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Science of sleep

Sleep is important for our physical, emotional and mental wellbeing.

In hours of darkness our brain produces a hormone called melatonin. This is the hormone which we need in order to feel tired. Daylight stops our body’s production of melatonin and therefore we wake up for the day.

How do sleep cycles work?

There are 4 sleep stages. 1 is called rapid eye movement (REM) sleep and 3 are different parts of non-REM (NREM) sleep.

  • Sleep stage N1 is a light sleep where we are easily disturbed.
  • Sleep stage N2 is a deeper sleep which we should spend half the night in.
  • Sleep stage N3 is our deepest sleep which happens more in the first third of the night. N3 sleep is important for growth and repair. Our body releases growth hormone and repairs the body from the day’s activities.
  • After stages N1, N2 and N3 we then go into REM sleep. This is where we dream. Dreaming is important for our learning because this is when all the day’s events are processed and stored into our short and long term memory.

All of the sleep stages make up a sleep cycle.

Diagram of the sleep cycle going through stages of awake, REM and deep sleep stages

We usually have 4 to 5 sleep cycles per night through all of these different sleep stages.

When we transition from one sleep cycle to another it is normal to have ‘partial awakenings’ every 90 minutes or so.

During a partial awakening, we can be awake for up to 2 minutes at a time without knowing we are awake. If everything is the same as when we fell asleep, we will go back to sleep without remembering that we’ve woken up.

If a parent or carer is present at bedtime and is no longer there during the partial awakening, your child will wake up and look for their parent or carer to help them to resettle. This is the most common reason for children waking up in the night and is easily solved by helping them to settle without a parent or carer present at bedtime.

If something has changed, for example a door opened or light been turned off and so on, then we could wake fully and struggle to resettle. It is important that the settings at bedtime remain consistent throughout the night.

How long should my child sleep for?

The amount of sleep required changes with age. Shown here are some average sleep times for different ages. However, be mindful that these are just averages and many children and young people will differ from these averages.

  • Toddles (1 to 2 years) need around 11 to 14 hours of sleep.
  • Pre-schoolers (2 to 3 years) need around 10 to 13 hours of sleep.
  • School age (6 to 13 years) need around 9 to 10 hours of sleep.
  • Teenagers (14 to 17 years) need around 8 to 10 hours of sleep.
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Please note: this is a generic information sheet relating to care at Sheffield Children’s NHS FT. These details may not reflect treatment at other hospitals. This information is not intended as a substitute for professional medical care. Always follow your healthcare professionals’ instructions. If this resource relates to medicines, please read it alongside the medicine manufacturer’s patient information leaflet. If this information has been translated into another language from English, efforts have been made to maintain accuracy, but there may still be some translation errors. If you are unsure about any of the guidance in this resource or have specific questions about how it relates to your child, always ask your healthcare professional for further advice.

Resource number: SLP14

Resource Type: Article

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