Napping and Memory: How Long to Nap and What Studies Show

A short nap really can sharpen you up. For most adults, 10 to 20 minutes in the early afternoon restores alertness without leaving you groggy, while a longer nap of 60 to 90 minutes gives the brain time for the deeper sleep that seems to help memory and learning. The catch is that napping works best as a supplement to a full night's sleep, not as a replacement for it.

Below is what the research behind those numbers actually found, how to choose a nap length that suits your afternoon, and the situations where frequent daytime sleepiness deserves a conversation with a doctor.

Why we get sleepy after lunch

The mid-afternoon slump is not just a heavy lunch talking. Two systems govern sleep. One is sleep pressure, which builds steadily the longer you are awake. The other is the circadian rhythm, the roughly 24-hour internal clock that pushes alertness up and down across the day. For many people the two line up to produce a dip in alertness somewhere between early and mid-afternoon, even after a decent night in bed.

Many cultures built their days around that dip. The siesta, a short rest after the midday meal, is still part of life in parts of Spain, Latin America and the Mediterranean, and habitual napping is common wherever the custom survives. In countries with long office hours, by contrast, an afternoon nap is often treated as a luxury or a sign of laziness. Biology does not share that view: feeling drowsy at 3 p.m. is normal, and a brief sleep is one of the most direct ways to answer it.

Some employers have taken note. Google is among the companies widely reported to have installed nap pods in its offices, and the idea of a sanctioned rest break has spread through parts of the tech and healthcare sectors, where tired staff make costly mistakes.

What the research found about naps and learning

Pilots and the 26-minute nap

One of the most cited nap studies comes from NASA. In work on long-haul flight crews published in the mid-1990s, Mark Rosekind and colleagues found that pilots given a planned rest of about 26 minutes in the cockpit showed a 34 percent improvement in performance and a 54 percent improvement in physiological alertness compared with crews who did not rest. Those figures are specific to that setting, with tired crews on long flights, but they show how much even a short sleep can restore.

Berkeley's 90-minute nap experiment

In February 2010, a team at the University of California, Berkeley, led by psychologist Matthew Walker, presented preliminary findings from a study of 39 healthy young adults. At noon, everyone did a demanding learning task designed to tax the hippocampus, the brain region that holds new facts for a short time. At 2 p.m., half the group took a 90-minute nap while the others stayed awake. At 6 p.m., both groups faced a fresh round of learning.

The people who stayed awake got worse at taking in new information as the day went on. The nappers did better than they had at noon. Brain recordings tied the benefit to Stage 2 non-REM sleep, a lighter stage that sits between deep sleep and REM. The researchers' working idea was that sleep clears the hippocampus's short-term store, moving information on to longer-term storage and making room for more. It is a tidy image, but it was a small study presented before full peer-reviewed publication, so treat it as an interesting lead rather than settled science.

Toddlers who skipped their nap

Children show the effect even more clearly. A study led by Monique LeBourgeois at the University of Colorado Boulder, published in the Journal of Sleep Research in 2012, observed toddlers aged roughly two and a half to three. Each child solved picture puzzles once after a normal nap and once after missing it. Without the nap, the children showed 34 percent fewer positive emotional responses to puzzles they could solve and 31 percent more negative responses to puzzles they could not. They also showed less confusion when a puzzle was impossible, which the researchers read as a sign they were noticing less. For young children, the afternoon nap seems to help regulate mood as well as energy.

Memory consolidation in adults

Other experiments point the same way. Naps that contain only non-REM sleep have been found to improve memory for facts, though not for motor skills. In a 2008 comparison, a 60 to 90-minute nap outperformed caffeine on several memory tasks. Together these studies suggest that longer naps do more for memory, while short naps mainly restore alertness.

How long should you nap?

The right length depends on what you need the nap to do and how much time you can spare afterwards.

• 10 to 20 minutes (the power nap). You stay in light sleep, so you wake up quickly and feel refreshed. This is the best choice if you need to be alert soon after, for a meeting, a drive or an afternoon of work. Sleep researchers generally consider five minutes too short to do much.
• About 30 minutes. This is the awkward middle. You may be slipping into deeper slow-wave sleep just as the alarm goes off, and waking from that stage brings sleep inertia, the heavy, foggy feeling that can last up to half an hour.
• About 60 minutes. A nap of this length includes slow-wave sleep, which is linked to remembering facts, names and places. Expect some grogginess on waking, so leave a buffer before anything demanding.
• About 90 minutes. This covers roughly one full sleep cycle, including REM sleep. Because you tend to wake from lighter sleep at the end of a cycle, inertia is often milder than after a 30 or 60-minute nap. It suits people who slept badly the night before, shift workers, or anyone who wants the memory and creativity benefits seen in longer-nap studies.

Studies of the post-lunch dip have found that even a 10-minute nap gives a similar lift in alertness to longer ones, so if you only have a short window, take it.

Practical tips for a better nap

• Time it early. Early to mid-afternoon fits the natural dip. Napping after about 4 p.m. makes it harder for many people to fall asleep at night.
• Set an alarm. Decide on 20 or 90 minutes in advance so you do not drift into the groggy middle zone.
• Make it easy to drop off. A dim, quiet, slightly cool spot helps. An eye mask or earplugs can make a desk or car seat workable.
• Give yourself a few minutes to wake up. Light, a glass of water or a short walk helps clear sleep inertia before you drive or make important decisions.
• Try the coffee nap if it suits you. Some people drink a coffee just before a 15-minute nap, since caffeine takes roughly that long to kick in. It works for some and not for others, and it is best avoided late in the day.

Common myths about napping

"Napping is lazy." A planned short nap is a performance tool used by pilots, doctors and athletes. Feeling drowsy in the afternoon is part of normal human physiology.

"A nap can make up for a short night." It can take the edge off, but a nap does not replace the full sequence of sleep cycles you get overnight. Regularly trading night sleep for afternoon naps tends to leave you more tired, not less.

"Longer is always better." Not for alertness. A 20-minute nap often leaves you sharper in the next half hour than a 45-minute one, because you avoid waking from deep sleep.

"Naps clear the brain like a computer reboot." The comparison is catchy, but the real picture is more nuanced. Sleep appears to help move new memories out of short-term storage, and to strengthen some of them, rather than simply wiping a slate clean.

When daytime sleepiness is a warning sign

An occasional nap is healthy. Needing one every day just to function is different. Large observational studies have linked habitual naps of more than an hour, especially in older adults, with higher rates of heart disease, type 2 diabetes and depression. These studies show an association, not cause and effect: long daytime sleep may simply be a sign of poor sleep at night or of an illness that is already present.

If you often fall asleep without meaning to, snore loudly, wake up unrefreshed after a full night, or find that naps are pushing your bedtime later and later, talk to a doctor. Persistent sleepiness can have treatable causes, and a professional can help you find out what is going on.

The simplest rule is still the best one: protect your night's sleep first, and use a short afternoon nap as a bonus when you need it.

Sources: UC Berkeley News (2010): naps boost learning capacity; ScienceDaily (2012): CU Boulder study of nap-deprived toddlers; Wikipedia: Nap (NASA study, nap lengths, sleep inertia); Sleep Foundation: Napping; Natural Society (original reference).

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