Naps: how long they should last and when, according to the research

How long it should last: the benefits measured in the lab

A key experiment compared naps of exactly 5, 10, 20 and 30 minutes of sleep, at 3 p.m., with not sleeping. The participants were 24 young adults who slept well, didn't usually nap and had slept about five hours the night before. The 10-minute nap improved every measure right from the start—measured and perceived sleepiness, fatigue, vigor and test performance—and was, according to the authors, the most effective of those they tested; the table sums up the rest.¹

A few seconds aren't enough: in another experiment by the same group, with 16 young adults who had slept from midnight to 5 a.m., falling asleep for 30 or 90 seconds improved nothing measurable, and 10 minutes did.² A practical detail: in the duration experiment, minutes of sleep were counted, not time lying down; however long it takes you to fall asleep comes on top of that.¹

The SES speaks of “a certain consensus”: short naps, of less than 20 to 30 minutes, improve alertness and performance without harming nighttime sleep, something it considers especially clear in students, older people and shift workers; and it recommends limiting them to a maximum of 20–30 minutes after lunch.⁵

Why a long nap can leave you feeling worse

The grogginess on waking has a name: sleep inertia, a spell of sleepiness, disorientation and poorer performance. In studies it usually wears off in less than 30 minutes, sometimes in 15, although full recovery can take longer. It's greater if you've slept little beforehand or had been awake for many hours, and if you wake up in the middle of your biological night.³

In afternoon naps, deep sleep and inertia tend to increase with length, although the exact role of deep sleep hasn't been confirmed. That's why researchers propose short naps to reduce inertia, but no length always prevents it: a 10-minute nap at 7 a.m., after staying awake all night in a simulated night shift, produced it too.³

Inertia doesn't cancel out the benefit: once that spell has passed, a nap with deep sleep can reduce sleepiness for longer.⁸ What matters is what you have to do right after you get up; the same review reports real consequences of inertia in tasks where safety depends on being alert.³

What about the hour-and-a-half nap? The SES advises, if you're very sleep-deprived, sleeping about 90 minutes in a row so as to wake up at the end of a complete sleep cycle.⁵ The idea is to wake up at the end of a cycle, in light sleep. But the review on inertia finds contradictory results on whether the sleep stage you wake up from determines it,³ and among the sources reviewed for this article there's no experiment comparing that length with a short nap.

When to nap, and what happens to your night

Drowsiness after lunch isn't due to the meal alone: the body clock has a natural dip in alertness after lunch, in addition to the one at night.⁸ The SES places it about eight hours after waking up, when accumulated sleep pressure adds to that dip.⁵ If you get up at 7 a.m., it falls around 3 p.m., the time of the naps in the duration experiment.¹

Does it take sleep away from the night? Less than is often said. A review on sleep hygiene concludes that most studies, done mainly with older people, find no major relationship between napping and nighttime sleep, either in what people report or in what devices measure, although the data aren't entirely consistent.⁶ In nine healthy people aged 74 to 87, two weeks of a daily 90-minute nap in the early afternoon led, in the laboratory, to nighttime sleep about 48 minutes shorter, somewhat less efficient and with earlier awakenings; in their diaries, however, there were no differences, and the authors themselves considered those effects small.⁶⁷

There are few studies on timing, and they don't agree. In healthy young adults, a single nap at dusk worsened several aspects of that night's sleep, including total sleep time and how long it took to fall asleep; in postmenopausal women, on the other hand, those who napped at dusk woke up earlier, but their nighttime sleep was more efficient according to activity recordings.⁶ The explanation for why a nap can take away from the night is sleep pressure: sleeping during the day releases it, sometimes so much that nighttime sleep suffers hours later.⁸

The SES guidance is practical: avoid napping if it contributes to having more trouble sleeping at night or to shorter, more fragmented sleep.⁵ If that happens to you, our suggestion—an inference, not a study finding—is to try napping earlier or for less time before dropping the nap altogether.

If napping is how you make up for short nights, it's worth looking at the root of it: cutting back on the night isn't a good way to gain time, as we explain in the minimums that count when you're short on time, and sleeping differently on weekdays and weekends has its own effects, which we review in the article on weekend sleep. And if what you do to get through the afternoon is have another coffee, caffeine and sleep has its own fine print.

Long naps and health: association, not cause

A meta-analysis of 11 cohort studies, with 151,588 people followed for an average of 11 years, found that napping for an hour or more a day was associated with 82% more cardiovascular disease (with a wide margin of uncertainty: between 22% and 171% more) and 27% more mortality than not napping; naps of less than an hour were associated with neither. In the analysis by length (a curve fitted to the studies' categories), cardiovascular risk was lowest at around 30 minutes a day and rose steeply above about 45, although the authors call for more studies before attributing a benefit to short naps.⁹ These are relative risks: they say how much more frequent the problems were in one group than in another, not the probability that they will happen to a given person.

The relationship isn't the same for everyone. In a study of 116,632 people aged 35 to 70 from 21 countries, followed for a median of 7.8 years, napping was associated with more deaths and cardiovascular events only in those who slept more than six hours a night; in those who slept six or fewer, it wasn't. The authors suggest two readings: in people who sleep little, napping might compensate; in those who already sleep enough, sleeping more during the day could be an early sign of poorer health.¹⁰

In Spain, a cross-sectional study of 3,275 adults from a Mediterranean population in which the siesta is part of the culture (the ONTIME study, led from the University of Murcia) found that 35% usually napped and 16% took long naps, of more than 30 minutes. Long naps were associated with higher weight, waist circumference, blood glucose and blood pressure than not napping; short ones, with a lower likelihood of having high systolic blood pressure. Part of the relationship with weight ran through other habits: smoking more, sleeping and eating later, and eating more at midday.¹¹

Why not conclude that long naps are bad? Because the direction may be the reverse. People who sleep poorly at night or have a health problem may be sleepier during the day and take longer naps.⁵⁸ In a case-control study in Cáceres, people who habitually napped more often had sleep apneas, and the relationship between napping and high blood pressure disappeared when the apneas were taken into account; the authors propose seeing the nap as a possible marker, not as the cause.¹² The authors of the meta-analysis also acknowledge that possibility.⁹

How to find the nap that suits you

What follows is our reading of the sources, not a guideline that has been tested as such:

• If you want to feel more alert, start short: 10 to 20 minutes of sleep, with an alarm. The 10-minute nap gave the best result in the key experiment, and both fit within the SES limit.¹⁵
• Better in the early afternoon than at the end of the day.⁵⁶
• If you have something demanding right afterward, such as driving, allow a few minutes for the grogginess to pass.³
• If you notice your nights getting worse, the SES advises avoiding naps.⁵ Before dropping them altogether, try napping earlier or for less time: that's our own inference, not a study finding.

Treating it as a test lasting a few weeks, with one or two things written down, keeps you from drawing conclusions from a single day; in how to turn a wellness data point into a question and a test we explain how to do it without turning it into another chore.

When it's not about naps

Feeling sleepy after lunch is normal. Being very sleepy during the day is something else: it can have very different causes, such as sleeping too little, shift work, some medicines or sleep problems, and excessive sleepiness with no known cause can be a sign of a sleep disorder.¹³ If this happens to you, or if you suddenly need long naps every day even though you sleep well at night, see a health professional. This article can't be used to assess the cause.

If you work shifts or nights, napping follows other rules: the SES suggests, for example, a nap before a night shift and, if possible, another short one in the early morning hours.⁵ This article doesn't cover that case.