Should nappers be concerned? Japanese researchers say that napping for more than an hour is associated with developing type 2 diabetes.
But it鈥檚 probably not the nap itself that鈥檚 to blame, instead daytime sleeping is most likely a symptom of grossly disturbed or otherwise inadequate rest at night.
The research, presented at of the , found no link between nap time and increased obesity risk. However, my hunch is that existing obesity rather than the naps themselves is what鈥檚 raising diabetes risk.
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We know obesity makes diabetes more likely and also raises the risk of . This apnoea produces heavy snoring and gagging due to total or partial collapse of the upper airway 鈥� the 鈥渙ropharynx鈥�, which naturally relaxes during sleep, but is compressed further by the weight of fat around the neck.
A 鈥減ot belly鈥� which makes breathing even harder during sleep is also often linked to a raised risk of diabetes. I suspect that taking long naps 鈥� a sign of excessive daytime sleepiness 鈥� is only indirectly linked to diabetes.
Sleep and weight gain
This new napping analysis is just the latest in a long line of speculation about sleep鈥檚 impact on health. For example, there have been many other findings of seemingly statistically significant correlations between a , implying that longer sleep will prevent weight gain.
But weight gains that might be attributed to short sleep are small, even for 5-hour sleepers, who put on less than 2 kilograms over a year on average. This contrasts with hundreds of hours of 鈥渓ost鈥� sleep when compared with 7-hour sleepers.
Besides, few obese adults sleep so little, and even if that small weight gain was prevented by more sleep, with the far more rapid results of a better diet and just half an hour of daily exercise.
There are also short-term studies where in healthy lean young adults, for several nights, and they find diabetes-like changes (quickly reversed with recovery sleep).
Although these findings seem to back up some of the claims, this is too extreme a degree of sleep restriction, which is stressful and clearly unrealistic, especially given the debilitating daytime sleepiness that results.
Power naps
So is there any general, robust advice on napping time? Occasional short 鈥減ower naps鈥� can be very refreshing but keep them to 20 minutes otherwise full-blown sleep gets under way, confusing the 24 hour circadian body clock.
The resultant grogginess on waking is a form of jet lag that can last for hours and disrupt that night鈥檚 sleep.
Take a tip and have some caffeine immediately before such a nap (not afterwards) as the caffeine takes about 20 minutes to kick in, creating an ideal window of opportunity for the nap. This combined effect of both caffeine and nap can be very effective.
By the way, you can take a regular longer siesta every afternoon without disrupting that night鈥檚 sleep. This is because it becomes part of your body clock and doesn鈥檛 cause jet lag.
Jim Horne is former head of the at Loughborough University, UK, and author of (Palgrave Macmillan)
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