New research shows that daytime naps of over 1 hour or more increase the risk of developing type 2 diabetes by 45% compared with no napping. There is no increased risk caused by naps shorter than 60 minutes, Japanese researchers suggest.

The link is found after analysing observational studies involving more than 300,000 people. The study was carried out by scientists at the University of Tokyo and was presented at a meeting of the European Association for the Study of Diabetes in Munich.

Taking naps is widely prevalent around the world. Daytime naps are usually brief, but can range from a few minutes to a few hours.

This research found that there was a link between long daytime naps of more than 60 minutes and a 45% increased risk of type-2 diabetes, compared with no daytime napping - but there was no link with naps of less than 40 minutes.

The authors conclude that longer nap was associated with increased risk of diabetes and metabolic syndrome. Further studies are needed to confirm the efficacy of a short nap.