Sleep is when the body does much of its maintenance. Tissues are repaired, memories are filed, and the hormones that control appetite, growth and stress are reset for the next day. Most adults need between seven and nine hours a night.
What happens during sleep
Sleep runs in cycles of roughly ninety minutes, moving between lighter sleep, deep sleep and dreaming sleep.
- Deep sleep dominates the first half of the night. Heart rate and breathing slow, and the body releases its largest pulses of growth and repair hormones.
- Dreaming sleep becomes longer towards morning and is linked to learning, memory and emotional processing.
Why deep sleep matters for repair
- Protein building in muscle and other tissues is supported by the hormones released in deep sleep.
- The immune system produces more of the signalling molecules it uses to coordinate its response.
- Energy stores in muscle and liver are refilled.
What short sleep does
- Appetite shifts. The hormones that signal hunger rise and those that signal fullness fall, so people tend to eat more.
- Blood sugar control weakens. Even a few nights of restricted sleep reduce how well the body handles glucose.
- Recovery slows. Physical performance, reaction time and tissue repair are all affected.
- Stress rises. Levels of the stress hormone cortisol stay higher into the evening.
Habits that support good sleep
- A regular bedtime and wake time, including weekends
- Daylight early in the day and dimmer light in the evening
- A cool, dark, quiet bedroom
- No caffeine late in the day
- Regular physical activity
This article is for general educational purposes only and is not medical advice.
Frequently asked questions
How much sleep do adults need?
Most adults need between seven and nine hours a night.
What is deep sleep?
The stage of sleep with the slowest brain activity. It dominates the first half of the night and is when much of the physical repair in the body takes place.
Why does poor sleep increase appetite?
Short sleep raises the hormones that signal hunger and lowers those that signal fullness.
Does sleep affect recovery from exercise?
Yes. Tissue repair, energy storage and performance all depend on adequate sleep.
Can you catch up on lost sleep?
Extra sleep helps, but it does not fully reverse the effects of regular short sleep. A consistent routine works better.
Is this medical advice?
No. This article is general educational information. Speak to a qualified healthcare professional about persistent sleep problems.