A study presented at a scientific congress yesterday reported a link between long naps and a higher risk of diabetes, though it couldn’t say if daytime sleeping was a symptom or a cause. People who slept more than an hour each day were 45% more likely to develop type 2 diabetes, the study found.
Without treatment, the disease can lead to blindness, nerve damage, kidney failure, heart disease and premature death.
The meta-analysis – a review of existing scientific literature – by Yamada Tomahide of the University of Tokyo and colleagues, covered 300 000 people of Asian and European origin from throughout the world. For naps of less than 40 minutes, the link with diabetes disappeared, they said.
Experts not involved in the research noted that the statistical correlation revealed nothing about cause-and-effect. The study, they added, has yet to be published in a peer-reviewed science journal.
“It can falsely appear that their illness followed increased napping, rather than the other way around,” said Benjamin Cairns, a researcher at the Cancer Epidemiology Unit of the University of Oxford. “This could mean that long naps appear to cause diabetes or other diseases, even when only the reverse is true.”
Naveed Sattar, an expert on metabolic disease at the University of Glasgow, said the results should be taken with a generous pinch of salt.
“It’s likely that risk factors which lead to diabetes also cause napping,” he wrote in a comment distributed by the non-profit Science Media Centre. The study was unveiled at a meeting of the European Association for the Study of Diabetes in Munich, Germany.