In 2009 a UK National Siesta Day was cancelled due to reports of research showing that napping causes diabetes. Was this an unfortunate knee-jerk reaction to really bad media reporting, blurring the distinction between cause and association? Or is, in fact, the humble nap a dangerous practice when it comes to our health?
NapNow sought the views of a nap scientist to help put the record straight. Dr Nicole Lovato, School of Psychology, Flinders University, has studied napping for eight years herself, and knows the research well. “I became interested in this area after finding I was spending a lot of time napping after having Glandular Fever in my undergraduate years,” says Lovato. “I would feel overwhelming sleepiness and found after a short nap, I felt much more alert and refreshed.”
NapNow: Some research has reported associations between napping and increased risk of several medical problems, including Type 2 Diabetes and high cholesterol. What can we conclude from these?
The majority of these studies are cross-sectional in nature, so they are not designed to establish whether napping can cause medical problems. Experimental and prospective studies are needed to assess the casual direction between medical issues and napping, i.e. – is napping causing the health problem or is the health problem causing napping?
Many individuals with co-existing medical and sleep problems, such as diabetes and sleep apnoea, also experience excessive levels of daytime sleepiness. It is likely underlying medical issues are contributing to daytime sleepiness, which is in turn relieved by napping. For example, diabetes itself induces tiredness, which may encourage napping.
Interestingly the association between napping and a medical condition is typically found with the longer naps of greater than 30 minutes.
NapNow: Are there any downsides of napping that are well established?
Lovato: After a long nap of about one to two hours, you can feel worse before you feel better. In the transition from sleep to wake, many people report feeling groggy. This groggy feeling is called sleep inertia and it leaves people feeling flat, sleepy and slow in body and mind for up to 30 minutes, after emerging from a nap. Longer naps could therefore be ‘dangerous’ if you started driving, operating machinery, or making critical decisions immediately after waking.
The magnitude of sleep inertia depends on several factors, the most important being the amount of slow wave sleep (deep sleep) gained within the nap. Given slow wave sleep develops gradually over time, long naps typically produce longer and more intense periods of sleep inertia upon awakening.
Long daytime naps with a substantial amount of slow wave sleep will make it difficult to fall asleep that night.
Brief naps that contain about five to 10 minutes of sleep are associated with short periods of sleep inertia or none at all.
So if you want to protect your nighttime sleep and avoid feeling groggy, keep the nap short and early in the afternoon.
NapNow: We hear a lot about all the good things napping can do for us – are these claims based on good science?
Lovato: The alerting benefits of naps are well established. A brief power nap can reduce sleepiness, improve cognitive functioning such as problem solving and decision making, and psychomotor performance including reaction time. It also enhances short-term memory and mood. These benefits are similar to those experienced after consuming caffeine and other stimulant medications, but without the side effects of dependence on caffeine or the possibility of interfering with nighttime sleep.
NapNow’s take home:
- Generally speaking, keep your regular naps short and you can enjoy all the benefits without the downsides. This equates to lying down for no more than 20 to 30 minutes, to allow for 10 to 20 minutes of actual sleep.
- If you’re feeling really sleep deprived and want a long nap, allow up to half an hour afterwards before expecting too much from yourself.
- If you constantly experience daytime sleepiness, or feel the need to regularly nap for an hour or more despite sufficient nighttime sleep, see a doctor. A medical problem may be causing or contributing to your lack of daytime alertness.
SIDE BAR: When it comes to napping, Timing is Everything.
“Naps from 5 minutes to 2 hours can increase alertness, but the way these benefits emerge after waking varies according to the length of the nap,” says Lovato.
The 10 to 20 minute nap offers an almost immediate pick-me-up effect.
The benefits can last up to three hours. [Sound ideal to get you through the afternoon slump?]
The longer, 1 to 2 hour nap offers a delayed, but longer lasting effect. You’ll probably have to wait anywhere from 10 to 30 minutes before you start feeling refreshed after waking. The benefits of these longer naps typically last longer, even up to 24 hours after waking.
Her research interests include sleep, circadian rhythms, and insomnia. She is particularly interested in how the disturbance of sleep can impact on daytime functioning and mood. Her research is aimed at understanding this relationship and evaluating the use of different treatment strategies, such as cognitive-behaviour therapy, bright light, melatonin administration and napping, to minimise the adverse effects of poor sleep.