Short naps restore alertness, while long ones can be a warning sign

Key takeaways

• In a NASA study published in 1994, airline pilots given a planned rest over the Pacific fell asleep in under 6 minutes, napped about 26 minutes and showed fewer signs of drowsiness through landing¹.
• Short naps work fastest: after a short night, a 10-minute nap helped sooner than a 30-minute nap, whose benefits came later, likely because of grogginess on waking³.
• In a small 1997 driving-simulator study, caffeine followed by a nap of under 15 minutes cut driving incidents to 9% of the placebo level⁵.
• Long naps go along with higher rates of heart disease and early death, but a 2026 review of 16 meta-analyses found none of those links strong and said they can’t show cause⁷⁸.
• In older adults, naps that grow longer or more frequent can sometimes be an early sign of illness, including Alzheimer’s disease, so mention the change to a clinician¹¹¹³.

Picture a Boeing 747 cruising high over the Pacific. One of the three pilots on the flight deck leans back and, by plan, goes to sleep¹.

It was a NASA experiment. Researchers from NASA Ames Research Center flew with 21 pilots on a 12-day trans-Pacific trip¹. Twelve got a planned 40-minute rest during the quiet cruise part of each studied flight, one pilot at a time. Nine did not¹.

The resting pilots fell asleep in 5.6 minutes on average and slept about 26 minutes¹. In the last 90 minutes of flight, including descent and landing, brain-wave recordings caught fewer than half as many brief lapses into drowsiness in the nappers as in the others¹.

Napping is one of the oldest and cheapest forms of self-care. In a 2025 survey for the American Academy of Sleep Medicine (AASM), 46% of U.S. adults said they nap to stay alert¹². Below, we cover how to nap well, and how to tell when a growing need for naps is telling you something.

The NASA study is real, but its most-quoted numbers are harder to find

You may have read that NASA’s nap improved pilot performance by 34% and alertness by 54%. The 1994 report says the nap was tied to better alertness and performance, but neither its abstract nor the sections we checked state those percentages¹. A 2026 aviation trade article traces them to a shorter 1995 summary by the same researchers².

The closest match in the report is the count of “microevents,” the brief bursts of drowsiness seen on brain-wave and eye recordings. Pilots who didn’t rest averaged 6.37 per person in the final stretch of flight, and nappers averaged 2.90¹. That’s about 54% fewer, by our arithmetic.

Reaction-time tests told a similar story. The pilots who didn’t nap got slower as the trip went on, while the nappers held steady¹. On night flights, attention lapses on that test rose twice as much in pilots who didn’t nap¹.

The report’s authors were careful about limits. The nap was a short-acting fix: it didn’t shrink the pilots’ built-up sleep debt¹. The study covered one airline on one route pattern, with NASA observers on the flight deck¹.

Today, European aviation rules allow “controlled rest” in the cockpit of up to 45 minutes, followed by about 20 minutes to recover, and several other countries allow it, too². The Federal Aviation Administration has not approved planned naps for U.S. airline crews².

Ten to 20 minutes is the sweet spot for a quick boost

The catch with napping is sleep inertia, the groggy, slow feeling right after you wake. The NASA authors noted that a nap under an hour is enough and that longer naps raise the odds of deep sleep and grogginess¹. They built in 20 minutes of recovery before pilots went back to work¹.

A 2001 study in the journal SLEEP compared a 10-minute and a 30-minute afternoon nap in people who had slept less than usual the night before³. The 10-minute nap eased the effects of short sleep more quickly, within the hour after waking³. The 30-minute nap’s benefits came later, likely because of sleep inertia³.

The National Heart, Lung, and Blood Institute (NHLBI) suggests keeping naps to no more than about 20 minutes and avoiding them after 3 p.m., especially if you have trouble falling asleep at night⁴.

Timing matters, too. A 2026 umbrella review, a review of other reviews, included a pooled analysis of 18 randomized trials⁸. Naps taken between 12:30 and 4:50 p.m., most often around 2 p.m., after a normal night’s sleep improved performance on thinking tests⁸.

That window lines up with the early-afternoon dip in alertness that our article on sleep pressure explains. Our article on sleep and memory covers what naps do for learning.

Coffee, then a nap: the “caffeine nap” has a small study behind it

Caffeine takes about 30 minutes to kick in, according to a CDC training course for nurses from the National Institute for Occupational Safety and Health (NIOSH)⁶. That delay is the idea behind a caffeine nap: drink a coffee, nap briefly, and wake as the caffeine starts working.

A 1997 study in the journal Psychophysiology tested it⁵. Twelve sleepy adults took a 30-minute break before a dull, two-hour afternoon drive in a car simulator⁵. During the break they got a placebo, 200 mg of caffeine, or caffeine plus a nap of under 15 minutes⁵.

On the placebo, driving incidents and sleepiness peaked in midafternoon⁵. Caffeine alone cut incidents to 34% of that level. Caffeine plus the nap cut them to 9%⁵. Even people who only dozed, without true sleep, got the benefit⁵.

NIOSH suggests the same combination to drowsy drivers as a temporary fix, not a substitute for sleep⁶. It’s one small study in a simulator, so call it promising but early. Mind the timing, too: a midafternoon caffeine nap can still be in your system at bedtime, as our article on caffeine timing explains.

Plan your nap

This planner is our own tool, built from the studies above. Pick your purpose, then read across.

Your purpose	How long	When	Watch out for
A quick lift on an ordinary day	10 to 20 minutes34	Early to mid-afternoon, before 3 p.m.48	Longer naps can leave you groggy at first13
Getting through the day after a short night	About 20 minutes; keep it well under an hour147	Early afternoon	A nap won’t erase your sleep debt1
Drowsy behind the wheel	15 to 20 minutes, right after caffeine if you use it46	As soon as you notice; pull off somewhere safe	The lift is temporary; plan real sleep6
Can’t fall asleep	Rest with eyes closed for 15 to 20 minutes	Same as above	Dozing still helped in the driving study5
Night shifts or rotating shifts	See our article on irregular schedules	Before the shift	Drowsy commutes after night work14

A few habits help any nap. These are our suggestions:

1. Set an alarm. For a 10- to 20-minute nap, set it for about 20 to 25 minutes to leave time to drift off. The NASA pilots took about 6 minutes¹.
2. Find a dark, quiet spot. Lie back or recline; an eye mask works in a car or office.
3. Give yourself a few minutes to recover before driving or doing anything risky. NASA allowed 20¹.
4. Skip it late in the day if you have trouble sleeping at night⁴.

Long naps track with heart disease and early death, but that doesn’t prove they cause them

At the European Society of Cardiology’s 2020 congress, Zhe Pan of Guangzhou Medical University presented a pooled analysis of more than 20 studies and 313,651 people, about 39% of whom napped⁷. The longest nappers fared worst. Compared with people who didn’t nap, those whose naps ran past an hour had a 30% higher risk of death from any cause, and their risk of cardiovascular disease was 34% higher⁷. Naps shorter than an hour weren’t tied to heart disease⁷.

The picture shifted once night sleep entered the math. The extra death risk from long naps showed up only among people who also slept more than six hours at night⁷. For people who don’t nap, Pan saw no strong reason to begin⁷.

A 2026 umbrella review in Public Health Reviews pooled 16 meta-analyses⁸. Any napping was linked with a 22% higher risk of death, and naps over an hour with a 15% higher risk⁸. Napping also tracked with stroke, heart disease, high blood pressure and type 2 diabetes⁸.

But the authors rated none of these links as strong or highly suggestive, and most were weak⁸. Half of the reviews they pooled were rated critically low in quality⁸. They wrote that the findings can’t be read as cause and effect, because night sleep quality, social and economic status, and the severity of other illnesses could explain them⁸.

The review has loose ends, too. Its abstract ties some risks, such as 30% more coronary heart disease, to naps over an hour, while its results report that figure for napping in general⁸.

This is the plain-language version. Researchers call it confounding when a third factor, such as poor health, drives both the napping and the disease. Reverse causation, our explanation here, means the illness comes first: a person with undiagnosed sleep apnea or heart trouble may feel tired and nap more. Either way, the nap can be a signal rather than the cause.

Where the siesta is ordinary, a nap may mean less

The 2026 review notes that habitual napping is more common in China and in parts of Europe, including Greece and around the Mediterranean⁸. Its findings also varied by region. Napping was linked with type 2 diabetes and obesity in European and U.S. groups, but not in Chinese groups⁸.

The authors pointed only to cultural norms and lifestyle, and noted that the studies didn’t explore the gap in depth⁸. One possible reading, which is ours and hasn’t been tested: where healthy people nap by custom, a nap is less likely to flag hidden illness. In places where adults rarely nap, a daily nap may more often mean something is wrong.

Many traditions build rest into the middle of the day, and natural-health readers often see that as wisdom modern work schedules lost. The trial evidence supports the short version of that wisdom: a brief afternoon rest helps alertness⁸. What the research questions is the long, unplanned nap that creeps in with age or illness. Pan’s advice for anyone who enjoys a siesta was to keep it under an hour⁷.

In older adults, a growing nap habit can be an early warning

In 2022, researchers from UC San Francisco, Brigham and Women’s Hospital and Rush University reported on 1,401 older adults, average age 81, followed for up to 14 years¹¹. Each year, participants wore a watch-like device for up to two weeks to track daytime naps¹¹.

People whose thinking stayed sharp added about 11 minutes of daytime napping each year¹¹. The yearly increase rose to 24 minutes once mild cognitive impairment was diagnosed and to 68 minutes after an Alzheimer’s diagnosis¹¹. Among people who started out with normal thinking, those who napped more than an hour a day had a 40% higher risk of developing Alzheimer’s than those who napped less¹¹.

The link held after the team accounted for night sleep¹¹. Co-senior author Yue Leng of UCSF said the evidence can’t yet show that napping causes dementia, and that heavy napping may signal faster brain aging¹¹. A 2019 UCSF study found fewer wake-promoting nerve cells in the brains of people with Alzheimer’s, which could explain extra napping¹¹. The National Institutes of Health and the BrightFocus Foundation funded the work¹¹.

A 2023 study pointed the other way for regular nappers. Researchers at University College London and partners used Mendelian randomization, a method that uses gene variants linked to a habit as a kind of natural experiment⁹¹⁰. In UK Biobank data from up to 378,932 people, a genetic tendency to nap habitually went with brains about 15.8 cubic centimeters larger⁹. That’s roughly 1.3%, which the authors equate to 2.6 to 6.5 years of age-related shrinkage¹⁰.

It found no link with the hippocampus, a memory center, or with reaction time or visual memory⁹. Napping was self-reported and measured only by frequency, not length, and the authors want the result repeated in other ancestries and age groups¹⁰. We rate it promising but early. The two studies can both be true: regular short naps may help, while a sudden change in napping deserves attention.

Naps on the road and on the night shift

Our article on the consequences of short sleep covers how often drowsy drivers crash, and why the count is hard to pin down. The AASM notes that people often can’t judge how tired they are¹⁴. So watch for the signs instead: constant yawning, heavy eyelids, drifting from your lane, missing turns and not remembering the last few miles⁴¹⁴.

If you notice them, pull off somewhere safe and nap for 15 to 20 minutes, with a caffeinated drink first if you use caffeine⁴⁶. Opening the window or turning up the radio won’t fix real sleepiness, and even a little alcohol makes it worse⁴. Shift workers and anyone short on sleep face higher risk¹⁴. Our article on irregular schedules covers naps before and during night shifts.

What the evidence says, rated

Claim	What studies found	Evidence level
A short afternoon nap improves alertness and performance	18 randomized trials pooled, plus the NASA field study18	Strong evidence
10 minutes beats 30 minutes for a quick lift	Small lab study after short sleep3	Promising but early
Caffeine plus a short nap beats caffeine alone	One 12-person simulator study5	Promising but early
Regular napping keeps the brain larger	One genetic study with a modest effect9	Promising but early
Long naps cause heart disease or early death	Observational links rated weak; confounding likely78	Not enough evidence
Napping causes Alzheimer’s disease	Observational; napping may partly be an early symptom11	Not enough evidence
A nap can replace lost night sleep	NASA naps didn’t reduce sleep debt; NHLBI says naps don’t replace night sleep14	Evidence says no

Questions readers ask

The bottom line

A short nap is free, natural and well supported. Ten to 20 minutes in the early afternoon can restore alertness, and a coffee just before can add to the lift when a drowsy driver has pulled over to recover.

Long naps are a different matter. They track with heart disease, early death and Alzheimer’s, though poor health and poor night sleep may explain much of that link. Keep naps short, don’t use them to replace night sleep, and treat a new or growing need for naps as a reason to see a clinician.

Related reading

• A big caffeine dose 12 hours before bed can still cut deep sleep
• Sleep pressure builds all day, and your body clock decides when it wins
• One in seven workers clocks in during off-hours, and sleep is the first thing to anchor
• Two weeks of six-hour nights can impair you like an all-nighter
• Sleep, food and easy days beat most recovery gadgets

Sources

1. Rosekind MR, Graeber RC, Dinges DF, et al. “Crew Factors in Flight Operations IX: Effects of Planned Cockpit Rest on Crew Performance and Alertness in Long-Haul Operations.” NASA Technical Memorandum 108839 (DOT/FAA/92/24), NASA Ames Research Center, 1994. ntrs.nasa.gov
2. William H. “Pilots are sleeping in the cockpit: why EASA allows naps but FAA says no.” Aviation A2Z, August 30, 2026. aviationa2z.com
3. Tietzel AJ, Lack LC. “The short-term benefits of brief and long naps following nocturnal sleep restriction.” SLEEP, 2001;24(3):293 (abstract record). synapsesocial.com
4. National Heart, Lung, and Blood Institute. “Your Guide to Healthy Sleep.” NIH Publication No. 11-5271, revised August 2011. nhlbi.nih.gov
5. “Suppression of sleepiness in drivers: combination of caffeine with a short nap.” Psychophysiology, 1997;34(6):721-725 (PubMed record). pubmed.ncbi.nlm.nih.gov
6. National Institute for Occupational Safety and Health. “Work Hour Training for Nurses, Module 11: Preventing Crashes.” CDC, accessed October 2026. cdc.gov
7. European Society of Cardiology. “Long naps may be bad for health” (on Pan Z, et al., published in Sleep Medicine, 2020;74:165-172). Press release, August 26, 2020. escardio.org
8. Du P, Li J, Hua Z, et al. “Multiple Health Outcomes of Daytime Napping: A Comprehensive Umbrella Review.” Public Health Reviews, 2026;47:1609013. public-pages-files-2025.ssph-journal.org
9. Paz V, Dashti HS, Garfield V. “Is there an association between daytime napping, cognitive function, and brain volume? A Mendelian randomization study in the UK Biobank.” Sleep Health, 2023 (UK Biobank publication record). pubmed.ncbi.nlm.nih.gov
10. MedicalResearch.com. “Regular Napping Might Protect Against Some Aging Brain Shrinkage” (interview with Valentina Paz). July 2, 2023. medicalresearch.com
11. Leigh S. “Extended Napping in Seniors May Signal Dementia” (on Li P, Gao L, et al., Alzheimer’s & Dementia, 2022). UC San Francisco News, March 17, 2022. ucsf.edu
12. American Academy of Sleep Medicine. “Daytime sleepiness affects daily activities of most adults.” News release, November 17, 2025. aasm.org
13. MedlinePlus. “Sleep Disorders.” National Library of Medicine, last updated December 4, 2025. medlineplus.gov
14. American Academy of Sleep Medicine. “Dangers of Drowsy Driving.” Patient handout, 2012. aasm.org