Naps

Studies usually classify naps by frequency, from occasional to daily, and by length, most often using one hour as the dividing line between shorter and longer naps [2, 5]. Most studies rely on a single self-reported answer about how often and how long a person naps. A 2017 National Sleep Foundation panel could not agree on whether napping should be counted as an indicator of good or poor sleep quality [7].

Napping changes with age. In 1,401 older adults of the Rush Memory and Aging Project whose daytime sleep was measured with wrist-worn activity monitors for up to 14 years, naps became longer and more frequent each year. Among participants who developed Alzheimer's dementia, the yearly increase in nap duration and frequency more than doubled [1].

A 2024 pooled analysis combined 21 studies with 371,306 participants. Compared with people who did not nap, those who napped had 28% higher all-cause mortality (hazard ratio 1.28, 95% CI 1.18 to 1.38, where 1.00 means no difference). Divided by length, naps of less than an hour showed no association (1.00, 0.90 to 1.11), while naps of an hour or more were associated with 22% higher mortality (1.22, 1.12 to 1.33) and 37% higher risk of cardiovascular disease (1.37, 1.09 to 1.71) [2].

An earlier pooled analysis of 11 prospective studies with 151,588 participants, a mean follow-up of 11 years and 18,966 deaths found the same division. Daily naps of 60 minutes or more were associated with 27% higher all-cause mortality and 82% higher cardiovascular disease risk than no napping, while naps under 60 minutes were not significantly associated with either outcome. When nap length was modelled continuously, all-cause mortality rose in a straight line by about 4% for every additional 10 minutes of napping per day [5].

The relationship between nap length and cardiovascular disease is not a straight line. In the 2015 pooled analysis, cardiovascular risk fell slightly from no napping to about 30 minutes a day, rose slightly up to about 45 minutes, and then increased sharply with longer naps, a J-shaped curve [5].

Some individual studies have found lower risk with napping. Among 23,681 Greek adults free of heart disease, stroke and cancer at the start and followed for a mean of 6.3 years, those who took a siesta of any frequency or length had 34% lower coronary mortality than those who did not, and those who napped regularly had 37% lower coronary mortality; the association was strongest in working men [6]. In 3,462 Swiss adults followed for 5.3 years, people who napped once or twice a week had about half the risk of a cardiovascular event of non-nappers (hazard ratio 0.52, 95% CI 0.28 to 0.95). Daily napping was associated with higher risk before adjustment for other risk factors but not after, and nap length showed no association [8]. Both studies had relatively few cardiovascular deaths or events, and the Swiss findings suggest that nap frequency, not only length, may explain differences between studies.

Laboratory studies measure the effect of a nap on alertness and performance over the following hours. In a pooled analysis of 11 studies with 381 working-age participants, mostly under laboratory conditions, cognitive performance improved after a nap compared with no nap (effect size 0.18), especially alertness (0.29, 95% CI 0.10 to 0.48). The average nap lasted 55 minutes, performance improved for up to 120 minutes afterwards, and neither nap length nor sex or age changed the size of the benefit. Naps taken before 1 p.m. were associated with better performance, although that estimate was imprecise [3].

Very short naps have been compared directly. In 24 healthy young adults whose night-time sleep had been restricted to about 5 hours, a 5-minute nap at 3 p.m. produced few benefits. A 10-minute nap produced immediate improvements in sleepiness, fatigue, vigour and cognitive performance, some lasting up to 155 minutes. After a 20-minute nap, improvements appeared 35 minutes later and lasted up to 125 minutes. A 30-minute nap was followed by a period of impaired alertness and performance before improvements appeared [4]. This temporary grogginess after waking is called sleep inertia; in this study it followed the 30-minute nap but not the shorter ones [4]. Sleep stages are described in sleep physiology.

A 2023 UK Biobank study used Mendelian randomisation, a method that uses genetic variants as a natural experiment to estimate cause and effect, to examine napping and the brain. With 92 genetic variants linked to habitual daytime napping in up to 378,932 people, a genetic tendency to nap was associated with a larger total brain volume (15.8 cm³, 95% CI 0.25 to 31.34), but not with hippocampal volume, reaction time or visual memory. The authors described the association as modest and called for replication [9]. The study measured genetic tendency to nap rather than actual napping, and it did not measure mortality, cognitive decline or dementia.

Observational data in older adults point the other way for excessive napping. In the Rush Memory and Aging Project, longer and more frequent daytime naps measured by wrist monitors were associated with a higher risk of Alzheimer's dementia. Excessive napping was associated with worse cognition a year later, and worse cognition with more excessive napping a year later, which the authors interpreted as a possible two-way relationship or shared underlying disease process [1]. Related evidence is covered in cognitive aging and dementia risk factors.

Most napping studies record napping once, by self-report, and cannot distinguish a planned short nap from unintended dozing caused by illness or sleepiness. Both large pooled analyses were based on observational studies, so reverse causation (illness causing long naps rather than the reverse) is possible: poor night-time sleep, obstructive sleep apnea, depression, heart failure and early neurodegenerative disease all increase daytime sleep and independently shorten life [2, 5]. The links between night-time sleep, sleep disorders and lifespan are covered in sleep duration and mortality.

The alertness evidence comes from small laboratory studies measuring outcomes over hours, not years, and mostly in young, healthy adults [3, 4]. No randomised trial has assigned people to a napping habit and measured mortality or dementia.

Full deep dive: naps and health.