In this article
Sleep takes up about a third of our lives. Research keeps showing how much the body and brain accomplish while we are unconscious, and how much we lose when we cut it short.
Key facts
- 7 hours or more: the minimum recommended for adults aged 18 to 60 by the American Academy of Sleep Medicine.
- 30.5% of US adults slept less than seven hours on average in 2024, according to the CDC.
- 4 to 6 cycles of light, deep and REM sleep make up a typical night.
- Short sleep is linked to higher risks of obesity, diabetes, high blood pressure, heart disease and depression.
The stages of sleep
A night’s sleep moves through repeating cycles of about 90 minutes. Each cycle includes lighter sleep, deep sleep and rapid eye movement (REM) sleep, when most vivid dreaming happens. Deep sleep is more common early in the night; REM sleep lengthens toward morning.
| Stage | What happens | Why it matters |
|---|---|---|
| Light sleep | Heart rate and breathing slow; body temperature drops | Transition into deeper sleep |
| Deep sleep | Brain waves slow; hardest to wake | Physical repair, growth hormone release, immune function |
| REM sleep | Brain is very active; muscles relax; vivid dreams | Memory, learning and emotional processing |
What sleep does
For the brain
During sleep the brain consolidates what you learned during the day, strengthening important memories. Studies consistently find that people remember new information better after a night’s sleep. Sleep also appears to help clear waste products that build up in the brain while we are awake.
For the body
Deep sleep supports tissue repair and the immune system. Sleep also helps regulate hormones that control appetite, which is one reason short sleep is linked to weight gain.
For mood
Even one bad night makes people more irritable and less able to handle stress. Long-term sleep problems are closely linked with anxiety and depression, in both directions.
How much sleep do you need?
| Age | Recommended sleep per 24 hours |
|---|---|
| Teenagers (13 to 18) | 8 to 10 hours |
| Adults (18 to 60) | 7 hours or more |
| Adults (61 to 64) | 7 to 9 hours |
| Adults (65 and older) | 7 to 8 hours |
Despite that advice, the US Centers for Disease Control and Prevention found that 30.5 percent of adults slept less than seven hours on average in 2024. The American Academy of Sleep Medicine warns that regularly sleeping less than seven hours is associated with obesity, diabetes, high blood pressure, heart disease, stroke and frequent mental distress.
Habits that help
- Keep a regular schedule, going to bed and getting up at similar times, even at weekends.
- Get daylight in the morning, which helps set your body clock.
- Limit caffeine after lunchtime; its effects can last six hours or more.
- Keep the bedroom dark, quiet and cool.
- Put screens away before bed, both for the light and the mental stimulation.
- Avoid heavy meals and alcohol late at night; alcohol may help you fall asleep but disrupts sleep later.
A Sensible Guide to Reading Nutrition Labels
What you eat also affects how you feel and sleep; our guide to reading nutrition labels can help with choices during the day.
Sleep across a lifetime
Sleep needs change with age. Babies sleep most of the day. Teenagers need eight to ten hours, but their body clocks shift later, which makes early school starts difficult. Adults need at least seven hours. Older adults often sleep more lightly and wake more often, although their overall need does not fall much.
Shift workers face special challenges because their sleep runs against their body clock. Keeping the bedroom completely dark, protecting sleep time and keeping days off as regular as possible can help.
Frequently asked questions
Can I catch up on sleep at the weekend?
Extra sleep can reduce some short-term effects of a bad week, but it does not fully reverse the effects of regular short sleep. A consistent schedule works better.
Are naps good or bad?
A short nap of 20 to 30 minutes early in the afternoon can improve alertness. Long or late naps can make it harder to sleep at night.
When should I see a doctor about sleep?
If you regularly struggle to fall or stay asleep, snore loudly with pauses in breathing, or feel very sleepy during the day despite enough time in bed, speak to a doctor. Conditions such as sleep apnea and insomnia are common and treatable.
Health note: this article is general information and not a substitute for advice from a doctor or other qualified health professional.
