The short answer
Enough sleep clearly helps attention, learning and memory, and lab trials show that cutting sleep raises appetite, blood pressure and blood sugar and weakens the response to vaccines. Large studies link regular short sleep with heart disease, type 2 diabetes, colds, depression and dementia, though they can't fully prove cause and effect.
On this page
How strong is the evidence for each benefit?
We grade each claim on studies in people, using the four grades explained here. The grade says how sure we can be, not how big the effect is.
| Benefit | Grade | Why |
|---|---|---|
| Memory, attention and learning | Strong | Many controlled lab trials show that cutting sleep impairs attention, reaction time and learning, and that sleep after learning helps memories stick. |
| Mood and mental health | Moderate | Insomnia roughly doubles the later risk of depression, and a trial of 3,755 students found treating insomnia also eased paranoia, low mood and anxiety. |
| Immune system and infections | Moderate | People who slept under 6 hours were about four times as likely to catch a cold after being given the virus, and short sleep weakened responses to vaccines. |
| Weight and appetite | Moderate | Lab trials show short sleep raises hunger hormones and makes people eat about 385 more calories a day. Long-term weight effects come from observational studies. |
| Heart and blood pressure | Moderate | Studies of nearly half a million people link short sleep with more heart disease and stroke. Lab trials show sleep loss raises stress hormones and the nerve activity that drives blood pressure. |
| Type 2 diabetes | Moderate | Short and broken sleep predicted type 2 diabetes in studies of over 100,000 people, and restricting sleep worsens blood sugar control in lab trials. |
| Dementia | Weak | Short sleep in mid-life was linked with more dementia 25 years later in one large British study. Cause and effect are unclear. |
Why is “short sleep is bad” easier to prove than “more sleep is good”?
Nobody can randomly assign thousands of people to sleep 5 or 8 hours a night for twenty years, so long-term evidence comes from studies that follow people and compare them. Those studies keep finding the same thing: people who regularly sleep less than about 6 hours, and those who sleep 9 or more, do worse on average than people who sleep 7 to 8 hours.
The trouble is that poor sleep is tangled up with many other things: shift work, stress, low income, pain, depression, smoking and drinking. Researchers adjust for these, but they can’t adjust for everything. And illness can cause bad sleep rather than the other way round. That’s especially true for long sleep, which is often a sign of being unwell.
To get closer to cause and effect, we also look at:
- Lab trials that cut healthy volunteers’ sleep for a few nights or weeks. These show clear, quick changes in attention, appetite hormones, blood sugar control, blood pressure and immune responses.
- Treatment trials that improve people’s sleep and see what else improves. The best example is the OASIS trial, where treating insomnia improved mental health.
When all three kinds of evidence point the same way, we grade a claim higher.
How much does sleep affect lifespan?
A review of 16 studies following more than 1.3 million people for 4 to 25 years found that short sleepers were 12% more likely to die during follow-up than people sleeping 7 to 8 hours, and long sleepers 30% more likely. That is a real but modest difference, smaller than the effect of smoking or inactivity. The short-sleep link is the more likely one to be partly causal.
Does it matter how you get to 7 hours?
Yes. Regular timing, enough time in bed and treating sleep problems such as insomnia and sleep apnoea all matter. Sleeping pills lengthen sleep a little but there’s no evidence they bring the health benefits of natural sleep, and they carry risks of their own. See how to sleep better.
In this section
- Sleep and your heart: blood pressure, heart disease and stroke
How short sleep is linked with high blood pressure, heart disease and stroke, how strong the evidence is, and why sleep apnoea matters for the heart.
Moderate - Does lack of sleep make you gain weight? Sleep, hunger and appetite
How short sleep changes the hormones that control hunger, how many extra calories tired people eat, and whether sleeping more helps weight loss.
Moderate - Sleep and your immune system: colds, infections and vaccines
How short sleep affects your chance of catching a cold, how well vaccines work, and inflammation in the body, from virus-exposure and vaccine trials.
Moderate - Sleep, memory and concentration: what the research shows
How lack of sleep affects attention, reaction time and memory, why sleep after learning helps memories stick, and what that means for students and drivers.
Strong - Sleep and mental health: depression, anxiety and mood
How poor sleep is linked with depression and anxiety, and what a trial of nearly 4,000 UK students found about treating insomnia to help mental health.
Moderate - Sleep and type 2 diabetes: how short sleep affects blood sugar
How short and broken sleep are linked with type 2 diabetes, what lab trials show about blood sugar control after sleep loss, and why sleep apnoea matters.
Moderate - Does poor sleep raise the risk of dementia?
What studies show about sleep and dementia, including the Whitehall II study of British civil servants, the brain's cleaning system and what is unknown.
Weak
Common questions
What are the benefits of getting enough sleep?
The best-proven benefits are for the brain: better attention, reaction times, learning and memory. There is also good evidence that enough sleep helps keep appetite, blood sugar, blood pressure and mood in check and helps the immune system respond to infections and vaccines.
Does lack of sleep shorten your life?
People who regularly sleep under about 6 hours die earlier on average in large studies, by a modest amount. Some of that is because illness and stress cause poor sleep, but lab trials show sleep loss has harmful effects of its own, so it is probably partly cause and effect.
Can one bad night harm your health?
No. A single bad night makes you tired, less alert and more irritable the next day, but the health risks in studies come from short sleep night after night for years.
References
- Cappuccio FP et al. Sleep duration and all-cause mortality: a systematic review and meta-analysis of prospective studies. Sleep, 2010.pubmed.ncbi.nlm.nih.gov
- Cappuccio FP et al. Sleep duration predicts cardiovascular outcomes: a systematic review and meta-analysis. European Heart Journal, 2011.pubmed.ncbi.nlm.nih.gov
- Van Dongen HP et al. The cumulative cost of additional wakefulness. Sleep, 2003.pubmed.ncbi.nlm.nih.gov
- Prather AA et al. Behaviorally assessed sleep and susceptibility to the common cold. Sleep, 2015.pubmed.ncbi.nlm.nih.gov
- Freeman D et al. The effects of improving sleep on mental health (OASIS): a randomised controlled trial. Lancet Psychiatry, 2017.pubmed.ncbi.nlm.nih.gov
- Al Khatib HK et al. The effects of partial sleep deprivation on energy balance: a systematic review and meta-analysis. European Journal of Clinical Nutrition, 2017.pubmed.ncbi.nlm.nih.gov
First published 4 November 2026. Spotted an error? Tell us and we'll correct it. Read our editorial policy.