London: While taking a short nap may be good for your health, extending it to an hour or more significantly increases risk of developing diabetes, says a new study.

“Excessive daytime sleepiness and taking longer naps were associated with increased risk of Type-2 diabetes, with a short nap not increasing this risk,” the study said.

The research by Tomohide Yamada from University of Tokyo in Japan analysed studies published till November 2014 on the association between daytime sleepiness, nap, and diabetes.

After examining over 600 hundred studies including 261,365 people from Asian and Western countries, the research found that excessive daytime sleepiness increased the risk of diabetes by 56 percent, while a longer daytime nap of 60 minutes or more increased the risk by 46 percent.

In contrast, a shorter nap (60 mins or less per day) did not increase the risk of diabetes.

The analysis showed there was no effect of napping up to about 40 minutes per day, after which risk began to increase sharply.

“Daytime napping might be a consequence of night-time sleep disturbance such as obstructive sleep aponea (OSA),” the study noted.

Several studies have demonstrated the 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,” Yamada said.

“Although the mechanisms by which a short nap might decrease the risk of diabetes are still unclear, such duration-dependent differences in the effects of sleep might partly explain our findings,” Yamada noted.

The findings were presented at the annual meeting of the European Association for the Study of Diabetes (EASD) in Stockholm, Sweden.