Napping for more than an hour during the day could be a warning sign for type-2 diabetes, Japanese researchers suggest. They found the link after analysing observational studies involving more than 300,000 people. UK experts said people with long-term illnesses and undiagnosed diabetes often felt tired during the day. But they said there was no evidence that napping caused or increased the risk of diabetes. The large study, carried out by scientists at the University of Tokyo, is being presented at a meeting of the European Association for the Study of Diabetes in Munich. Their research found 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.