Understanding sleep

Ana Noia
Senior Clinical Physiologist in Neurophysiology and Sleep at Cromwell Hospital
13 March 2018

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This article is more than three years old. It reflects the best available evidence at the time of publication.

Did you know that we spend around a third of our time sleeping? If you live to 90, the chances are you’ll have spent approximately 30 years entirely asleep. It’s clear that sleep is an essential part of our lives. But understanding sleep and its benefits isn’t quite so straightforward.

So, why do I sleep?

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

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

Based on what scientists understand about sleep, the main theories are that it is for:

  • ‘filing away’ memories in your brain
  • regulating metabolism and replenishing your energy stores
  • reducing mental fatigue

How much sleep do I need?

It’s hard to give a definitive answer to this. 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 in a 24-hour period.

Sleep patterns change throughout an individual’s life. A newborn baby sleeps on average around 16 hours a day. By the time they turn five, they’ll 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 don’t sleep deeply.

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: the above sequence occurs repeatedly throughout the night. A cycle lasts on average 90 minutes and each cycle occurs four or five times a night, depending on how long you sleep for.

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 what you consider 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 has been disrupted, napping can be an effective way of combating the effects of 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.

If you’re looking to get better or more sleep, it may help to understand sleep hygiene. Look at our information on getting a good night’s sleep.

Are you interested in learning more about your health? Discover more about our range of health assessments.

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

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