Why We Sleep

Sleep is not wasted time

Every night you spend hours lying still with your eyes closed, doing — it seems — nothing at all. But sleep is one of the most important and busy times of your whole day. While you rest, your body and brain are hard at work behind the scenes, fixing, growing and organising. We spend about a third of our lives asleep, and for very good reasons.

Imagine trying to run a tablet or phone that never gets charged. Soon it slows down and stops. Your body is similar: sleep is how it recharges, repairs and gets ready for another day. Let's discover what really happens while you sleep, and why it matters so much.

What happens to your body while you sleep

When you sleep, your body slows down on the outside but speeds up its repair work on the inside.

• Healing and repair. Your body mends tiny bits of damage from the day and fights off germs. This is why you need extra sleep when you are poorly — your body is busy getting you better. Sleep helps your immune system fight infection.
• Growing. Children grow most while they sleep. Your body releases a special growth hormone mostly at night, which is one reason children need more sleep than grown-ups.
• Resting the heart and muscles. Your heartbeat and breathing slow down, giving your muscles and heart a gentle break to recover and get stronger.

So sleep is not lazy time at all. It is your body's nightly repair and growing shift, working alongside all the systems of the human body.

What happens in your brain while you sleep

Your brain might be even busier than your body during sleep. One of its biggest night jobs is sorting memories. During the day you take in huge amounts of information. At night, your brain reviews it, keeps the important bits, and files them away so you can remember them later. This is why a good night's sleep helps you learn — students who sleep well after studying remember more.

Your brain also tidies itself up, clearing away waste that built up during the day. A rested brain can concentrate, solve problems and stay in a good mood. A tired brain finds it hard to focus, gets grumpy, and makes more mistakes. Have you ever felt cross or muddled after a poor night's sleep? That is your tired brain asking for rest.

Sleep cycles and dreams

Sleep is not one long, flat blank. It happens in repeating cycles, each lasting about an hour and a half, and you go through several each night. Within each cycle there are different stages:

• Light sleep, as you first drift off and your body relaxes.
• Deep sleep, when your body does most of its healing and growing. It is hard to wake someone from deep sleep.
• REM sleep, which stands for rapid eye movement. In this stage your brain becomes very active and your eyes flicker about under your eyelids. This is when most dreams happen.

Nobody is completely sure why we dream. Many scientists think dreams happen while the brain works through memories and feelings. Some dreams are happy, some are strange, and most are forgotten by the time you wake up.

How much sleep do you need?

Different ages need different amounts of sleep, and children need more than adults because they are still growing and their brains are developing fast.

Age group	Sleep needed each night
Toddlers (1–2 years)	11–14 hours
Young children (3–5 years)	10–13 hours
School children (6–12 years)	9–11 hours
Adults	7–9 hours

If you wake up tired, struggle to concentrate, or feel grumpy, your body may be asking for more sleep.

How to sleep well

You can help yourself get good sleep with a few simple habits:

• Keep a regular bedtime. Going to bed and waking at similar times sets your body clock, the internal timer that makes you sleepy at night.
• Wind down calmly. A quiet routine — a wash, pyjamas, a story — tells your brain it is time to rest.
• Turn off screens early. The bright light from tablets and phones can trick your brain into thinking it is daytime, making it harder to fall asleep.
• Make your room dark and cool. Darkness helps your body make a sleep chemical called melatonin.
• Avoid sugary or fizzy drinks at night, as they can keep you awake.

Try it: keep a sleep diary

Find out how sleep changes the way you feel.

1. For one week, write down what time you went to bed and what time you woke up each day. Work out how many hours you slept.
2. Each morning, give yourself a score out of 5 for how you feel: 5 means wide awake and cheerful, 1 means tired and grumpy.
3. Also note how easy it felt to concentrate at school that day.
4. At the end of the week, look at your diary. Do you notice a pattern between more sleep and better days?

Why it works: A sleep diary turns you into a scientist studying your own body. Most people find that on nights with more sleep, they feel happier, think more clearly and learn more easily the next day. Seeing your own results is powerful proof that sleep really does help your body and brain — and a good reason to protect your bedtime.