A good night’s sleep is just as important for your health as healthy eating and a daily exercise routine.  Like food and water, sleep is essential for survival, no wonder we spend about one-third of our lives sleeping.  The average adult needs 7-8 hours of sleep every night and less sleep on a regular basis can lead to health problems.

While sleep is important for mental and physical health, there are nevertheless still unanswered and intriguing questions about sleep, such as why we dream, or have sleep cycles.

What is sleep?

“Sleep is the natural state of rest in which your eyes are closed, your body is inactive, and your mind does not think” is the simple definition of sleep, provided by Collins Dictionary.

Behind the scenes, however, complicated chemical processes are taking place in the brain.  Neurotransmitters, nerve-signaling chemicals in the brain, act upon different groups of neurons (nerve cells) in the brain and, amongst other functions, control whether we are awake or asleep.  Neurotransmitters such as serotonin and norepinephrine keep some parts of the brain active while awake, while neurons at the base of the brain starts signaling when we fall asleep and appear to turn off those signals that keep us awake.

How much sleep do we need?

Why we need sleep:

We need sleep for many biological processes that are critical for our overall health.

The brain:  During sleep the brain stores new information, converts short-term memories into long-term memories, erases (forgets) unneeded information, and gets rid of waste in the form of toxic byproducts from the chemical processes taking place in brain cells.  These processes result in a refreshed, alert brain when we wake up in the mornings. 

Cellular restoration:  Sleep allows cells in the body to repair and regrow, allowing the body to restore itself.  For example, without sleep, neurons (nerve cells) may malfunction as they become depleted in energy and polluted with the byproducts of normal cellular activities.  Many cells in the body show increased production of proteins during sleep, with reduced breakdown of proteins. 

Energy conservation:  While sleeping, the body’s caloric intake for energy use is reduced, as the body then functions at a lower rate of metabolism.

Emotional well-being:  Brain activity in the areas that regulate emotion increases while sleeping, which supports emotional stability and healthy brain function.  Sleep deprivation can result in emotional overreaction and instability.  Chronic lack of sleep is a very powerful internal stressor for the body.

Weight maintenance:  Proper sleep plays a role in weight maintenance, as sleep controls hunger hormones by decreasing ghrelin (stimulates appetite) and elevating leptin (gives you feelings of satiety).  Lack of sleep can elevate ghrelin and suppress leptin, which results in experiencing hunger, eating more calories, and gaining weight.  Chronic lack of sleep has been linked to an increased risk of obesity, type 2 diabetes, and metabolic syndrome.

Insulin function:  Sleep may help to protect the cells in the body against insulin resistance, by keeping the cells healthy and balancing the release of insulin, a hormone that allows most cells to take up glucose (sugar) from the bloodstream for energy.  Insulin resistance occurs when the cells in the body do not respond properly to insulin, which can lead to high blood sugar levels and type 2 diabetes. 

Immune system:  Sleep is important for a healthy and strong immune system, as sleep deprivation can inhibit immune ability to fight invading microorganisms, such as bacteria, viruses, and germs.   While sleeping, the body makes immune cells, certain antibodies, and cytokines – which are proteins that help the body fight infection and inflammation.  When you are sick or highly stressed, sleep becomes even more important, as the body has a greater need for a healthy immune system.  When cytokines fight an infection, such as flu, it tends to make us sleepy, as the cytokines are sleep-inducing chemicals.

Heart health:  Sleep seems to support heart health, as chronic lack of sleep is associated with various risk factors for heart health, such as high blood pressure, insulin resistance, increased levels of inflammation, and elevated cortisol levels. 

Survival:  Animal studies have shown that sleep is necessary for survival, as laboratory rats that were deprived of any sleep only lived for about three weeks, instead of their normal life expectancy of two to three years.

Hormones:  Various hormones are released during sleep, such as melatonin that controls the sleep patterns, and growth hormone that helps the body to grow and repair itself.  The brain also releases the antidiuretic hormone arginine vasopressin (ADH) during sleep, which switches off the need to urinate often during the night.  ADH regulates and balances the amount of water in the blood by telling the kidneys how much water to conserve.  Cortisol is another hormone which levels decrease during the first hours of sleep and rises again soon after waking up.  Cortisol is known as the chronic stress hormone.  

Stages of sleep:

During sleep the body goes through multiple cycles of sleep for different lengths of time.  Each cycle lasts from 70 to 120 minute and repeats during sleep.  Each cycle goes through four stages of sleep – three stages of non-rapid eye movement and one stage of rapid eye movement (REM) sleep. 

Stage 1:  This stage occurs for about seven minutes while you drift in and out of sleep and brain waves, heart rate, muscle activity, and eye movement slow down during this stage.   During this stage many people experience sudden muscle contractions (jerks), often preceded by a sensation of starting to fall.

Stage 2:  This is the longest stage of sleep and consists of light sleep before you fall into deep sleep.  It is characterized by a decrease in body temperature, stopping of eye movements, relaxing of the heart rate and muscles in the body, while brain waves briefly spike before slowing down.

Stage 3:  This is the stage of restorative deep sleep when the eyes and muscles do not move, and brain waves slow down even more.  During stage 3 the body replenishes its energy and repair of cells, tissues, and muscles take place.  

Stage 4:  This stage happens after about 90 minutes of sleep and is characterized by REM sleep, where the eyes move rapidly from side to side.  The heart rate and blood pressure increase, breathing becomes more rapid, shallow, and irregular, while brain waves and eye movements increase.  Dreaming usually takes place during REM sleep and the brain processes information, in aid of memory and learning.

Sleep disorders:

Some people suffer from chronic long-term sleep disorders and the resulting sleep deprivation can interfere with daily life – in both work and social activities.  Lack of sleep is a powerful internal stressor for the body.

The most common sleep disorders are:

  • Insomnia: Short-term insomnia is a common occurrence that can result from incidences such as jet lag, diet, or stress.  Mild cases of insomnia can usually be cured by practicing good sleep habits.   Serious cases of insomnia would require medical intervention.  Insomnia tends to increase with age.
  • Sleep apnea: This condition is characterized by disrupted breathing while sleeping.  Usually sleep apnea results from fat buildup (being overweight) or loss of muscle tone due to aging, which allows the windpipe to collapse when muscles relax during sleep, blocking the air flow for 10 seconds or longer at a time and the person struggles to breathe.  Disrupted flow of oxygen to the brain can slightly wake the person to snort or gasp to open the windpipe again.  This cycle can repeat hundreds of times during the night.  The disrupted breathing is often associated with loud snoring – but is not the only cause of snoring.  Sleep apnea can also occur due to a malfunction of the neurons in the brain that control breathing during sleep, although it is a rare condition.
  • Restless legs syndrome:    This disorder causes unpleasant tingling, crawling, or prickling sensations in the legs and feet, resulting in an urge to move the legs for relief.  This constant leg movement can result in constant leg movements during the day and insomnia at night. 
  • Periodic limb movement:  This disorder causes repetitive jerking movements of the legs and can also occur in other limbs.  These jerking movements every 20 to 40 seconds can cause repeated awakening during the night and result in fragmented sleep.
  • Narcolepsy: This disorder is characterized by frequently falling asleep various times during the day.  These sleep attacks may last from several seconds to more than 30 minutes. 


While you were sleeping, the body and brain were very busy behind the scenes!  We all need a good night’s sleep to help our bodies recover from the day and to allow healing to take place.  Most adults need 7 to 9 hours of sleep every night to function well and to allow the body and brain time to repair, restore, and re-energize.  Sleep is also a powerful de-stressor for the body.  Sleeping well helps us to feel better physically and mentally, enabling us to perform optimally during the day, with a healthy positive outlook on life.


What is sleep and why is it important?  Published online.  American Sleep Foundation.  (www.sleepassociation.org)

10 Reasons why good sleep is important.  Published 24 February 2020.  Healthline.  (www.healthline.com)

What is the purpose of sleep?  Published 20 July 2020.  Healthline.  (www.healthline.com)

7 Amazing things that happen to your body while you sleep.  Published 14 March 2018.  Queensland health.  Queensland Government, Australia.  (www.health.qld.gov.au)


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