London - Grabbing 40 winks in the afternoon can increase the risk of heart disease and diabetes, a study has found.
It suggests daytime sleepiness may be a warning of metabolic syndrome - the medical term for a combination of diabetes, high blood pressure and obesity.
Specifically, having a nap of 40 minutes or more was associated with a steep increase in the danger - up to 50 per cent for those who spent 90 minutes asleep. Being overtired during the day also raised the risk by the same amount, according to the research.
Up to 15 million in the UK are thought to suffer from metabolic syndrome and to be at greater risk of developing heart disease or suffering from a stroke.
More are developing the risky combination of symptoms across the world and scientists are desperate to prevent new cases.
The study — one of the largest of its kind – took data from 21 other studies involving more than 307,000 participants of both Asian and Western ethnicities.
It focused on the link between lengthy naps and daytime sleepiness with heart disease and type 2 diabetes.
Participants were asked whether they felt sleepy during the day and whether they took daytime naps. Their answers where then analysed alongside their history of type 2 diabetes and obesity.
The results revealed those who napped for less than 40 minutes had no increased risk of developing metabolic syndrome.
But the risk sharply increased once participants dropped off for longer than 40 minutes.
And a lengthy 90 minute nap increased the risk of developing the syndrome by 50 per cent, along with being excessively tired during the day. Those who napped for less than 30 minutes a day appeared to slightly decrease their risk of developing the syndrome.
It is not the first time the potential health risks of napping have been raised.
In an earlier study by the same researchers, published in the journal Sleep, naps that lasted for longer than an hour were tied to an 82 per cent increase of cardiovascular disease and a 27 per cent increase in all causes of death. Another piece of research, presented at the Annual Meeting of the European Association for the Study of Diabetes last year, showed that naps lasting longer than an hour increased the risk of diabetes by 46 per cent.
The team behind the new research, due to be presented at the American College of Cardiology’s Annual Scientific Session, stressed the importance of studying sleep patterns.
Study author Dr Tomohide Yamada, from the University of Tokyo, said: ‘Taking naps is widely prevalent around the world.
‘So, clarifying the relationship between naps and metabolic disease might offer a new strategy of treatment, especially as metabolic disease has been increasing steadily all over the world.
‘Sleep is an important component of our healthy lifestyle, as well as diet and exercise. Short naps might have a beneficial effect on our health, but we don’t yet know the strength of that effect or the mechanism by which it works.’
Daily Mail