Naps won't make you sharper after a sleepless night, study suggests
Many people crave a mid-afternoon nap after a sleepless night.
The odd bout of insomnia will not have any lasting health consequences, but it may make you irritable, fatigued and unable to concentrate the next day.
A daytime nap may not be so restorative, however.
Scientists from Michigan State University had 280 volunteers complete a cognitive test in their sleep laboratory. Some were then allowed to go home, while the remainder were kept awake overnight.
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The next day, some of the sleep-deprived participants enjoyed a 30 minute or one hour nap, before taking a second cognitive test.
All the insomniacs performed worse than their well-rested counterparts, with the nappers faring no better than those who went without a 30 minute or one hour snooze.
"We are interested in understanding cognitive deficits associated with sleep deprivation," said study author Dr Kimberly Fenn.
"In this study, we wanted to know if a short nap during the deprivation period would mitigate these deficits.
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"We found short naps of 30 or 60 minutes did not show any measurable effects."
The cognitive tests measured the participants' attention skills and ability to complete a series of steps in a specific order, without skipping or repeating them.
"The group that stayed overnight and took short naps still suffered from the effects of sleep deprivation and made significantly more errors on the tasks than their counterparts who went home and obtained a full night of sleep," said Dr Fenn.
Nevertheless, napping may boost so-called slow-wave sleep (SWS).
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This is considered to be the deepest and most restorative stage of shut-eye, marked by high amplitude and low frequency brain waves. SWS is the sleep stage where the body is most relaxed, with slow heart and breathing rates.
"SWS is the most important stage of sleep," said Dr Fenn.
"When someone goes without sleep for a period of time, even just during the day, they build up a need for sleep. In particular, they build up a need for SWS."
The results – published in the journal Sleep – also show "every 10-minute increase in SWS reduced errors after interruptions by about 4%", according to Dr Fenn.
That percentage may sound small, however, many sleep-deprived employees are at risk of making life-threatening mistakes, like medics or lorry drivers. A 4% reduction in errors may therefore be significant, added Dr Fenn.
"Individuals who obtained more SWS tended to show reduced errors on both tasks, however, they still showed worse performance than the participants who slept," she said.
The scientists hope their results will encourage people to prioritise sleep, without relying on naps. A daytime snooze lasting more than one hour may be beneficial, however, they added.
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