Daytime sleepiness and taking long naps during the day are both associated with an increased risk of type 2 diabetes, according to a recent study.

Researchers from the University of Tokyo in Japan 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.

Sleep is an important component of a healthy life, along with a good diet and appropriate physical activity. 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.

For the study, researchers reviewed 10 studies that included more than 261,000 subjects. 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?"

They found that a shorter nap, which usually lasts 60 minutes or less, 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.

"Excessive daytime sleepiness and taking longer naps were associated with increased risk of type 2 diabetes, with a short nap not increasing this risk," authors said.

The findings were presented at this year's annual meeting of the European Association for the Study of Diabetes.