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The science of sleep The science
of sleep

You may only need a few hours sleep every night to feel refreshed - or you may hit the snooze button until the last possible moment. But why do we have to sleep, and how much do we really need?

 

The time that you fall asleep is controlled by your internal body clock, also called your circadian rhythm. It's triggered by your eye absorbing less light as it gets dark each evening. This sends messages to your brain causing the hormone melatonin to be produced. Melatonin plays a role in making you feel drowsy and getting you ready for sleep.

Despite this, no one knows exactly why we sleep. However, scientists think it might give our brains time to rest.

Sleep is controlled by your body clock, also called your circadian rhythm

What happens when we sleep?

When you are asleep, your brain cycles between Rapid Eye Movement (REM) and non-REM sleep, and you go through about five cycles of sleep every night. Each complete cycle of non-REM and REM sleep lasts between 90 and 110 minutes.

Non-REM
During non-REM sleep your brain is inactive, but your body may still move around. There are four stages to non-REM sleep.

  • Drowsiness - the muscles relax, your heart rate decreases and your body temperature lowers.
  • Light sleep - you are unconscious and unaware of your surroundings; you are sleeping lightly but can still be roused.
  • Slow wave sleep - your blood pressure gradually falls, you may talk or walk in your sleep.
  • Deep slow wave sleep - it is difficult to be woken during this stage and you feel confused if you are.

As you get older, slow wave sleep becomes less frequent and less deep. This means you wake up more easily.

REM sleep
During REM sleep the brain is active, but the body muscles are completely relaxed. However, your eyes move rapidly from side to side. REM sleep takes up about a fifth of your sleep. This is when you dream.

The occasional sleepless night doesn't cause too many problems, but can make you feel tired and forgetful

Sleepless nights?

The occasional sleepless night doesn't cause too many problems, but can make you feel tired and forgetful. Over longer periods, lack of sleep will also affect your decision making, your reactions and your judgement. It may even be a factor in the development of obesity, high blood pressure, diabetes and mental health problems. The effects of sleep deprivation have led scientists to believe that a good night's sleep is essential for day-to-day functioning.

How much is too much?

On average we spend a third of our lives asleep. Exactly how much sleep you need varies between different people, and partly depends on your age. Children and babies need much more sleep than adults - babies sleep about 17 hours a day. Most adults need about seven to eight hours sleep each night. As you get older you need the same amount of sleep, but tend to wake up more easily.

The quality of sleep you have also influences how rested you feel. Recent Swiss research suggests that the ability to sleep soundly may run in families.

  • Publication date: September 2008