All your questions about napping, answered 

About 20 years ago, before she became a prominent sleep researcher, Cátia Reis studied marine biology at the University of Lisbon. She also worked full time as a flight attendant for TAP Air Portugal, chartering passengers around the region late at night and early in the morning before classes. 

The schedule left her profoundly sleep-deprived. 

“I was questioning what was happening to me because I was so, so tired,” Reis recalled. “I even fell asleep during a takeoff. You can imagine my degree of deprivation.”

At the time, scientists knew naps offered some temporary benefits for pilots, shift workers and others who couldn’t sleep enough at night. But important questions remained about the ideal timing and duration of a nap, why people responded differently to daytime sleep and whether napping could improve long-term health.

Reis set out to answer those questions. After graduating in 2008, she studied sleep and fatigue among airline pilots for Portugal’s civil aviation authority before becoming a chronobiologist, researching sleep and circadian rhythms and helping shift workers manage sleep deprivation.

Over the course of Reis’s career, researchers have learned much more about how naps can improve alertness, memory, mood and performance and how their effects vary with timing, duration and individual sleep needs. They have also found the limits of napping: While a nap can help someone recover from an occasional bad night of sleep, experts told Straight Arrow a nap should not be treated as a routine replacement for sufficient nighttime sleep. 

But the more scientists learned, the clearer it became that napping and sleep needs are highly individual and are shaped by a huge range of factors, from age and work schedule to diet, exercise and chronotype — whether someone is naturally a morning person or a night owl. With the help of smartwatches and increasingly sophisticated algorithms, researchers are now working to tailor sleep guidance and help each person determine when and for how long they should nap.

What can a nap actually do for you?

Decades of research suggest that a short, well-timed daytime sleep can reduce sleepiness and improve certain aspects of mood and mental performance, including alertness, attention, reaction time and memory, according to Kimberly Cote, a professor of psychology and neuroscience at Brock University in Ontario, Canada. 

In 2022, three researchers from the National University of Singapore combined data from 54 prior studies and found that people who took afternoon naps performed slightly better on several cognitive tests compared with those who did not nap. The clearest benefits appeared in alertness and attention, processing speed and memory, regardless of a napper’s age or nap duration. A similar review conducted the year prior also concluded that daytime naps — even those as short as six minutes — help the brain retain newly learned information.

Sleep helps consolidate memories, moving newly learned information from temporary storage into a more stable form that is easier to retrieve, said Rebecca Spencer, a professor in the University of Massachusetts Amherst’s Department of Psychological and Brian Sciences.

Processing recently formed memories also frees the brain to absorb new information, she explained.

“You now have a clean slate in your short-term memory storage to take on new memories so it’s going to promote new memory formation,” Spencer said. Sleep performs a similar function for emotions, helping the brain process the morning’s experiences, for instance, so they exert less influence over how someone responds to events later in the day. That processing may contribute to improvements in emotional regulation, creativity and decision-making. 

“In terms of cognitive performance, we know that reaction time improves attention and memory, for example,” said Cote. “This is going to translate to better on-the-job performance and better driving performance.” 

Naps are particularly valuable when lapses in attention carry major consequences. 

As Reis knows all too well, airline staff are also frequently exposed to sleep deprivation and irregular sleep schedules. Napping can help. In a NASA field study of long-haul flight crews, pilots who were allowed a planned rest period slept for an average of about 26 minutes. Afterward, they maintained more consistent performance and displayed fewer physiological signs of sleepiness than pilots who did not nap.

Reis said fatigue can become especially dangerous near the end of a night shift or during the commute home, as workers’ attention declines after many consecutive hours awake. A review of 18 studies that covered nearly 500 people on the night shift — both real and simulated in a laboratory — found an overall improvement in cognitive performance following a nap.

Researchers have also examined whether napping might influence longer-term health, including the risk of chronic disease. Here, however, the evidence is murky — and sometimes contradictory. 

Are there long-term health benefits of napping? 

While a handful of studies suggest napping may protect against obesity, diabetes and cardiovascular disease, others have associated naps with an increased risk of those conditions and even premature death.

In 2022, researchers in China and Finland reviewed nearly 100 studies and found that naps lasting an hour or longer were associated with higher rates of cardiovascular disease and mortality. Shorter naps, particularly those under 30 minutes, were not linked with poor health outcomes. The researchers cautioned that much of the available evidence was weak or suggestive, rather than conclusive. 

Other reviews have identified similar patterns. A 2023 analysis of more than 170,000 individuals revealed that people who napped had a higher risk of obesity compared with those who didn’t nap; however, a smaller subanalysis found that the risk was higher among those who took naps longer than one hour. That same year, another research group reviewed 40 observational studies and found that habitual napping was linked to a higher risk of diabetes, but there was no significant relationship for naps shorter than 30 minutes.

On the other hand, one 2019 study followed more than 3,400 Swiss adults for about five years, and found that those who never napped were nearly twice as likely to experience a cardiovascular event — such as a heart attack or stroke — as those who napped once or twice a week.

An August study led by Marta Garaulet, a professor of physiology at Spain’s University of Murcia, followed 872 adults with coronary heart disease for seven years, grouping them as non-nappers, short nappers who slept for 30 minutes or less or long nappers who slept for more than 30 minutes. Researchers measured participants’ blood pressure and body size and took blood samples at the beginning of the study and during annual visits. 

Over the study period, habitual short nappers generally had healthier measures of body weight, waist size, blood sugar, insulin response and blood fats linked to heart disease. The differences were most consistent when short nappers were compared with long nappers. However, the study was observational and did not prove that short naps caused those differences or prevented heart attacks and strokes, Garaulet explained. 

She said the contradictory findings around obesity and other chronic diseases may arise because researchers often treat all daytime sleep as the same behavior. 

“The biggest misconception is that all naps are biologically equivalent and can simply be classified as ‘good’ or ‘bad,’” she said. 

The timing and duration of a nap seem to matter. A brief, planned nap taken out of habit or enjoyment may be very different from a longer nap prompted by inadequate nighttime sleep, medication use, illness or an undiagnosed sleep disorder. 

The direction of cause and effect is also difficult to determine. Over the past 10 to 15 years, research has increasingly connected chronic sleep deprivation — not necessarily napping itself — with poorer cardiovascular and metabolic health, Cote said. In some studies, napping may therefore be a sign that participants are chronically sleep-deprived, meaning researchers could be detecting the health risks associated with inadequate sleep rather than an effect of the naps themselves. 

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“You might see this association between people who take naps and poor long-term health outcomes like cardiovascular health, and so you think, ‘Oh my gosh, are naps bad for you?’” Cote said. 

“Well, no, naps aren’t bad for you. The confound there is that unhealthy people are both more likely to take naps because they’re sleepy and more likely to have heart attacks,” she said. “It doesn’t necessarily link a causal link between the naps and the heart attack.”

Garaulet agreed that this phenomenon, known as reverse causation, probably explains some of the troubling associations but may not explain everything. Garaulet pointed to genetic analyses suggesting that a predisposition toward longer daytime sleep may contribute to higher blood pressure and a larger waist circumference. Her team has also observed associations between long naps and poorer metabolic health among relatively young Mediterranean adults without diagnosed disease, for whom taking a siesta is an established cultural practice rather than necessarily a response to illness.

Those results still fall short of proving that long naps cause health problems. 

“Genetic evidence is not equivalent to a randomized clinical trial, and residual confounding remains possible,” Garaulet said.

That is why researchers increasingly argue that studies must consider not only whether someone naps, but also how long and when they sleep, how frequently they nap, whether they sleep well at night and what prompts them to lie down during the day. 

“Two naps may look identical in terms of duration, but their biological origins — and therefore their potential health implications — may be very different,” said Garaulet.

The way nap studies are designed may also obscure those differences. To compare results across participants, researchers generally place naps into standardized categories — such as shorter or longer than 30 minutes — even though people differ in how much sleep they need, how quickly they fall asleep and which sleep stages they enter during that time. 

For now, Cote said the clearest advice is to focus on attaining sufficient sleep overall. 

“Everything we know about performance, naps are great for you,” she said. “In terms of long-term health, get the sleep that you need. If someone is chronically restricting sleep, that is something that in a large group of people we see is going to be more linked to poor health outcomes in the long term.”

Can a nap make up for a bad night’s sleep? 

Researchers do not yet know whether naps might help prevent the long-term health consequences of chronic insufficient nighttime sleep. But a nap can provide a short-term boost after an occasional bad night.

In one 2006 study, 24 healthy young adults who were not habitual nappers restricted their nighttime sleep to about five hours and then, on separate occasions, either did not nap or slept for precisely five, 10, 20 or 30 minutes at 3 p.m. Researchers monitored them for three hours afterward. 

The five-minute nap produced few benefits, while the 10-minute nap immediately improved sleepiness, fatigue, energy and cognitive performance, with some effects lasting more than two hours. Benefits from the 20-minute nap emerged after about 35 minutes and lasted as long as two hours. The 30-minute nap initially impaired alertness and performance — an effect known as sleep inertia — but was followed by improvements lasting up to two-and-a-half hours. Overall, the 10-minute nap produced the most immediate and consistent benefits, although the study was small and involved only young, otherwise healthy sleepers. 

“If you’ve had one bad night of sleep, absolutely, a quick daytime nap, 20 to 30 minutes, will lead to some improvements in alertness and attention and performance and well-being,” said Cote. “You’re going to feel some benefit, and if you can make the time to have a safe nap somewhere, then that’s a lot better than dragging through the day on your sleep debt.”

But feeling and functioning better does not necessarily mean the body has recovered everything it missed overnight. 

“A nap can complement nighttime sleep and partially compensate for occasional sleep loss, but it should not routinely replace adequate nighttime sleep,” Garaulet said. 

Spencer agreed that, for most adults, obtaining sleep in one uninterrupted period has advantages. During a long night, the brain moves repeatedly between cycles of light sleep, deep sleep and rapid eye movement, or REM, sleep. Together, those stages support processes ranging from physical recovery and immune function and allow deeper processing of memories, allowing the brain to connect new memories with older knowledge, identify patterns and form broader understanding. A daytime nap may include some of the same stages, particularly if it is long, but it cannot reproduce the full duration, continuity or circadian timing of a sufficient night’s sleep, Garaulet said.

Still, Spencer cautioned against treating daytime sleep as inadequate. 

“A lot of these functions that we see for overnight sleep on cognition have been also shown with naps,” she said. “There are many people that can’t get that contiguous sleep bout for one reason or another, and certainly supplementing it by having midday sleep is useful to them, even if not optimal.”

For people who routinely need naps because they are not sleeping enough at night, Cote said they should prioritize identifying and addressing what is cutting that sleep short. 

“If you’re intentionally having a short nighttime sleep and trying to compensate on a regular basis, that’s not good,” she said. “That consolidated, regular, uninterrupted night of sleep is ultimately the best sleep that you can get.”

What about shift workers?

While prioritizing sufficient nighttime sleep may be realistic for some people, it is often impossible for shift workers, pilots, athletes and others whose schedules conflict with the body’s internal clock. These are the populations Reis works with today to develop practical strategies for managing sleep deprivation and fatigue. 

When Reis studies shift workers, she considers all the sleep they obtain over 24 hours rather than looking only at their primary sleep period. A worker might sleep after returning home in the morning and then take another nap before the next night shift. For someone who cannot sleep while working, Reis may recommend a long nap before the shift. This reduces the number of consecutive hours the worker must remain awake, helping to preserve attention later in the shift and during the commute home, when fatigue-related accidents are a particular concern. 

Even people who consistently work nights rarely shift their circadian rhythms completely to adjust to daytime sleeping, Reis said. And that’s mostly because “people are living in a society.” On their days off, most return to daytime routines to spend time with family and friends, repeatedly moving their sleep schedules back and forth. 

Naps cannot remove all the strain of that irregularity, but Reis considers them preferable to remaining chronically sleep-deprived. 

“For those people who are not able to cope truly with society — because they are an athlete or a shift worker or an extreme chronotype — that can be a very good option,” she said. “It’s much better to do something like that and actually be rested and try to fulfill your sleep needs than be sleep-deprived all the time.”

How to take the ideal nap — and prevent groggriness

For most healthy adults who keep regular nighttime hours, early afternoon is generally the best time to nap, Cote said. By then, a person has been awake long enough to build pressure to sleep, while bedtime remains far enough away that a nap is less likely to interfere with nighttime rest. Spencer recommends avoiding naps after about 4 p.m., when the body may begin treating daytime sleep more like the start of a full night’s rest, increasing grogginess and potentially disrupting sleep later that night.

Work schedule and chronotype can alter that advice, Reis said. A late chronotype, or “night owl,” who must report for an early-morning shift may be unable to fall asleep early enough the previous night, for example. Reis sometimes advises people in that situation to approach the early shift more like an overnight shift and plan naps as a strategic countermeasure.

Cote recommends limiting a nap to approximately 20 minutes of actual sleep. A person who needs 10 minutes to drift off might therefore reserve half an hour for a nap and set an alarm. Keeping the nap brief reduces the likelihood of entering deeper sleep, which can make waking more difficult, and helps preserve the sleep pressure needed at night.

Spencer, however, cautions that the science does not support one universally ideal duration. Although studies have found benefits from naps as short as six or 10 minutes, reviews of the evidence do not consistently identify 20 to 30 minutes as a “magic number,” she said. Instead, the appropriate duration depends on the person and the purpose of the nap.  

“My recommendation in terms of what you need for a nap is going to be different depending on what you’re trying to get out of it,” Spencer said. Someone seeking a quick increase in alertness before returning to work may choose a shorter nap, while someone recovering from lost sleep, illness or strenuous exercise may benefit from more time. 

Spencer offered her own previous night as an example: Her sick dog had disrupted her sleep, leaving her with roughly five hours instead of her usual six to seven. Based on that shortfall, she considered giving herself an hour to nap to make up for her “sleep debt.” A 20- or 30-minute window would not necessarily provide enough recovery, she said.

Spencer cautioned that the oft-cited recommendation to get seven to nine hours of sleep at night is also a bit of a myth. Sleep needs vary from person to person, so people should also consider signs of sleep deprivation — such as difficulty waking, persistent daytime sleepiness, struggling to stay awake during meetings or napping unintentionally — when deciding whether and for how long to nap. 

Reis recommends comparing the number of hours you sleep during the work week with days when sleep tends to be less restricted. Someone who claims to function well on five hours of sleep during the week but sleeps for 10 hours without an alarm on days off is probably not sleeping enough during the week, she said. Lengthier sleep on free days suggests the person has been accumulating a deficit. One of the clearest ways to estimate individual sleep needs is to observe how long you naturally sleep during a holiday or another period without alarms — and whether you feel alert during the day.

A nap may also help before an anticipated late night, although Spencer said it is more accurate to think of paying off existing sleep debt than “banking” extra sleep. Sleep cannot necessarily be stored in advance, though this is an area of active debate among sleep scientists. 

But even if you cannot “presleep,” a nap can help begin the night as well-rested as possible. 

“A better way to think about it in terms of what we are actually capable of doing is not overfilling the gas tank, not really banking sleep, but just making sure we’re not in debt to sleep,” Spencer said.

Can you prevent post-nap grogginess?

Individual differences also help explain why some people wake from a nap refreshed while others remain groggy, a temporary effect known as sleep inertia. Someone who is sleep-deprived may enter deeper sleep more quickly and have greater difficulty waking, Spencer said. 

Nap frequency also matters. Spencer knows professors who sleep for 45 minutes on their office couches at the same time each day and can wake up ready to resume work because they have incorporated the nap into their circadian rhythm.

Spencer advises athletes considering a nap before a competition not to make game day the first time they test the strategy. Instead, she tells them to nap consistently enough to learn how their body responds and how much time they need to become fully alert. 

If grogginess persists after waking, Spencer recommends people expose themselves to light, go outside if possible and move around rather than remaining seated. Caffeine may help, but its effects can take about 45 minutes to appear and remain for six to eight hours, so consuming it later in the day could interfere with nighttime sleep. 

Spencer also recommends making a nap feel different from protected nighttime sleep. Rather than trying to recreate a completely dark, silent bedroom during the day, she suggests allowing some light or background noise. Those environmental cues can help the brain distinguish a daytime nap from the longer sleep period reserved for night, and reinforce a stable sleep-wake rhythm.

Though broad patterns are emerging in the research, napping remains highly individual, Spencer said. Understanding your own sleep needs, noticing how your body responds to naps of different lengths and considering what you hope to gain from the rest can help you tailor a nap that works for you. 

“The truth is, it is a complicated thing because people nap for so many different reasons,” she said.

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