What this guide covers
Sleep is one of the basic habits of health, alongside diet, movement and medical care. The research is strong on some points and weaker on others. In each guide we separate what studies show from what they cannot show.
None of these pages gives a diagnosis. If you have symptoms, speak to a clinician. This page is general education and not medical advice. If you have ongoing sleep problems, loud snoring, breathing pauses or severe daytime sleepiness, speak to a doctor.
Body
Heart and metabolic health.
- Sleep, heart and metabolism What studies show and what they cannot prove.
- Sleep regularity and the heart Preliminary 2026 data in context.
- Earlier bedtime and weight A trial of short sleepers.
Mind
Mood, thinking and stress.
- Sleep and mental health A two way street.
- Sleep deprivation and brain fog Attention, memory and safety.
Life stages
Older adults and children.
- Sleep needs of older adults What changes with age.
- Child naps by age Why one schedule does not fit.
Food and supplements
What the evidence says.
- What to eat for better sleep Patterns, timing and caffeine.
- Magnesium and sleep Limited, low certainty evidence.
- Sleep supplements How to judge claims.
How to read health claims about sleep
- Observational studies show links, not proof of cause
- Randomised trials are stronger but shorter
- Preliminary conference abstracts are not peer reviewed
- News stories can simplify results
- Product claims are not evidence
When a headline says that sleep prevents a disease, ask what kind of study sits behind it. Our guides label evidence strength so you can judge for yourself.
Seven daily habits that support sleep and health
- Keep a regular wake time.
- Get daylight and move your body.
- Eat a balanced diet and finish large meals early.
- Limit caffeine after midday and keep alcohol modest.
- Manage stress with a calm evening routine.
- Keep the bedroom dark, cool and quiet.
- See a doctor about snoring, long term insomnia or low mood.
When sleep is a medical issue
Sleep problems sometimes have a medical cause. Sleep apnoea, restless legs, depression, thyroid problems, pain and some medicines can all disturb sleep. Treat these conditions with a professional. A calculator cannot do it, and neither can a supplement.
If you are unsure, take a two week sleep diary to your doctor. It speeds up the visit and gives you better answers.
Glossary of sleep health terms
- Association
- A link seen in data that does not prove cause.
- Randomised trial
- A study that assigns people by chance to different groups.
- Insomnia
- Trouble falling or staying asleep with daytime effects.
- Sleep apnoea
- Repeated pauses in breathing during sleep.
- CBT for insomnia
- A structured therapy that improves sleep habits and thoughts.
- Sleep restriction
- Cutting sleep below need, by choice or circumstance.
- Cardiometabolic
- Relating to the heart and to metabolism, including blood sugar.
Longer answers to common questions
Is long sleep unhealthy? Very long sleep is linked with illness in studies, but it may reflect health problems and not cause them. If you regularly need more than nine hours and still feel tired, see a doctor. Does a nap count? A nap adds to your total, but it is not a full substitute for night sleep.
Can I rely on a supplement? Evidence for most is limited. See our guides on magnesium and sleep supplements for how to judge claims.
How we judge health claims
For each health guide we looked first for systematic reviews, meta analyses and guidelines from medical societies, then for large cohort studies and randomised trials. We name the study and give a link so you can read it. Press coverage is used to find topics, not to prove claims.
If we could not open a source, we left out its numbers. If evidence is weak, such as for most supplements, we say that plainly. Your doctor knows your history, and we do not.
Where to start if you are overwhelmed
Pick one habit. For most people the best first step is a fixed wake time, followed by morning daylight. Once that feels easy, add a calm wind down hour and a caffeine cut off. Check progress after two weeks with the sleep debt calculator and the bedtime calculator.
Health is built from many small daily choices. Sleep is one that can be improved without cost, and it makes every other healthy habit easier.
Frequently Asked Questions
Does sleep affect health? ›
Studies link poor sleep with many risks, though cause is hard to prove.
How much sleep protects health? ›
7 to 9 hours for most adults.
Can food fix sleep? ›
Diet helps, but no single food is a cure.
Do supplements work? ›
Evidence is limited and varies by ingredient.
When to see a doctor? ›
For persistent insomnia, loud snoring or severe sleepiness.
Is this medical advice? ›
No.
Written by F.A and last updated on 5 November 2026. Claims are checked against the peer reviewed papers and public health sources listed below, and findings from small or early studies are labelled as such. We follow our editorial policy and explain how times and results are calculated in our methodology. Calculators run in your browser and store nothing. Found an error? Tell us and we will correct it.
Sources
- Hirshkowitz M et al. National Sleep Foundation's sleep time duration recommendations. Sleep Health 2015
- Watson NF et al. Recommended amount of sleep for a healthy adult. Sleep 2015
- Trauer JM et al. Cognitive behavioral therapy for chronic insomnia: a systematic review and meta analysis. Ann Intern Med 2015
This page gives general information for adults and is not medical advice. If you have ongoing sleep problems, loud snoring, breathing pauses or heavy daytime sleepiness, speak to a doctor. Times and results are estimates.