Sleep affects almost every system in your body, from the brain and heart to metabolism, immunity and mood. Long-term short or poor sleep is linked to a higher risk of high blood pressure, heart disease, diabetes, obesity and depression (NINDS).
Some effects are proven in experiments, such as slower thinking and reactions after short sleep. Others are associations from long-term studies. Those show that poor sleep and disease go together. They cannot always show which comes first. For most adults, the AASM and the Sleep Research Society recommend 7 or more hours a night (AASM).
This guide covers each body system at overview level and says how strong the evidence is. It also points you to our in-depth page on each topic.
What Does Your Body Do While You Sleep?
Sleep is not a switched-off state. Your body works to support healthy brain function and maintain your physical health. In children and teens, it also supports growth and development (NHLBI).
- Heart and blood vessels. In non-REM sleep, your blood pressure and heart rate fall. Your heart does not work as hard as when you are awake. In REM sleep and on waking, they rise back to normal waking levels (NHLBI).
- Brain. Without sleep, you cannot form or maintain the brain pathways that let you learn and create new memories. Sleep may also clear toxins that build up in the brain while you are awake (NINDS).
- Breathing and immunity. You breathe less often and less deeply during sleep. Parts of the immune system become more active at different times of day (NHLBI).
- Hormones. Deep sleep triggers the release of the hormone that promotes normal growth in children and teens. It also helps repair cells and tissues in adults (NHLBI).
Sleep And Your Health At A Glance
This table shows what poor or short sleep is linked to in each system. It also shows how firm each link is. Read “association” as “goes together with”, not “proven cause”.
| Body system | What poor sleep is linked to | Strength of evidence |
|---|---|---|
| Brain and memory | Trouble focusing, learning, remembering and reacting; slower reaction times and more mistakes | Strong for short-term effects on thinking. Links to dementia are associations, and the direction is not settled. |
| Mood and mental health | Depression, anxiety, irritability and poorer control of emotions | Strong two-way association. A large trial found treating insomnia reduced paranoia and hallucinations, which supports a causal role. |
| Heart and blood pressure | Coronary heart disease, high blood pressure and stroke | Consistent associations in long-term studies. Both short and long sleep predict heart outcomes, so cause is not proven. |
| Metabolism, weight and diabetes | Hunger hormone changes, weaker insulin response, obesity and type 2 diabetes | Short-term studies show hormone and insulin changes; long-term studies show associations with diabetes and obesity. |
| Immune system | More colds and trouble fighting common infections | Moderate. People who slept less than 6 hours were more likely to catch a cold after controlled virus exposure. |
| Inflammation | Higher levels of inflammation markers such as CRP and IL-6 | Mixed. Linked to sleep disturbance in cohort studies, but pooled sleep-deprivation experiments did not show the same rise. |
| Pain | New and worsening chronic pain | Moderate. Sleep problems predict later pain more reliably than pain predicts sleep problems. |
| Gut | Changes in gut bacteria; more sleep problems in people with IBS | Early. Mostly observational and animal research. |
| Hormones | Disrupted timing of cortisol, growth hormone and appetite hormones | Well established for daily hormone rhythms; long-term health effects are less clear. |
| Longevity | Higher risk of death with both short and long sleep | Association only. Long sleep is more likely to reflect illness than to cause it. |
Sources: NHLBI, NINDS, AASM, and the PubMed reviews cited in each section below.
Brain And Memory
This is where the evidence is clearest. Sleep helps with learning and forming long-term memories. Too little quality sleep makes it harder to focus and think clearly (NHLBI).
People who are sleep deficient take longer to finish tasks. They react more slowly and make more mistakes. After several nights of losing even 1 to 2 hours of sleep, your ability to function suffers as if you had not slept at all for a day or two (NHLBI).
Lack of sleep can also cause microsleep. These are brief moments of sleep while you are awake, and you may not notice them. Driver sleepiness is estimated to be a factor in about 100,000 car accidents and about 1,500 deaths each year (NHLBI).
Over the long term, poor sleep and Alzheimer’s disease seem to affect each other. The disease can disturb sleep. Poor sleep may add to the build-up of beta-amyloid, a protein that clumps in the brain in Alzheimer’s (Sleep Foundation).
Sleep problems are common in people with Alzheimer’s and Parkinson’s disease. It is still an open question whether lack of sleep leads to these disorders or the diseases cause the lack of sleep (NINDS).
Missing sleep night after night? The sleep deprivation guide covers the signs, the short-term effects and how to recover.
Mood And Mental Health
Sleep deficiency changes activity in the parts of the brain that control emotions and behavior. It has been linked to depression, suicide and risk-taking behavior (NHLBI). The link runs both ways. Sleep problems can worsen mental health conditions, and mental health problems can lead to poor sleep (Sleep Foundation).
The best evidence that sleep can drive mental health comes from treatment trials. In a randomized trial of 3,755 university students with insomnia, digital CBT for insomnia reduced insomnia. It also reduced paranoia and hallucinations compared with usual care (Freeman and colleagues, 2017).
For depression, anxiety, bipolar disorder, PTSD and ADHD one by one, see our hub on sleep and mental health. For day-to-day mood, irritability and emotional control, read how sleep affects your emotions.
Heart And Blood Pressure
People who do not sleep enough, or who wake often at night, may have a higher risk of coronary heart disease, high blood pressure, obesity and stroke (NHLBI). One reason may be the nightly dip. Blood pressure drops during normal sleep, and sleep deprivation prevents this drop (Sleep Foundation).
A meta-analysis of 15 long-term studies with about 475,000 people looked at sleep length. Short sleep was associated with a greater risk of developing or dying of coronary heart disease and stroke.
Long sleep was also associated with higher risk. The authors called sleep duration a predictor, or marker, of heart outcomes rather than a proven cause (Cappuccio and colleagues, 2011).
NHLBI-funded research also found that untreated sleep disorders raise the risk of heart problems (NHLBI).
If you snore loudly or stop breathing in your sleep, sleep apnea may be part of the picture. Our page on sleep apnea health risks explains the links. The sleep apnea guide covers symptoms and diagnosis.
Metabolism
The way your body handles fat follows circadian clocks in the liver, fat and muscle. So it may handle fat differently if you eat at unusual times (NHLBI).
Studies show that too little quality sleep can lead to a weaker response to insulin. It can also lead to eating more food, especially fatty, sweet and salty foods, less physical activity and metabolic syndrome (NHLBI).
Weight And Diabetes
Weight. When you do not get enough sleep, your level of ghrelin goes up. This is the hormone that makes you feel hungry. Your level of leptin, which makes you feel full, goes down. So you feel hungrier than when you are well rested (NHLBI).
Sleep loss is one of the risk factors for obesity. Sleep loss in children raises their risk of becoming overweight (Sleep Foundation). NHLBI-funded research found that adults who regularly sleep 7 to 8 hours a night have a lower risk of obesity and high blood pressure (NHLBI).
Diabetes. Sleep deficiency results in higher-than-normal blood sugar, which may raise your risk of diabetes (NHLBI). A meta-analysis of 10 long-term studies with about 108,000 people looked at four sleep problems. Short sleep (5 to 6 hours or less), long sleep, trouble falling asleep and trouble staying asleep each predicted a higher risk of type 2 diabetes (Cappuccio and colleagues, 2010).
Sleep apnea is also a risk factor for type 2 diabetes. It has been shown to increase insulin resistance (Sleep Foundation).
Immune System
Ongoing sleep deficiency can change how your body’s natural defense against germs responds. You may have trouble fighting common infections (NHLBI).
In one study, 164 healthy adults wore wrist monitors for a week to measure their sleep. Then they were given a cold virus. Those who slept less than 5 hours, or 5 to 6 hours, were more likely to develop a cold than those who slept more than 7 hours (Prather and colleagues, 2015).
For vaccines, the immune cells involved and what the research does not show, read can good sleep improve your immune system.
Inflammation
This link is real but less tidy than many headlines suggest. A meta-analysis of 72 studies with more than 50,000 people found that sleep disturbance was associated with higher levels of the inflammation markers CRP and IL-6. So was very long sleep. Pooled experimental sleep-deprivation studies did not show a rise in these markers (Irwin and colleagues, 2016).
So poor sleep and inflammation go together. How much one causes the other is still being worked out. Our page on poor sleep and inflammation breaks down the studies.
Pain
Sleep and pain seem to affect each other. Emerging evidence suggests the effect of sleep on pain may be stronger than the effect of pain on sleep (Sleep Foundation).
A review of prospective and experimental research found that sleep problems reliably predict new and worsening chronic pain. They are a stronger predictor of pain than pain is of sleep problems (Finan and colleagues, 2013). See does lack of sleep make pain worse for the experiments and what helps.
Gut
Research on sleep and the gut is young. A 2020 review found that short sleep and broken sleep are associated with an imbalance in gut bacteria. The link seems to run in a cycle, because gut bacteria also influence sleep (Matenchuk and colleagues, 2020).
Much of this work is in animals or small groups, so it is too early for firm advice. Reflux, IBS, meal timing and probiotics are covered in the gut-brain connection.
Hormones
Your body makes different hormones at different times of day. These follow your sleep pattern and circadian clocks. In the morning it releases hormones such as cortisol that help you wake up. In children, the hormones that trigger puberty are released in pulses at night (NHLBI).
Sleep also plays a role in puberty and fertility (NHLBI). Appetite hormones are covered under weight above.
Hormone shifts can also disturb sleep. If you are going through menopause, our menopausal sleep quality calculator helps you track how your nights are changing.
Longevity
Sleep deficiency is linked to many chronic health problems and even a greater likelihood of death (NHLBI). A meta-analysis of 16 studies with about 1.4 million people found that both short and long sleep were associated with a higher risk of death over 4 to 25 years (Cappuccio and colleagues, 2010).
The long-sleep finding needs care. The AASM consensus panel said long sleep is more likely to reflect chronic illness than to cause it (AASM).
Chronically sleep-deprived people are also more likely to have certain types of cancer (NINDS). Our page on sleep and cancer risk explains what the evidence does and does not show.
Curious how your own habits add up? The chronic sleep deprivation risk calculator looks at your usual sleep and flags patterns worth acting on.
Association Or Cause: How To Read Sleep And Health Studies
Most long-term evidence on sleep and disease is observational. It shows that people who sleep poorly are more likely to develop a condition. But the condition itself may explain part of the link. So may a third factor, such as stress, shift work or another illness.
The stronger evidence comes from experiments that change sleep on purpose. Examples are the cold-virus study, sleep restriction studies on appetite and blood sugar, and treatment trials such as CBT for insomnia.
When experiments and population studies point the same way, you can be more confident that sleep matters. They do for thinking, mood and appetite.
How To Protect Your Health With Sleep
- Aim for 7 or more hours. The AASM and Sleep Research Society found 6 or fewer hours inadequate to sustain health and safety (AASM). Check your own target in how much sleep do you need.
- Think beyond hours. Healthy sleep also needs the right timing, daily regularity, good quality and no sleep disorders (AASM).
- Keep a schedule. Go to bed and wake up at the same time each day (NINDS).
- Move during the day. Exercise for at least 30 minutes most days, but not within a few hours of bedtime (NINDS).
- Watch caffeine, nicotine and alcohol. Avoid caffeine and nicotine late in the day, and alcohol before bed (NINDS).
- Make the bedroom for sleep. Avoid bright lights and loud sounds. Keep the room a comfortable temperature, and keep screens out (NINDS).
- Do not lie in bed awake. If you cannot sleep, do something relaxing, such as reading, until you feel tired (NINDS).
When To See A Doctor
- You have problems sleeping or feel unusually tired during the day. Most sleep disorders can be treated effectively (NINDS).
- You often feel you could doze off while reading, watching TV, sitting in traffic or riding in a car (NHLBI).
- Someone notices you snore loudly or stop breathing in your sleep. Or you have high blood pressure or diabetes alongside poor sleep.
- Trouble sleeping lasts for weeks. CBT for insomnia is usually recommended as the first treatment for long-term insomnia (NHLBI). See our insomnia guide.
An estimated 50 to 70 million Americans have chronic sleep disorders (NHLBI), so you are far from alone.
Sleep And Health FAQs
How Does Sleep Affect Your Health?
Sleep supports the brain, heart, metabolism, immune system, hormones and mood. Long-term short or poor sleep is linked to higher risk of heart disease, diabetes, obesity and depression.
Why Is Sleep Important For Health?
During sleep your body repairs itself, sets hormone rhythms, lowers blood pressure and helps the brain store memories. Missing it affects how you think, feel and react the next day.
What Happens To Your Body When You Do Not Sleep Enough?
In the short term, attention, memory, reaction time and mood suffer, and hunger hormones shift. Over months and years, the risk of several chronic diseases rises.
Does Poor Sleep Cause Disease, Or Is It Just Linked?
Both, depending on the system. Effects on thinking and appetite are shown in experiments. Most links to heart disease, dementia and lifespan are associations.
How Much Sleep Do Adults Need For Good Health?
The AASM and Sleep Research Society recommend 7 or more hours a night for healthy adults, with regular timing and good quality.
Can You Make Up For Lost Sleep At The Weekend?
Not fully. Depending on how sleep deprived you are, sleeping longer at weekends may not be enough to replace the sleep you missed.