How much sleep you need.
Most adults do best on seven hours or more, and the times you sleep matter almost as much as the hours.
How much is enough
Sleep specialists in the United States agree that adults should sleep seven hours or more on a regular basis, and that sleeping less than that, night after night, is linked to poorer health (Watson, 2015). The National Sleep Foundation's panel puts it at seven to nine hours for adults and seven to eight for older adults, and says need varies from one person to the next (Hirshkowitz, 2015).
More than nine hours can be right for young adults, after a run of short nights, or when you are ill. For everyone else it is not known whether that much carries a risk.
Why regular times matter
When you sleep matters as well as how long. In a UK study that followed about 61,000 adults wearing a wrist sensor, people with the most regular sleep and wake times had a 20 to 48% lower risk of dying during the study than the least regular, and regularity predicted it better than hours did (Windred, 2024).
That is an association in a mostly older group, not proof that regular times cause better health. Still, going to bed and getting up at similar times every day, weekends included, costs nothing.
Sleep, muscle and fat loss
Short sleep makes a fat-loss phase harder. In a small trial, adults on the same reduced-calorie diet for two weeks lost 55% less fat, and more lean mass, with 5.5 hours in bed than with 8.5, and were hungrier (Nedeltcheva, 2010). In an eight-week trial, about an hour less sleep on five nights a week gave the same weight loss but less of it from fat, and weekend catch-up sleep did not fully make up for it (Wang, 2018).
In the gym, six hours or less lowered performance, strength included, by about 8% on average across 69 studies, most of them in men (Craven, 2022). One night with no sleep at all lowered muscle protein building by 18% the next day in a small study (Lamon, 2021). These studies are small or short, so read them as a direction rather than a rule: sleep is part of the plan, not a break from it.
Keeping track in Perdura
Rest › Check-in takes last night's hours in one tap, and Rest › Trends shows your nights over the weeks you choose. Perdura shows what you logged and never sets a sleep target for you.
If you often sleep badly for weeks, or feel sleepy in the day despite enough time in bed, talk to a doctor. Long-lasting insomnia has treatments that work, with cognitive behavioural therapy for insomnia the one with the strongest evidence (Edinger, 2021).
Log last night's sleep in two taps and see your nights add up. Free, no card.
Sources
- Watson NF et al. Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society. Sleep. 2015;38(6):843-4.
- Hirshkowitz M et al. National Sleep Foundation's sleep time duration recommendations: methodology and results summary. Sleep Health. 2015;1(1):40-43.
- Windred DP et al. Sleep regularity is a stronger predictor of mortality risk than sleep duration: A prospective cohort study. Sleep. 2024;47(1).
- Nedeltcheva AV et al. Insufficient sleep undermines dietary efforts to reduce adiposity. Ann Intern Med. 2010;153(7):435-41.
- Wang X et al. Influence of sleep restriction on weight loss outcomes associated with caloric restriction. Sleep. 2018;41(5).
- Lamon S et al. The effect of acute sleep deprivation on skeletal muscle protein synthesis and the hormonal environment. Physiol Rep. 2021;9(1):e14660.
- Craven J et al. Effects of Acute Sleep Loss on Physical Performance: A Systematic and Meta-Analytical Review. Sports Med. 2022;52(11):2669-2690.
- Edinger JD et al. Behavioral and psychological treatments for chronic insomnia disorder in adults: an American Academy of Sleep Medicine clinical practice guideline. J Clin Sleep Med. 2021;17(2):255-262.
General information based on the studies above, not medical advice. If sleep, tiredness or your health worries you, talk to a doctor.