A nap is a short period of sleep, typically taken during daytime hours as an adjunct to the usual nocturnal sleep period. Naps are most often taken as a response to drowsiness during waking hours. A nap is a form of biphasic or polyphasic sleep, where the latter terms also include longer periods of sleep in addition to one single period.
For years, scientists have been investigating the benefits of napping, including the 30-minute nap as well as sleep durations of 1–2 hours. Performance across a wide range of cognitive processes has been tested.
Sara Mednick conducted a study experimenting on the effects of napping, caffeine, and a placebo. Her results showed that a 60–90-minute nap is more effective than caffeine in memory and cognition.
A power nap, also known as a Stage 2 nap, is a short slumber of 20 minutes or less which terminates before the occurrence of deep slow-wave sleep, intended to quickly revitalize the napper. The power nap is meant to maximize the benefits of sleep versus time. It is used to supplement normal sleep, especially when a sleeper has accumulated a sleep deficit.
Prescribed napping for sleep disorders
It has been shown that excessive daytime sleepiness (EDS) can be improved by prescribed napping in narcolepsy. Apart from narcolepsy, it has not been demonstrated that naps are beneficial for EDS in other sleep disorders.
The state of grogginess, impaired cognition and disorientation experienced when awakening from sleep is known as sleep inertia. This state reduces the speed of cognitive tasks but has no effects on the accuracy of task performance. The effects of sleep inertia rarely last longer than 30 minutes in the absence of prior sleep deprivation.
Potential health risks
A 2016 meta-analysis showed that naps longer than an hour may be associated with an increased risk for cardiovascular disease, diabetes, metabolic syndrome or death. There was no effect of napping for as long as 40 minutes per day, but a sharp increase in risk of disease occurred at longer nap times.
On sleep disorders
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- Yamada, Tomohide; Shojima, Nobuhiro; Yamauchi, Toshimasa; Kadowaki, Takashi (2 December 2016). "J-curve relation between daytime nap duration and type 2 diabetes or metabolic syndrome: A dose-response meta-analysis". Scientific Reports. 6 (1): srep38075. doi:10.1038/srep38075. ISSN 2045-2322. PMC 5133463. PMID 27909305.
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