2010Sleep
Cappuccio et al.
16 studies, 1.38 million people
Short sleepers (under 6 hours) had 12% higher risk of death; long sleepers (over 9 hours) had 30% higher, often because long sleep signals illness.
Find on PubMed ↗Research library · Recovery & repair
Sleep: when your body repairs
Sleep is when your brain clears waste, your memories get filed, your muscles rebuild and your hormones reset. How regularly you sleep turns out to matter as much as how long.
Good evidenceUpdated Oct 2026 · 4 new studies+12%risk of death sleeping under 6 hours a nightCappuccio 2010, Sleep, 1.3M+ people
−20–48%death risk for the most regular sleepers vs the leastWindred 2024, Sleep, 60,977 people
4.2×more likely to catch a cold when sleeping under 6 hoursPrather 2015, Sleep, 164 adults
01
The basics
What happens while you sleep
A night's sleep runs in cycles of about 90 minutes, usually 4–6 a night. Each cycle moves from light sleep into deep sleep and then REM (dream) sleep. Deep sleep is concentrated early in the night; REM sleep gets longer towards morning.
In deep sleep, growth hormone peaks, tissues repair and the brain's 'glymphatic' system flushes out waste proteins, including the amyloid linked to Alzheimer's. In REM sleep, the brain processes emotions and strengthens learning.
Your body clock (circadian rhythm) times all of this. It's set mainly by light hitting your eyes in the morning. Going to bed and waking at different times every day confuses it, a bit like constant jet lag.
A typical night's sleep
Deep sleep comes mostly in the first half of the night. REM (dream) sleep gets longer towards morning.
02
How it works
What short sleep does to your body
1
Too little or irregular sleep
Fewer deep and REM cycles, and a body clock out of sync.
2
Blood sugar
Insulin works worse the next day; hunger hormones rise and cravings follow.
3
Immunity
Fewer immune cells respond, so infections take hold more easily.
4
Brain
Less waste clearance, worse memory, focus and mood.
03
Measure it
How to check your sleep
- Duration: time actually asleep, not time in bed. Wearables give a fair estimate; a simple diary works too.
- Regularity: how much your bedtime and wake time vary across the week, including weekends. Aim for less than 30–60 minutes of difference.
- How you feel: needing an alarm every day, dozing off in the afternoon or relying on caffeine are signs you're short.
- Warning signs: loud snoring, gasping or pauses in breathing can mean sleep apnea. Ask your doctor about a sleep test.
Try your number
Very shortShortA bit shortHealthyLong
410
Adults need 7–9 hours (7–8 over 65). Regularly sleeping 9+ hours can be a sign of illness worth checking.
04
What the research says
The key studies
2024Sleep
Windred et al.
60,977 UK Biobank adults
The most regular sleepers had 20–48% lower risk of death than the least regular. Regularity predicted death better than sleep length.
Find on PubMed ↗2013Science
Xie et al.
Mice
During sleep, the space between brain cells grew by about 60%, letting fluid wash out waste proteins much faster than when awake.
Find on PubMed ↗1999Lancet
Spiegel et al.
11 young men
After six nights of 4 hours' sleep, healthy young men handled sugar like people on the way to diabetes. It reversed with recovery sleep.
Find on PubMed ↗2015Sleep
Prather et al.
164 adults given a cold virus
People who slept under 6 hours were 4.2 times more likely to catch the cold than those sleeping over 7.
Find on PubMed ↗2003Sleep
Van Dongen et al.
48 adults
Two weeks of 6 hours a night impaired attention as much as one to two nights of no sleep at all, yet people felt only slightly sleepy.
Find on PubMed ↗05
New in 2025–26
What the newest research adds
The newest evidence shows that talking therapy for insomnia (CBT-I) works even for people with long-term illness, and that the timing and rhythm of sleep, not just hours, is linked to many diseases. Simple exercise like yoga, tai chi and walking may also help poor sleepers.
The new studies, in order
Every study added to this page since January 2025. Green rings are the strongest evidence: large trials or meta-analyses.
CBT-I: insomnia gone in half of people
Scott et al., 2025, 67 trials, 5,232 people with long-term illness and insomnia. Share whose insomnia went into remission.
NewSep 2025JAMA Intern Med
Scott et al.
67 trials, 5,232 people with chronic diseases
CBT-I, a structured talking therapy, put 54% of people with insomnia into remission versus 18% of controls. It worked in people with cancer, pain, heart and other long-term conditions.
Strong evidenceRead the source ↗
NewJan 2025Health Data Science
Wang et al.
88,461 UK Biobank adults with wrist trackers, 6.8 years
Measured sleep traits were linked to 172 diseases, 42 of them with at least double the risk. Falling asleep after 00:30 was tied to 2.57 times the risk of liver cirrhosis, and almost half the links involved sleep rhythm rather than sleep length.
Good evidenceRead the source ↗
NewJul 2025BMJ Evid Based Med
Bu et al.
22 trials, 1,348 people with insomnia
Yoga may add nearly 2 hours of total sleep and tai chi more than 50 minutes, while walking or jogging cut insomnia severity by nearly 10 points. Two in three trials had design flaws, so this is promising rather than proven.
Early evidenceRead the source ↗
NewDec 2025SLEEP Advances
McAuliffe et al.
US county data, 2019 to 2025
Across US counties, getting less than 7 hours of sleep was more strongly tied to shorter life expectancy than diet, exercise or loneliness. Only smoking mattered more. This is a population-level link, not proof of cause.
Early evidenceRead the source ↗
What this changes for you
If you have insomnia, ask for CBT-I (talking therapy for insomnia) before sleeping pills; it works even alongside long-term illness and there are good apps and online courses. Keep a regular schedule and try to be asleep before about 00:30.
06
Take action
How to sleep better
Start with the body clock: fixed wake time and morning light are the strongest levers.
- 1
Same wake time every day
Including weekends. Your bedtime will follow.
- 2
Morning light
10–30 minutes outside within an hour of waking, even on cloudy days.
- 3
Caffeine cut-off
None after early afternoon. Caffeine 6 hours before bed cut sleep by over an hour in one study (Drake 2013).
- 4
Cool, dark, quiet
Around 18 °C, blackout curtains or an eye mask, earplugs if needed.
- 5
Wind down
Dim lights and put screens away 30–60 minutes before bed. Keep work out of the bedroom.
- 6
Alcohol early or not at all
It helps you fall asleep but breaks up sleep and cuts REM later in the night.
- 7
Insomnia? Try CBT-I
Cognitive behavioural therapy for insomnia is the first-choice treatment, ahead of sleeping pills.
07
Myth or fact
Common myths, checked
✕ MythI can catch up at weekends.
✓ FactLie-ins help a little, but shifting your sleep times creates 'social jet lag' that has its own costs.
✕ MythA nightcap helps me sleep.
✓ FactAlcohol knocks you out but fragments sleep and suppresses REM.
✕ MythOlder people need less sleep.
✓ FactNeeds drop only slightly. Older adults still need about 7–8 hours, though sleep gets lighter.
✕ MythI'm fine on 5 hours.
✓ FactIn studies, people who were short of sleep felt fine while their performance kept getting worse.
08
Questions
Frequently asked
Are naps good or bad?
A 10–20 minute nap before 3 pm can help. Long or late naps make night sleep harder.
Should I use melatonin?
It helps with jet lag and shift work. For everyday insomnia, habits and CBT-I work better.
What about sleep trackers?
Good for duration and regularity; less accurate for sleep stages. Don't let the score stress you out.
09
Test yourself
True, partly true or myth?
Read each claim and pick an answer: the card flips to show the verdict and why. Not sure? Use “Just reveal”.
Card № 01True or myth?
Most adults need 7–9 hours of sleep a night.
True
Most adults need 7–9 hours of sleep a night.
That's the consensus of the American Academy of Sleep Medicine and Sleep Research Society. Very few people truly thrive on under 6.
Card № 02True or myth?
You can fully catch up on lost sleep at the weekend.
Myth
You can fully catch up on lost sleep at the weekend.
Lie-ins help a little, but studies show weekday sleep loss still harms blood sugar control and alertness.
Card № 03True or myth?
Keeping a regular wake-up time matters as much as total hours.
True
Keeping a regular wake-up time matters as much as total hours.
UK Biobank studies (2023–24) found sleep regularity predicted death risk even more strongly than sleep duration.
Card № 04True or myth?
Alcohol helps you sleep.
Partly true
Alcohol helps you sleep.
It helps you fall asleep faster, but breaks up the second half of the night and cuts REM sleep.
Card № 05True or myth?
During deep sleep the brain clears waste products faster.
True
During deep sleep the brain clears waste products faster.
Animal studies of the glymphatic system show waste clearance rises in sleep; human work points the same way.
Card № 06True or myth?
Older people need less sleep.
Myth
Older people need less sleep.
Older adults often sleep less well, but their need stays at about 7–8 hours.
Card № 07True or myth?
Loud snoring with gasping or pauses can be a sign of sleep apnoea.
True
Loud snoring with gasping or pauses can be a sign of sleep apnoea.
It's very common, often undiagnosed and linked to high blood pressure, heart disease and daytime sleepiness. It's treatable.
Card № 08True or myth?
CBT for insomnia works better long-term than sleeping pills.
True
CBT for insomnia works better long-term than sleeping pills.
Guidelines recommend CBT-I as first treatment; its benefits last after treatment ends.
Card № 09True or myth?
Screens before bed ruin sleep because of blue light.
Partly true
Screens before bed ruin sleep because of blue light.
Light matters a bit, but what you're doing (scrolling, stress, staying up later) seems to matter more.
Card № 10True or myth?
If you can't sleep, staying in bed and trying harder is best.
Myth
If you can't sleep, staying in bed and trying harder is best.
If you're awake more than about 20 minutes, get up, do something calm in dim light and return when sleepy.
Nothing here yet. Try another filter.
10
Sources
References and related topics
- Cappuccio et al. (2010). Sleep. 16 studies, 1.38 million people. PubMed ↗
- Windred et al. (2024). Sleep. 60,977 UK Biobank adults. PubMed ↗
- Xie et al. (2013). Science. Mice. PubMed ↗
- Spiegel et al. (1999). Lancet. 11 young men. PubMed ↗
- Prather et al. (2015). Sleep. 164 adults given a cold virus. PubMed ↗
- Van Dongen et al. (2003). Sleep. 48 adults. PubMed ↗
- Scott et al. (2025). JAMA Intern Med. 67 trials, 5,232 people with chronic diseases. Source ↗
- Wang et al. (2025). Health Data Science. 88,461 UK Biobank adults with wrist trackers, 6.8 years. Source ↗
- Bu et al. (2025). BMJ Evid Based Med. 22 trials, 1,348 people with insomnia. Source ↗
- McAuliffe et al. (2025). SLEEP Advances. US county data, 2019 to 2025. Source ↗