Why Do We Sleep and Why We Need It

Sleep, like breathing, is something we all do without thinking about it. But why do we sleep, and what happens when we don’t get enough of it? Sleep holds several essential benefits for the body and mind. Many people suffer from not getting enough sleep and struggle to get a good night’s sleep. To understand how to get better sleep, we need to understand the science of why we do it in the first place. The purpose of this guide is to explain what sleep is and why it’s so important for our overall health.

We’ll look at sleep and it’s purpose first to better understand it’s importance.

The science behind sleep

What happens if we don't sleep
Did you know you need 7-9 hours of shut-eye to function at your best, but are you getting it?

Humans beings spend 1/3, or 33% of their life sleeping. It seems odd to some, going into a state of hibernation, where we become less responsive to outside stimuli. Sleep makes us vulnerable, however, there must be a good reason that our mind and body has these temporary shutdowns.

The act of sleeping regenerates our mind and body. Without sleep, our bodies and minds start to fail. While lack of sleep in itself can’t kill a person, the effects of sleep deprivation can indirectly lead to death. Numerous studies and research have been done over the years on sleep, it’s effects on the human brain and body, and how to improve it.

Purpose of sleep

Sleep has several essential purposes for both the mind and body. The following are the most important for our overall well-being.


During each day our brain goes through several neural activities. These activities accumulate a waste product known as metabolic waste. When we have too much metabolic waste, it can affect our memory and neurological system. Research from a South Australian Health and Medical Research Institute has shown that it has been linked to Alzheimer’s disease, and other neurological disorders.

We know that our body works 24/7 flushing waste matter and toxins out of the body. However, when we are sleeping, this process is twice as fast. It’s an interesting process that our brain goes through during sleep.

As we are sleeping, our brain cells shrink by around 60%. This process allows the brain’s glymphatic system to take over and remove waste more effectively. This is why our minds feel much clearer and fresher when we wake up.

Memory consolidation

We have three main subprocesses to our memory function; encoding, consolidation, and retrieval.

The encoding process is where we perceive outside stimuli and form a new trace memory. This process is vulnerable to memory decay and influences that disturb our train of thought, which leads to forgetting. The consolidation process is where that trace memory slowly becomes more stable, integrating and strengthening that memory into our existing network of knowledge. The retrieval process is where we can access and recall that stored memory.

Our long-term memory is maintained and strengthened by a process called memory consolidation. When our sleep is broken and fragmented, it has a detrimental effect on our ability to form solid and emotional memories. Being able to retrieve and form memories is what lets us adapt our behavior to our ever-changing environment. Sleep is the most optimal time for memory consolidation to happen.

Metabolic health

Our metabolism is not only what burns fat, but also what keeps things like our blood sugar, cholesterol, blood pressure, and triglycerides in check. When we get less sleep, our body burns off less energy from fat and more from protein and carbohydrates. This can lead to muscle loss and weight gain.  Also, when we don’t get a sufficient amount of sleep, or have abnormal sleep cycles, it can lead to metabolic syndrome and insensitivity to insulin. This puts you at a greater risk for heart disease and diabetes.

So, you can see why sleep is critical for your physical and mental health.

How much sleep do we need?

how long should i sleep
We now sleep less than we did 30 years ago

You can ask several people and get a different answer from each one. Some people seem to do fine on less sleep than others. Others find they can’t function properly unless they get at least 8 hours of sleep.

Research on sleep has been done by both Washington University and the University of Pennsylvania on how much sleep we need. They took 48 people who were healthy and had an average of 7 to 8 hours of sleep regularly. These were then split into 4 groups. In the first group, participants had to go without sleep for 3 days straight. With the second group, they were only allowed 4 hours of sleep each night. The third group was allowed 6 hours of sleep a night, and the fourth group was allowed 8 hours per night. Groups 2, 3, and 4 were made to stick to these patterns for a period of 2 weeks. During this research, all participants’ mental and physical performance were tested.

With group 4, who were allowed 8 hours per night, there was no decrease in cognitive ability, lapses in attention, or a decline in their motor skills for the entire 2 week period. However, in the second and third groups, who were only allowed 4 hours and 6 hours a night, there was a steady decline in all areas, with the 4-hour group being affected the most.

Research on Sleep Debt
Sleep debt is the cumulative effect of not getting sufficient sleep

It was the 6-hour group that had some interesting results. The researchers stated that “sleep debt” or the effects on the body of lack of sleep, accumulated over time. So, the 6-hour group had 25% of its members falling asleep at various times during the day after 1 week. When they hit the 2 week period, the effects were similar to those who had been up for 2 days with no sleep.

What this shows us is that only getting 6 hours of sleep a night can have the same detrimental impact after two weeks, as it would on someone who has been awake for 48 straight hours.

Sleeping less so that you can get more done actually has a reverse effect. Our performance drops, which negates any benefits we think we are getting. Our ability to notice this drop in performance is also affected, according to the above research. Going back to “sleep debt”, the question asked is, when does it start to build up? It is believed that the breaking point is between 7 to 7.5 hours. Experts state that adults need between 7 to 9 hours of sleep per night in order to function properly. Teenagers, children, and older adults need more hours per night.

Cumulative stress

Cumulative stress is something commonly experienced by people who are constantly working in stressful environments. Stress accumulates from things like a heavy workload, shift work, not being able to relax, and dealing with situations that make you feel powerless. The early warning signs of cumulative stress are depression, a vague feeling of anxiety, emotional fatigue, and apathy. These can develop into other mild and ongoing symptoms, such as intense emotional and physical fatigue, and addiction to alcohol and drugs.

Author James Clear gives a great explanation of cumulative stress. In his example, he uses a bucket to represent our energy and health.

As we go throughout the day we fill our bucket up with things like sleep, recovery, meditation, and laughter. However, he shows that there are other things that work to empty our bucket, like anxiety and stress.

Cumulative stress bucket scenario
Let go of stress and anxiety to ensure a good night’s sleep

A balanced and productive life needs a good flow of things going in and out of the bucket. However, even outputs that are positive and help produce something of value in your life can drain your bucket. These are what are referred to as cumulative.

To keep your energy levels from draining away over time, you need recovery and sleep to fill your “bucket”. If we just keep letting things drain us, we finally come to a point where we are forced to stop and rest because we have either become ill or have injured ourselves. The point is, you need to make that time to rejuvenate and rest before life does it for you.

Does extra sleep really work?

Can we reverse the negative effects of a few bad nights of sleep? Does catching up on sleep over the weekend improve our overall well-being? Research has found that, while extra sleep can alleviate physical symptoms of sleepiness during the day, it has very little impact on one’s cognitive performance.

So, trying to catch up on sleep that you lost during the week isn’t going to restore your attention and focus. It’s only through getting enough sleep every night that you will be able to maintain your performance levels.

Sleeping in over the weekend
Sticking to a sleeping routine makes a huge difference

How sleep works

Let’s take a look at what happens during our sleep cycles. A process referred to as the sleep-wake cycle is what determines the quality of our sleep. We have two main parts of this cycle; slow-wave sleep, which is also referred to as deep sleep, and REM, or Rapid Eye Movement sleep.

Slow wave sleep

When we are experiencing slow-wave sleep, our body relaxes, blood pressure drops, breathing becomes regular, and our brain is less responsive to outside stimuli. During this stage, it is more difficult to wake. This stage of deep sleep is important for the body’s repair and renewal process. It’s when the pituitary gland releases a growth hormone. This hormone is responsible for muscle repair and tissue growth, as well as allowing the immune system to repair itself.

REM sleep

REM sleep does to the mind what slow wave sleep does to the body. It’s the part of the sleep cycle when the brain lights up, when we dream, and when the brain takes information and re-organizes it. Information that is not needed is cleared away and our memory gets boosted as the brain takes our experiences from the past 24 hours and links to previous experiences. It also aids our neural and learning growth. During REM sleep our heart rate increases and blood pressure rises along with our body temperature. The REM phase of sleep occurs 3 to 5 times a night in short bursts.

Without both of these sleep phases, our body begins to die. Just like starving yourself of food or water, when we starve ourselves of sleep, our body isn’t able to recover physically. Our immune system starts to weaken and our brain becomes clouded. Our risk of viral infections rises, as do the chances of mental illness, weight gain, heart disease, high blood pressure, and diabetes.

Sleep and ageing

Research done at Harvard Medical School on sleep and aging has shown that, as we age, it can take us longer to fall asleep. This is referred to as increased sleep latency. Our sleep efficiency, which is the amount of time that we spend asleep, also decreases. We’ve learned that slow-wave sleep cycles are when the body rejuvenates and heals. What this means is that getting less slow-wave sleep can accelerate our aging process because the body isn’t getting enough time to heal and rest.

Circadian rhythm

Our sleep-wake cycle is determined by something called the circadian rhythm. This is a biological 24-hour cycle involving a number of processes. A typical 24-hour cycle that begins at 6 AM would look something like this:



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6 am

7 am

9 am

10 am

2:30 pm

3:30 pm

5 pm

7 pm

9 pm

10 pm

2 am

4 am



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our cortisol levels start to build up to wake the body and brain

the production of melatonin stops

there is a peak in the production of sex hormones

there is a peak in our level of mental alertness

our motor coordination is at its best

our reaction time is at its best

our muscle strength and cardiovascular efficiency is at its peak

our body temperature and blood pressure are at its highest

the production of melatonin starts as it prepares our body for sleep

suppression of bowel movements as the body slows down

when sleep is at its deepest

body temperature is at its lowest[/mks_two_thirds][/mks_col]

What impacts circadian rhythm?

There are 3 factors that have an impact on our circadian rhythm: melatonin, light, and time.


Melatonin is a hormone that is responsible for controlling our body temperature and causing drowsiness. The production of melatonin follows a daily rhythm, where it begins to increase after dark, and starts to decrease when it’s light. It’s believed that the sleep-wake cycle is kept on track by the cycle of melatonin production.


Light is what sets the pace for the circadian rhythm cycle. We can actually reset our circadian rhythm cycle by staring at a bright light for 30 minutes. It’s when the sun rises and light hits our eyes that the transition of a new circadian cycle is triggered.


Things like our daily schedule, time of day, and the routine in which we perform our tasks also has an impact on our sleep-wake cycle.

2-Process model of sleep regulation

A framework for sleep, referred to as the 2-process model, was written about in 1982 by Dr. Alexander Borbely. This was published in Human Neurobiology. He explained how there were 2 processes that occur together when sleeping, which work to regulate our sleep and wake states.

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Process 1

This process is referred to as sleep pressure. Dr. Borbely wrote that, from the moment we awaken, sleep pressure begins to build until we eventually go to sleep. This pressure decreases as we sleep. Getting enough sleep means that you begin the next day with a lower level of sleep pressure.


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Process 2

He describes process 2 as the wake drive. This is meant to counteract the sleep pressure. It is controlled by a repeating 24-hour rhythm wave pattern.

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Sleep scientist, Dan Pardi pointed out that, over millions of years, we have evolved to sleep when it is dark and wake when its light. But, in modern times, most of us work indoors all day in offices that can be darker than it is outside. At night, we sit in front of bright screens and other electronic media. All of this goes against out naturally occurring cycles, wreaking havoc with our circadian rhythm.

Middle aged man sitting in front of laptop in bed at night time
The evening is your time to recharge. Unplug.

This is what results in us feeling drowsy during the day and causes us to find it hard to settle in to sleep at night.

When is it best to go to sleep?

Does it make a difference when you go to sleep if you are getting those necessary 8 hours? It can make a difference. Our pattern of REM and non-REM sleep changes throughout the night. Earlier in the night, we have more non-REM sleep and more REM sleep as we get closer to sunrise. It stands to reason that, if you go to bed really late, you may not get the amount of deep sleep you need.

The recommended window for when to go to bed is between 8 pm and midnight.

This will vary from one person to the next.


As we can see, sleep plays an integral role in our mental and physical well-being. Trying to sleep less to do more doesn’t really work because of the detrimental impact fewer hours of deep sleep has on our cognitive abilities. Our brain needs sleep to get rid of toxins and keep our memory functions fresh, and the body needs sleep to restore and keep the body functions regulated. Setting a good routine that you stick too can help get your sleep pattern back on track, which will have a positive impact on your overall well-being.

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