A nap is a short period of sleep, [1] 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 or as a means to supplement before or after loss of sleep. A nap is a form of biphasic or polyphasic sleep, where the latter terms also include longer periods of sleep in addition to one period. There are multiple different types of naps depending on what the user's desired outcome may be or time constraints they may have, and 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, and naps have been shown to have various cognitive, physical, and psychosocial benefits. [2] [1]
Naps can be categorized based on their purpose and duration [3]
Napping practices can be categorized based on duration, each offering distinct benefits and considerations:
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. [16]
Research suggests that shorter, habitual naps after instruction offer the most benefits to learning. [17] [18] The benefits to alertness show no change based on duration of the nap for combating post-lunch dip, even for naps as short as 10 minutes. [19] Napping enhances alertness in young adults and adolescents during afternoons’ performances, which affect efficiency. [20] Additionally, pre-teens who nap regularly during the day demonstrate better sleep at night. In younger children, napping increased drowsiness even while improving memory recall. [21]
For students of all ages, napping during the school day showed benefits to reaction time and recall of declarative memory of new information, especially if the naps remain in slow-wave sleep, i.e. less than an hour in length. [22] [18]
In adults, a causal association has been found between habitual daytime napping and larger brain volume. [23] Brain volume normally declines with age, and is associated with neurodegenerative disease. [23] Earlier studies have shown benefits of napping for cognitive performance for healthy adults. [23]
The circadian cycle plays a role in the rising demand for daytime naps: sleepiness rises towards the mid-afternoon, hence the best timing for naps is early afternoon. [24] Twenty- to thirty-minute naps are recommended for adults, while young children and elderly people may need longer naps. [25] [26] Research, on the other hand, has shown that the benefits of napping depend on sleep onset and sleep phases rather than time and duration. [27]
It has been shown that excessive daytime sleepiness (EDS) can be improved by prescribed napping in narcolepsy. [28] Apart from narcolepsy, it has not been demonstrated that naps are beneficial for EDS in other sleep disorders. [28] For idiopathic hypersomnia, patients typically experience sleep inertia and are unrefreshed after napping. [29]
For healthy individuals in need of cognitive or emotional improvement, prescribed naps may be beneficial. [30] However, excessive napping, especially in adults with other health conditions, may be linked with negative outcomes and should be approached holistically and with caution. [30]
The state of grogginess, impaired cognition and disorientation experienced when awakening from sleep is known as sleep inertia. [31] This state reduces the speed of cognitive tasks but has no effects on the accuracy of task performance. [28] The effects of sleep inertia rarely last longer than 30 minutes in the absence of prior sleep deprivation. [32]
A 2016 meta-analysis showed that there may be a correlation between habitual napping for more than an hour, and having an increased risk for cardiovascular disease, diabetes, metabolic syndrome or death. [33] 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. No causal relationship was established: the link may be to do with people taking a longer nap in response to the pre-existence of other risk factors. [33]
Habitual naps are also an indicator of neurological degradation such as dementia in the elderly, as reduction in brain function causes more sleepiness. [34]
The need and benefits of napping vary across different age groups since sleep patterns and requirements across a person’s lifespan vary with time. [35]
How long and when a person naps affects sleep inertia and sleep latency: a person is more likely to benefit in terms of those two points when they sleep moderately in the afternoon. According to research, the degree to which a person experiences sleep inertia differs in different durations of nap. Because sleep inertia is possibly resulting from awakening from slow-wave sleep, it is more likely to happen when one has a longer nap. [41] Sleep inertia is less intense after short naps. [42] Sleep latency is shorter when a nap is taken between 3 and 5 pm, compared with a nap taken between 7 and 9 pm. [43]
According to The Sleep Foundation, Psychology Today and Harvard Health Publishing, these are the best practices for napping: [25] [44] [26]
Naps (brief sleeps) are a global and highly prevalent phenomenon
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