A poster presented at the European Association for the Study of Diabetes (EASD) meeting has reported that taking naps of an hour or longer is associated with an increased risk of type 2 diabetes.
Prof. Paul Pharoah, Professor of Cancer Epidemiology at the University of Cambridge, said:
“This study shows that in this data set long daytime naps are weakly associated with an increase in the risk of developing diabetes. Association does not imply causation.
“The study is based on a meta-analysis (pooling) of 21 different studies evaluating the association between daytime napping and diabetes risk. Each of these studies is an observational study – though it is not possible to determine the exact study design for each of them from an abstract.
“Observational studies are highly prone to bias and confounding and the weak association reported could easily be the result of this. One obvious possible bias is that people who are inactive and overweight/obese are probably more likely to take daytime naps. Such individuals are also more likely to get diabetes. Another possible explanation is reverse causation – the daytime napping is caused by undiagnosed diabetes.
“In addition meta-analyses are prone to publication bias as studies with positive associations are more likely to be published than studies with no association.”
Dr Benjamin Cairns, from the Cancer Epidemiology Unit, University of Oxford, said:
“Given the limited information that is currently available, prior to peer review and publication, its findings should be treated with caution.
“In general, it is not possible to make conclusions about cause and effect based on observational studies alone, because usually they cannot rule out alternative explanations for their findings. This applies both to primary research and to meta-analyses, like this one, which combine information from several observational studies.
“One particular difficulty in observational studies of daytime napping is that people with long-term diseases, like diabetes, often feel tired during the day due to their illness. This can even occur before they are diagnosed, so it can falsely appear that their illness followed increased napping, rather than the other way around. In research studies, this could mean that longer naps appear to cause diabetes or other diseases, even when only the reverse is true. No information has been provided on whether the individual studies contributing to this meta-analysis adequately addressed this problem, although it is likely that many of the studies would have been unable to do so.”
Prof. Naveed Sattar, Professor of Metabolic Medicine at the University of Glasgow, said:
“This observational study shows an association between longer naps and diabetes. It’s likely that risk factors which lead to diabetes also cause napping. This could include slightly high sugar levels meaning napping may be an early warning sign of diabetes.
“That said, there is now abundant evidence of a link of sorts between sleep disturbances and diabetes. What we need are trials to determine if, when and for how long one sleeps makes a difference to real health outcomes. Trials bring truth and without proper trials, we simply will never know the answer.”
‘Poster Presentation 816’ by Dr Yamada Tomahide et al. presented at the EASD meeting in Munich.