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Is 6 Hours of Sleep Enough? What Research Says (and 5 or 7)

For most adults, no. Two weeks of 6-hour nights impaired thinking while sleepiness ratings barely rose. What the research says about 5, 6 and 7 hours.

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Is 6 Hours of Sleep Enough? What Research Says (and 5 or 7)

Is 6 hours of sleep enough? For most adults, no. Sleep experts recommend 7 or more hours a night on a regular basis, and 6 hours sits below the recommended range in every adult guideline. One short night is not the same as six hours most nights. In a lab study, two weeks of 6 hours or less in bed impaired people's thinking as much as up to two nights with no sleep at all, while their sleepiness ratings barely rose after the first days.

Recommended sleep for adults, from the main guidelines:

AgeRecommended sleep per 24 hours
18 to 607 hours or more
61 to 647 to 9 hours
65 and over7 to 8 hours

Sources: American Academy of Sleep Medicine (AASM) and Sleep Research Society, National Sleep Foundation, as tabled by the CDC. The NHS says adults need 7 to 9 hours on average.

How much sleep do adults need?

Most adults need at least 7 hours. In 2015 the AASM and the Sleep Research Society asked 15 sleep experts to review 5,314 articles on sleep length and health, then make a recommendation for adults aged 18 to 60. They concluded that "adults should sleep 7 or more hours per night on a regular basis to promote optimal health."

The National Sleep Foundation's panel landed in the same place the same year: 7 to 9 hours for adults and 7 to 8 for older adults. The NHS uses 7 to 9 hours for adults on average, and says "you probably do not get enough sleep if you're constantly tired during the day."

Sleep need does vary. The National Sleep Foundation panel said sleep outside the range may be appropriate for some people, "but deviating far from the normal range is rare." Six hours is below the bottom of every recommended range, so for most people it means running short.

What happens when you sleep 6 hours a night?

A 2003 University of Pennsylvania study put this to a controlled lab test. Researchers gave healthy adults aged 21 to 38 either 4, 6 or 8 hours in bed a night for 14 days, under lab supervision. A separate group went 3 nights with no sleep. Forty-eight people took part across both experiments.

In the 6-hour and 4-hour groups the deficits were cumulative, growing across the 14 days on all the tasks measured. The authors concluded that 6 hours or less a night had impaired performance as much as up to 2 nights of total sleep deprivation. The "up to" matters: the 4-hour group did worse than the 6-hour group, and the study's summary doesn't say how much of that figure belongs to 6 hours alone. This was also 6 hours in bed, so time asleep was probably a little less.

The long-term picture comes from consensus statements and population studies. They show links, not proof.

  • The AASM statement says sleeping under 7 hours a night on a regular basis is associated with weight gain and obesity, diabetes, high blood pressure, heart disease and stroke, depression and a higher risk of death, as well as weaker immune function, more errors and more accidents.
  • A 2010 meta-analysis of 16 studies covering about 1.38 million people found short sleepers had a 12% higher risk of death over the follow-up period. Long sleepers had a 30% higher risk. Sleep was reported by questionnaire, and the summary doesn't define short sleep in hours, so this is not a 6-hour figure.
  • The "seven hours" finding for survival comes from a 2002 American Cancer Society study of more than 1.1 million adults, followed up to 1988. The best survival was at 7 hours a night. People reporting 6 hours or less, and those reporting 8 or more, had a higher risk of death. The authors concluded that short sleep seemed to carry little risk distinct from existing health conditions, and that "causality is unproven."

Can you function on 6 hours of sleep?

You can get through the day on 6 hours, and after the first few days you may not feel much worse. Tests say you're slower than you think.

That gap is the key result from the 2003 study. People's ratings of their own sleepiness rose at first and then barely moved, even as their test scores kept falling. The authors read the ratings as showing that participants "were largely unaware of these increasing cognitive deficits." Feeling fine on 6 hours is not good evidence that you are fine.

A second study, from the Walter Reed Army Institute of Research, gave 66 volunteers 3, 5, 7 or 9 hours in bed for a week. In the 5- and 7-hour groups, reaction speed on an attention test dropped and then levelled off at a lower point. The authors say the brain adapts, but performance settles at a reduced level.

It matters most behind the wheel. An AAA Foundation analysis of US police-reported crashes compared the sleep of drivers who contributed to a crash with that of drivers who did not. Against drivers who had slept 7 hours or more in the previous 24 hours, the estimated crash rates were:

  • 6 to 7 hours of sleep: 1.3 times
  • 5 to 6 hours: 1.9 times
  • 4 to 5 hours: 4.3 times

The 6 to 7 hour figure is the smallest and least certain. It was only just statistically significant (95% confidence range 1.1 to 1.7), and it was not significant in some of the report's cross-checks. Drivers who usually slept 6 to 7 hours showed no statistically significant rise. Sleeping 1 to 2 hours less than your usual amount came with 1.3 times the crash rate, also only just significant (range 1.0 to 1.7). Sleep was self-reported.

Why do I feel better on 6 hours than 8?

One possible reason is how you wake up, not how long you slept. Grogginess right after waking is called sleep inertia. A review of the research found it is worse after abrupt waking from deep sleep than from lighter sleep, and it can happen after a normal 8-hour night. Prior sleep loss usually makes it worse, because it increases deep sleep. Without major sleep loss, it rarely lasts more than 30 minutes.

So how groggy you feel at 7am is a poor guide to how much sleep you need. If you want to time your alarm around sleep cycles, the sleep cycle calculator works out bedtimes for you.

Irregular timing can shift things too. In a 2019 lab study, people's body clocks were delayed once short nights resumed after a catch-up weekend, and the NHS advises sticking to your regular hours after a bad night. If you regularly need far more than 9 hours, raise it with a GP, because habitually long sleep can be a sign of a health problem.

Is 6 hours enough for one night?

In the 2003 study the losses built up night after night, so a single 6-hour night is a smaller problem than a run of them. It still has costs. In the AAA data, drivers who had slept 6 to 7 hours in the past 24 hours had a higher crash rate (see above), and a 2022 meta-analysis linked sleep loss of 6 hours or less to lower exercise performance. Take more care if you drive. Keep your normal wake time the next morning rather than sleeping in, and go to bed at your usual time. Our same-day plan for recovering from a bad night covers the rest of the day.

A short nap in the early afternoon can help, although the NHS advises people with insomnia not to nap during the day. A review of napping research, whose authors urge caution about its conclusions, found naps "can reduce sleepiness and improve cognitive performance," and 5 to 15 minute naps helped almost at once, for 1 to 3 hours. NSDR (non-sleep deep rest) is an option when you can't nap. NSDR keeps you awake, so it is unlikely to leave you groggy the way waking from deep sleep can. In a 2026 trial of 60 active young adults, a 25-minute nap raised readiness to perform where 10 minutes of NSDR had no significant effect. So if you have the time, nap. NSDR does not replace sleep. More in NSDR vs napping and how to nap without feeling groggy.

What about 5 or 7 hours?

Is 5 hours of sleep enough?

No, not for nearly anyone. Five hours is well below every adult recommendation. In the 2003 study, the 4-hour group did worse than the 6-hour group, so less sleep brought bigger losses. In the AAA crash data, drivers who usually slept 4 to 5 hours a day had 5.4 times the crash rate of those who usually slept 7 or more, although that estimate is imprecise (range 1.6 to 17.6) because few drivers were in the group.

Is 7 hours of sleep enough?

Yes, for most adults. Seven hours meets the AASM recommendation and is the bottom of the National Sleep Foundation and NHS ranges, so between 6 and 7, aim for 7. One catch is that 7 hours in bed is not 7 hours asleep. In the Walter Reed study, even the group with 7 hours in bed showed a drop in reaction speed that levelled off rather than recovering. If you fall asleep slowly or wake in the night, give yourself a bit more than 7 hours in bed.

Are some people fine on 6 hours?

A few people may be. A 2009 study in Science found a variant of the DEC2 gene in people who naturally sleep short, and mice given the same mutation slept less. A 2019 study found a rare variant of the ADRB1 gene in people "who require fewer hours of sleep than most."

Sleeping 6 hours may often mean running short rather than being a short sleeper. In a small 2005 study of 17 young adults, those who usually slept less fell asleep faster in daytime tests and slept longer when given up to 16 hours a day in bed. The authors concluded that people who habitually sleep less "carry a higher sleep debt," and that differences in sleep duration "may primarily reflect" self-selected sleep restriction.

How to get from 6 to 7 hours

Aim for an extra half hour first, then another. Five steps:

  1. Fix your wake time. Get up at the same time every day, as the NHS advises, weekends included.
  2. Move bedtime 30 minutes earlier. Give it a week or two, then add another 30 minutes if you need it.
  3. Set a caffeine cut-off. The NHS advises no tea or coffee, and no alcohol, in the 6 hours before bed.
  4. Wind down for an hour. The NHS suggests relaxing for at least an hour before bed, with a bath or a book, and keeping phones and TV out of the last stretch.
  5. Get light in the morning. In a study of 109 office workers, more circadian-effective light (light that registers with the body clock) in the morning went with falling asleep faster at night, especially in winter. Sleep was self-reported.

For more detail, see our 7-step sleep schedule reset and habits for sleeping better.

When to see a GP

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See a GP if:

  • you're often sleepy in the day even after 7 hours or more in bed
  • you snore loudly, or someone has seen your breathing stop and start or heard you gasp or choke in your sleep (possible signs of sleep apnoea)
  • you've had trouble sleeping for 3 months or longer, on at least several nights a week
  • changing your sleeping habits hasn't helped
  • you feel sleepy when you drive. The NHS says not to drive when you feel sleepy.

For ongoing sleep problems, CBT-I (cognitive behavioural therapy for insomnia) is the recommended first treatment. Ask your GP.

This is general information, not medical advice. NSDR is not a treatment for any condition.

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FAQ

Is 6 hours of sleep enough if I nap?

A nap can help on the day, but it is no reason to settle for 6 hours a night. The napping research looks at how a nap affects the hours that follow, not whether it makes up for weeks of short nights. Naps can reduce sleepiness, and short ones of 5 to 15 minutes helped for 1 to 3 hours in the research. Keep them short and in the early afternoon, the time the review found works best.

Is 6 hours of sleep enough for the gym?

Acute sleep loss can cost you some performance in the gym. A 2022 meta-analysis of 69 studies, where most participants were men, counted 6 hours or less in 24 hours as sleep loss and found exercise performance about 7.6% lower on average, with large differences between studies. The average mixes missed nights with shorter ones, so it may overstate what a plain 6-hour night costs, and it says little about months of 6-hour nights. The clearest drops came after a missed night or an unusually early alarm. Morning sessions were largely unaffected, so after a short night, train earlier in the day if you can.

Can you catch up on sleep at the weekend?

Sleeping in at the weekend pays back some sleep, but it doesn't fully undo the week. In a small 2019 lab study of young, healthy adults on 5-hour nights, those who slept as long as they liked at the weekend got about 1.1 hours of extra sleep in total. When the short nights started again, their insulin sensitivity fell by 9 to 27% compared with baseline. The authors suggested weekend recovery sleep "is not an effective strategy" against those metabolic effects. In the Walter Reed study, reaction speed in the 5- and 7-hour groups was still lower after 3 nights of 8 hours in bed.

Sources