Sleep and the importance of

When you sleep, your body rests, conserving energy and decreasing blood pressure, heart rate, breathing and body temperature. At the same time, your brain remains active, laying down memory, restoring daytime mental functioning and carrying out processes that lead to physical growth.

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There are 5 stages of sleep, progressing from light sleep through to rapid eye movement (REM) sleep. The stages are described and characterised as follows:

Stage 1– light sleep

• Transition between sleep and waking.
• Person is easily roused.
• Fleeting thoughts.
• Eyes move slowly.
• Reduced muscle activity. 

Stage 2

• Eye movements stop.
• Brief dreams.

Stage 3 – deep sleep

• Body temperature falls .
• Person is hard to awaken. 

Stage 4 – deep sleep

• Body temperature falls further. 
• Brain’s use of energy decreases. 
• Muscle tone decreases slightly. 
• Person may sleepwalk. 

Stage 5 – Rapid eye movement (REM)

• Eyes move rapidly to and fro. 
• Most dreams occur.
• Heart rate and blood pressure increase. 
• Limb muscles are paralysed. 
• Brain is very active and uses a lot of energy.

REM sleep happens about every 90 minutes during the night, and REM periods lengthen as the night progresses, while the time spent in non-REM stages 3 and 4 decreases.

Over a typical night, you spend about 20% of the time in REM sleep and 80% of the time in non-REM sleep. However, these proportions vary throughout life. Babies spend at least half of the time they’re asleep in REM sleep, but this proportion decreases as children mature, and from late childhood onwards only 20% of the night is spent in REM sleep.

Sleep is thought to play an important role in the following processes:

• controlling your body temperature and energy use (metabolism)
• keeping your immune system working
• controlling your brain functioning and restoring your memory
• keeping your heart and blood vessels healthy
• repairing tissues and stimulating growth in children (growth hormone released during sleep is responsible for both)
• regulating your appetite and weight and controlling your blood glucose levels.

If you aren’t getting enough sleep on a regular basis, these processes are interrupted and your risk of developing long-term health problems increases.

How much sleep you need changes during your lifetime, with babies needing a lot more than adults. Teenagers needs lots of sleep, women's sleep patterns change throughout their lives and older adults sleep less soundly. Sleep needs also vary between people.

Read more about how much sleep is recommended by stage of life.

Mood and concentration problems

Lack of sleep can make you grumpy, impatient and less tolerant. It can make you feel more stressed out and less able to cope with things. Sleep is linked to your mental health – if you’re not getting enough sleep, you’re more likely to feel depressed and anxious.

Lack of sleep also makes it difficult to make decisions and remember things. This can affect your productivity at work, ability to drive or carry out other tasks. 

Hunger and weight gain

If you haven’t had enough sleep, you might find yourself hungrier than usual. This is your body’s way of finding energy. You’ll often crave unhealthy food that is high in fat and sugar, so you might find your waistline expanding due to the increase in calories. Also, a lack of energy makes it harder to exercise during the day, therefore leading to weight gain.

Looking tired

Dark circles under your eyes, and your skin looking dull and unhealthy can be signs you are not getting enough sleep. When you sleep, your body repairs damaged cells so not enough sleep can really show on your face.

Lower libido

When you’re tired, your libido can suffer. The last thing you feel like doing is expending energy and working up a sweat. Lack of sleep lowers your testosterone, a hormone that plays a key role in a person’s sex drive. 

Sleepy during the day

If you aren’t getting enough sleep at night, you’re more likely to feel sleepy the next day. You may feel especially tired in the afternoon and have trouble staying awake. 

Getting sick more often

If you find yourself getting sick often, it could be due to a lack of sleep. When you’re tired and your body is run down, your immune system is weakened, therefore increasing your chance of catching colds and other ailments.

Read also about sleep deprivation and parenting.

If you regularly aren’t getting enough sleep, your sleep loss adds up. The total sleep lost is called your sleep debt. For example, if you lose 2 hours of sleep each night, you'll have a sleep debt of 14 hours after a week.

The harm caused by not getting enough sleep can be immediate, such as in having an accident due to not being able to focus and respond quickly. Other effects can take years to develop, such as an increased risk of developing a chronic health problem.

Lack of good sleep can lead to:

• excessive daytime sleepiness, tiredness and lethargy
• morning headaches
• poor memory and difficulty focusing
• anxiety and depression
• chronic health problems such as obesity, diabetes and cardiovascular disease
• an increased risk of alcohol and drug dependence
• having a car accident
• making mistakes at work, including causing accidents
• relationship problems
• lack of sex drive. 

In young people, lack of quality sleep may have a direct effect on their health, development, behaviour and ability to socialise and get along with their peers.

Getting enough sleep can be likened to banking your savings. If you take sleep out of your account, you have to put it back in to restore the balance – there’s no other way to catch up. To restore your sleep balance, you need at least 2 nights in a row of unrestricted good quality sleep.

See sleep tips for ideas on how to improve your chances of a good night’s sleep. Read more about sleep with our Te Kete Haerenga sleep resource and see how well you are doing with improving your sleep habits with our sleep tips tracker. [PDF, 136 KB]

If you’re having ongoing sleep issues, or you still feel unwell despite getting enough sleep, please consult your healthcare provider as there may be other causes.