The science of a good night’s sleep, and what actually helps
Most adults need at least seven hours. A steady schedule, morning light and a cool, dark room do more than most gadgets.
The short version
- Health bodies recommend at least seven hours of sleep a night for adults.
- Your internal body clock, the circadian rhythm, is set largely by light.
- A consistent wake-up time is one of the most effective habits.
- Caffeine works partly by blocking adenosine, a chemical linked to sleep pressure.
Sleep is not just rest. During sleep the brain consolidates memories, and the body carries out repair and regulation that affect mood, concentration and long-term health. This guide explains what is known about how sleep works and which everyday habits have good support. It is general information, not personal medical advice.
What happens while you sleep
Sleep is not one uniform state. Through the night, the brain moves through repeating cycles of different stages. Broadly, there is non-REM sleep, which ranges from light sleep to deep, slow-wave sleep, and REM sleep, named after the rapid eye movements that accompany it and often linked with vivid dreaming.
A full cycle typically lasts somewhere around 90 minutes, and most people pass through several cycles a night. Deep sleep tends to be more common earlier in the night, while REM periods tend to get longer towards the morning. That is one reason why cutting sleep short at the end of the night can affect how you feel during the day.
How much you need
Adults are generally advised to get at least seven hours of sleep a night, according to guidance from bodies such as the US Centers for Disease Control and Prevention. Teenagers and children need more; the CDC suggests eight to ten hours for teenagers and more again for younger children. Needs vary between individuals, but regularly getting much less is linked to a range of health problems.
Two systems that run your night
Two processes work together to decide when you feel sleepy.
Your body clock. Your circadian rhythm is an internal clock of roughly 24 hours that influences when you feel alert and sleepy. Light is its strongest signal. Bright light in the morning helps set it; bright light late in the evening, including from screens, can push it later. As darkness falls, the body releases more of the hormone melatonin, which helps signal that night has arrived.
Sleep pressure. The longer you are awake, the stronger the drive to sleep becomes. A chemical called adenosine builds up in the brain during waking hours and is linked with this growing pressure. Caffeine works partly by blocking adenosine’s effects, which is why it makes you feel more alert, and why a late coffee can make it harder to fall asleep.
When the body clock and sleep pressure line up, falling asleep is easier. Jet lag and shift work are difficult partly because they pull the two out of step.
Habits with good evidence
- Keep a consistent wake-up time, including at weekends where you can.
- Get daylight early in the day, ideally outdoors.
- Keep the bedroom cool, dark and quiet.
- Limit caffeine later in the day. Its effects can last for hours.
- Avoid heavy meals and alcohol close to bedtime. Alcohol may make you drowsy but tends to disrupt sleep later in the night.
- Wind down. A regular routine before bed signals that sleep is coming.
- Be active during the day. Regular physical activity is associated with better sleep, though vigorous exercise right before bed does not suit everyone.
- Keep naps short and early, if you nap at all, so they do not eat into night-time sleep pressure.
If you cannot get to sleep
Lying in bed for a long time feeling frustrated can make the bed itself feel like a place for worrying. Health services such as the NHS suggest that if you cannot sleep, you get up, do something calm in dim light, and go back to bed when you feel sleepy. Keeping a notepad by the bed to jot down tomorrow’s tasks can help some people stop going over them.
Common misconceptions
- “I can catch up at the weekend.” A long lie-in can reduce some short-term tiredness, but it also shifts your body clock, which can make Monday morning harder.
- “A nightcap helps me sleep.” Alcohol can speed up falling asleep but tends to fragment sleep later in the night.
- “Older people need much less sleep.” Sleep patterns change with age, and older adults may wake more often, but guidance for adults of all ages still points to around seven hours or more.
- “Snoring is always harmless.” Often it is, but loud snoring with pauses in breathing or gasping can be a sign of sleep apnoea and is worth mentioning to a doctor.
What is still uncertain
Scientists know a great deal about the effects of losing sleep, but some basic questions remain open. Researchers are still investigating exactly why we need sleep, what role dreaming plays, and how sleep interacts with long-term conditions such as heart disease and dementia. Much of the research on sleep and health is observational, which makes it hard to separate cause from effect. Sleep trackers can be useful for spotting patterns, but their estimates of sleep stages are approximate and should not be treated as a diagnosis.
When to get help
If you regularly struggle to fall or stay asleep, snore loudly, or feel very tired despite enough time in bed, talk to a doctor. Conditions such as insomnia and sleep apnoea are common and treatable. For long-term insomnia, a structured talking therapy known as cognitive behavioural therapy for insomnia, or CBT-I, is widely recommended, and a doctor can advise on whether it, or something else, is right for you.
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