How much sleep do I really need?
Seven to eight hours per night is the best-supported target range for adults. If you are consistently sleeping fewer than 7 hours, getting more sleep is not a luxury but a serious investment in your health.
Seven to eight hours per night is the sweet spot for most adults. An analysis of 36 systematic reviews, covering more than 4.4 million participants from 30 countries, found this range to be most favourably associated with health. That held true for both younger adults and older adults alike: there was no clear difference by age.
Fewer than 7 hours structurally increases the risk of overweight, diabetes, high blood pressure, heart disease, stroke and mental health problems. A large study of more than 320,000 people in Asia, followed for an average of 14 years, found that the risk of death was lowest at exactly 7 hours and rose with both shorter and longer sleep. That J-shape matters: too little is harmful, but so is a great deal.
Consistently sleeping more than 10 hours was associated in that same study with a 34% higher risk of death in men and 48% in women, compared with 7 hours. Whether long sleep is itself the cause, or whether it more often occurs in people who are already ill, the study could not determine. Take it as a signal, therefore, not as proof that sleeping long kills you.
Sleep duration matters for your brain as well. In older adults, the risk of mild memory decline was lowest at around 7 hours per night. Those who slept fewer than 6 hours had a 22% higher risk of such decline; those who slept more than 8 hours had a notably higher risk of as much as 78%. This is observational research in Chinese older adults and not proof of causation, but the U-shaped pattern aligns with the other findings.
Two practical points: a short afternoon nap of fewer than 30 minutes was associated with a 27% lower risk of memory decline in older adults. And if you exercise intensely in the evening, try to finish at least 4 hours before bedtime. People who exercised vigorously closer to bedtime fell asleep later, slept for a shorter time and had a higher heart rate during the night.
The core findings come from a broad umbrella review (33054337), two large cohort studies (34477853, 26890214), a cross-sectional study in older adults (39223492) and an observational study using exercise data (40234380). All associations are correlational; randomised controlled trials on sleep duration are not feasible at this scale for practical reasons. In the exercise study, two authors are affiliated with the company that supplied the measurement equipment.
How much does a consistent sleep schedule actually matter?
A consistent sleep schedule genuinely matters. Irregular sleep times are strongly associated with more depression, anxiety, a higher BMI and even higher mortality, independent of how many hours you sleep. The evidence is predominantly associative, but consistent enough for clear advice: go to bed and wake up at fixed times every day, including on weekends.
How much melatonin should you take to sleep better?
For most adults, 4 mg appears to have the greatest effect, but it should be taken 2 to 3 hours before bedtime; if you are older than 55, the extended-release formulation (2 mg) is the only one officially recommended.
What can I do to sleep better?
CBT-I is the most powerful approach for persistent sleep problems; if you do not have access to it, ask your general practitioner about a shorter behavioural treatment of four sessions. Fixed sleep times, less caffeine and alcohol in the evening, and regular exercise are the best-supported self-help steps.
Does getting more sleep improve my memory?
Sufficient sleep demonstrably benefits your memory: your brain processes and stores new information while you sleep. Too little sleep impairs that processing after just one night.
What is the difference between REM sleep and deep sleep, and do I need both?
You need both sleep stages: deep sleep and REM sleep each do something different for your memory and brain, and getting a full night's sleep is the most concrete way to obtain enough of both.
What is sleep debt and can you actually pay it back?
Paying off sleep debt over a weekend does not work: after two recovery nights, cognitive functions are still impaired. Consistently sleeping more over several weeks is the only evidence-based approach.