Daytime napping was defined on the basis of answering yes to questions such as “Do you take a daytime nap?” or “Do you sleep during the day?”

Results from the pooled analysis revealed that the relative risk was 1.56 for excessive daytime sleepiness and the relative risk was 1.46 for a longer nap.

In contrast, a shorter nap of less than 60 minutes a day did not appear to increase the risk for diabetes. 

The researchers also reported that daytime napping might be a consequence of nighttime sleep disturbance such as obstructive sleep apnea. They noted that epidemiological studies have shown that obstructive sleep apnea is independently linked to ischemic heart disease, stroke, fatal and nonfatal cardiovascular events, and all-cause mortality.

“Excessive daytime sleepiness and taking longer naps could be a marker of type 2 diabetes. A short nap might have the effect of improving an abnormal circadian rhythm and modifying a variety of endocrine abnormalities caused by sleep deprivation,” Yamada told Endocrinology Advisor

“Several studies have demonstrated beneficial effects of taking short naps less than 30 minutes in duration, which help to increase alertness and motor skills. A short nap finishes before the onset of deep slow-wave sleep. 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.”

He said after analyzing the studies based on their location, study quality, and study type the researchers still found similar results. In addition, further scrutiny failed to suggest any evidence of publication bias.


  1. Yamada T et al. Abstract 940: Excessive daytime sleepiness, daytime napping, and risk of type 2 diabetes: a meta-analysis. Presented at: EASD 2015; Sept. 14-18, 2015; Stockholm.