Understanding sleep

Senior Clinical Physiologist in Neurophysiology and Sleep at Bupa Cromwell Hospital
24 March 2016
A little girl asleep on her mum's shoulder

Sleep is an important part of our lives. Did you know that we spend around a third of our time sleeping? If you live to 90, the chances are you will have spent approximately 30 years entirely asleep.

Sleep is a temporary state in which you are unconscious, but from which you can be aroused (woken up).

For most people, a good night’s sleep is crucial for a refreshing and productive day.

So, why do I sleep?

Sleep is an essential part of our lives, but it’s not entirely clear why. There is still a lot of mystery surrounding the relationship between the brain and the process of sleeping.

What we do know is that sleep plays a vital role in:

  • ‘filing away’ memories in your brain
  • improving your ability to learn
  • regulating metabolism (the way your body breaks down food into energy)
  • reducing mental fatigue

How much sleep do I need?

People vary in how much sleep they need to stay healthy and feel well rested. It’s generally accepted that most adults will need between seven and nine hours daily.

Sleep patterns change throughout an individual’s life. A newborn baby sleeps on average 16–18 hours a day. By the time they turn five, they will sleep for approximately 10–12 hours. Babies’ sleep is polyphasic. This means they often need two or more sleeping periods (eg a night-time sleep and several daytime naps).

Older people need less sleep – as little as five or six hours – and often deep sleep disappears.

Phases of sleep

Sleep is divided into two main phases; each phase is divided into stages.

The first phase is called non-rapid eye movement sleep (NREM). This is how you spend most of your sleeping time. This phase has three different stages.

  • N1 corresponds with feeling drowsy.
  • N2 is a light stage of sleep, where you can easily be woken up. This is how you spend half of your sleep time.
  • N3 is a period of deep sleep.

The second phase is rapid eye movement sleep (REM), during which you tend to dream.

Sleep is a cyclical process. This means you have repeated cycles of NREM followed by REM. A cycle lasts on average 90 minutes and each cycle occurs four or five times a night, depending on how long you sleep for.

An image showing a person and a dog asleep

The sleep cycle

The human sleep-wake cycle is regulated by something called the circadian rhythm. Circadian rhythms are influenced by things like social and physical activity, and exposure to light and dark.

Adult humans are diurnal, which means we tend to have one period of sleep every 24 hours, usually lasting around seven hours. We sleep at night because the environment is quiet and because after a normal day, we feel tired in the evening and ready for sleep. If you’re feeling drowsy during the day after a normal sleep period, you’re probably not getting enough good sleep.

Many people try and fight daytime drowsiness by having a quick nap. For someone whose circadian rhythm is disrupted, napping can be an effective way of combating sleep deprivation. However, many people avoid napping during the day because they wake up feeling groggy or confused. If you find you need to nap a lot, this might indicate problems with your night-time sleeping. You might be waking up frequently during the night, which could indicate a condition like obstructive sleep apnoea (a breathing problem).

What happens if I don’t get enough sleep?

If you don’t get enough sleep, you may experience difficulties such as reduced alertness and concentration. Some studies have linked a lack of sleep with increased appetite and weight gain.  You’re also more susceptible to work accidents and it’ll take you longer to react when driving.

In the long term, sleep deprivation can have a big impact on your health. It may lead to an increase in hormones linked to stress; increase your risk of heart disease and high blood pressure; result in weight abnormalities; and even affect your immune system.

For our tips on how to get a good night’s sleep, read more on the Bupa Health Blog.




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Ana Noia
Senior Clinical Physiologist in Neurophysiology and Sleep at Bupa Cromwell Hospital

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