A nap is a short period of

sleep Sleep is a sedentary state of mind and body. It is characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity and reduced interactions with surroundings. It is distinguished from wakefulness by a de ...

, typically taken during daytime hours as an adjunct to the usual nocturnal sleep period. Naps are most often taken as a response to

drowsiness Somnolence (alternatively sleepiness or drowsiness) is a state of strong desire for sleep, or sleeping for unusually long periods (compare hypersomnia). It has distinct meanings and causes. It can refer to the usual state preceding falling asleep ...

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.

Benefits

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.

Power nap

power nap A power nap or cat nap is a short sleep that terminates before deep sleep (slow-wave sleep; SWS). A power nap is intended to quickly revitalize the sleeper. Cornell University social psychologist James Maas coined the term. A power nap combine ...

, 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 Slow-wave sleep (SWS), often referred to as deep sleep, consists of stage three of non-rapid eye movement sleep. It usually lasts between 70 and 90 minutes and takes place during the first hours of the night. Initially, SWS consisted of both St ...

, 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 Sleep debt or sleep deficit is the cumulative effect of not getting enough sleep. A large sleep debt may lead to mental or physical fatigue, and can adversely affect one's mood, energy and ability to think clearly. There are two kinds of sleep d ...

Prescribed napping for sleep disorders

It has been shown that

excessive daytime sleepiness Excessive daytime sleepiness (EDS) is characterized by persistent sleepiness and often a general lack of energy, even during the day after apparently adequate or even prolonged nighttime sleep. EDS can be considered as a broad condition encompass ...

(EDS) can be improved by prescribed napping in

narcolepsy Narcolepsy is a long-term neurological disorder that involves a decreased ability to regulate sleep–wake cycles. Symptoms often include periods of excessive daytime sleepiness and brief involuntary sleep episodes. About 70% of those affec ...

.Takashi, M. (2003). The role of prescribed napping in sleep medicine. Sleep Medicine Reviews, Vol. 7, No. 3, pp 227±235, do
10.1053/smrv.2002.0241
/ref> Apart from narcolepsy, it has not been demonstrated that naps are beneficial for EDS in other sleep disorders.

Negative effects

Sleep inertia

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 A meta-analysis is a statistical analysis that combines the results of multiple scientific studies. Meta-analyses can be performed when there are multiple scientific studies addressing the same question, with each individual study reporting me ...

showed that naps longer than an hour may be associated with an increased risk for

cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, h ...

diabetes Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ap ...

metabolic syndrome Metabolic syndrome is a clustering of at least three of the following five medical conditions: abdominal obesity, high blood pressure, high blood sugar, high serum triglycerides, and low serum high-density lipoprotein (HDL). 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

For idiopathic

hypersomnia Hypersomnia is a neurological disorder of excessive time spent sleeping or excessive sleepiness. It can have many possible causes (such as seasonal affective disorder) and can cause distress and problems with functioning. In the fifth edition ...

, patients typically experience sleep inertia and are unrefreshed after napping.Choo, K. L., Guilleminault, C. (1998). Narcolepsy and idiopathic hypersomnolence. Clin Chest Med, 19: 169±181. do
10.1016/S0272-5231(05)70440-8
/ref>

References

External links

How to nap

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. Image source dated 2008/06/14. Accessed 2009-06-16. * Text reprint �
Napping: the expert's guide

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