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The Power of Sleep

What is sleep?

Everyone would definitely have heard of sleep, but do you know what sleep is?

Sleep is medically defined as “a natural periodic state of rest for the mind and body, in which the eyes usually close and consciousness is completely or partially lost, so that there is a decrease in bodily movement and responsiveness to external stimuli”. In other words, sleep is a recurrent state whereby responsiveness to external stimuli is reduced and predictable physiological changes occur.

Sleep is one of our bodies’ most important functions. Most animal survival instincts - including the need to hunt, gather, eat, reproduce, and defend ourselves - are put to a halt when we sleep. This essentially implies that sleep is necessary for our survival in a different way.

In general, sleep improves our cognitive abilities along with our body’s ability to function. Long-term effects of a lack of sleep include a weakened immune system, poor balance, high blood pressure and even risk of heart disease.

In this article, we will dive deeper into why sleep is important, the mechanism of sleep and different medical conditions associated with sleep.

Why sleep is important

Sleep takes up a very big chunk of our day – approximately one third of your day as a matter of fact! Sleep is also a fundamental human requirement (i.e. it is as essential as food, water, and shelter).

According to Dr. Thomas Roth, “the number of people who can survive on five hours of sleep or less without impairment, and rounded to a whole number, is zero”. In addition, Matthew Walker claims in his book - Why We Sleep. Unlocking the Power of Sleep and Dreams - that “the shorter you sleep, the shorter your lifespan”. He also makes reference to how sleep deficiency is one of the world’s most lethal pandemics, stating that “the decimation of sleep throughout industrialised nations is having a catastrophic impact.”

Meanwhile, the Centers for Disease Control and Prevention (CDC) recommends adults to sleep seven or more hours per day, whilst newborns ought to be sleeping for around 14 to 17 hours each day.

What is the reason behind this?

Sleep allows our bodies to recover from the stresses it has been exposed to during the day. Breathing, body temperature and heart rate drop in order to save energy and allow our cells to regenerate.

Sleep also facilitates our memory and learning. Have you ever heard a teacher, or a boss tell you you should get a good night of sleep before an important task? This is most probably the reason. Sleep gives time for our brains to consolidate what we have learnt and imprint them into memories, thus it would be easier for us to recall our tasks the following day after a good night's sleep in comparison to pulling an all-nighter and trying to cram everything in.

Besides that, sleep also has a significant influence on our immune system. In order to fight infections, our bodies naturally produce proteins called cytokines. In fact, the U.S. Department of Health and Human Services noted that your body tends to produce more cytokines when you have the flu, and this partially explains why you may feel exhausted during that period of time. In essence, sleep gives time for the body to produce cytokines and protect itself from infections. Furthermore, there is evidence that a lack of sleep can negatively influence glucose metabolism, even resulting in qualifying someone as pre-diabetic.

In order to understand why sleep is so critical - in fact, critical enough that attempting to deprive oneself from sleep has been banned from Guinness World Records, we first need to take a closer look at the different stages of sleep and mechanisms by which sleep is regulated.

The different stages of sleep

Sleep is commonly divided into two main types, each of which is linked to particular brain waves and activity. These two types of sleep are called the rapid eye movement sleep (REM) and the non-rapid eye movement sleep (non-REM).

Meanwhile, a typical sleep cycle includes four stages of sleep (consisting of one REM and three non-REMs), with each of them repeating several times throughout the night.

Stage 1 (non-REM)

Stage 1 begins when a person becomes somnolent and transitions from wakefulness to sleep. During this stage, heartbeat, breathing and eye movement slow down and muscles relax. The slowdown of brain waves can be investigated with an electroencephalogram (EEG). This is the kind of sleep a person enters when taking a nap. This stage is relatively short, lasting around 5 to 10 minutes and takes 5% of the total sleep time.

Stage 2 (non-REM)

Right after Stage 1, at 10 to 25 minutes of each sleep cycle, a non-REM stage takes place, also known as a period of light sleep. It involves further relaxation of muscles and slowdown of breathing and heartbeat, followed by a stop in eye movement and a drop in body temperature. This stage can be differentiated based on slow brain activity with brief bursts of electrical activity. This stage adds up to 55% of the total sleep time.

Stage 3 (non-REM)

This is the critical period that allows you to feel refreshed when you wake up in the morning. It is what is commonly called “deep sleep” as it is characterized by the brain waves and responses being lowered to the minimum, thereby making it harder to respond to external stimuli (and to wake the person up). Nightmares and sleepwalking are most likely to take place during this stage.

Stage 3 of non-REM sleep usually occurs during the first half of your sleep and lasts between 20 to 40 minutes, a 15% of a total night sleep.

Stage 4 (REM sleep)

This stage takes place 90 minutes after falling asleep and lasts around 10 minutes during the first sleep stages cycle. It then increases as the night continues throughout more sleep stage cycles. Rapid eye movements behind closed eyelids is the main characteristic of this stage. Other features include increased brain wave frequency, faster breathing and higher blood pressure and heart rate, all more similar to that achieved during wakefulness. It is during this stage where dreaming usually occurs. As arms and legs become temporarily paralyzed, it impedes the performance of dreams. It is also during this stage that our brain recalibrates emotion processing and creativity. This sleep accounts for 20 to 25% of an adults’ night sleep and about 50% of an infant’s sleep.

The mechanisms of sleep

The section above explains what occurs when we are asleep.

However, it doesn’t explain how sleep is regulated. Our body has two internal mechanisms that regulate sleep and wakefulness cycles: circadian rhythms and sleep-wake homeostasis.

Circadian rhythms

Circadian rhythms are “physical, mental and behavioural changes that follow a daily cycle”. The body’s biological clock (which is an organism’s innate timing control; composed of proteins that interact with different cells) controls most of these cycles.

These cycles are mainly responses to changes in light, darkness, temperature and other factors in the environment. However, circadian rhythms can also continue without external stimuli for certain periods of time. This therefore explains the jet lag phenomenon where there is a mismatch between your inner biological clock and the real clock. Furthermore, these rhythms can also influence a variety of functions ranging from body temperature, metabolism, homeostasis in addition to making you feel sleepy at night. They are also the reason behind a person's tendency to wake up at similar times every day, even if they didn't set an alarm.

Sleep-wake homeostasis

Sleep homeostasis is the basic principle behind sleep regulation. In other words, it keeps track of your need for sleep by regulating our sleep intensity and reminding the body to rest after a certain time.

The longer you stay awake without sleeping, the stronger the drive for sleep, and this causes you to have a deeper sleep over a prolonged period of time.


Entertaining, fun, romantic, or bizarre on every angle? Your dreams are essentially stories and images created by your mind while you’re sleeping.

The reason behind why we dream is not clear, but there are a number of theories posed by researchers to help explain this. Medical News Today describes some of these theories, and they range from speculations that dreams are possible representations of our unconscious desires and feelings, to postulations that dreams are meant to help us process the information that we have gathered during the day. Perhaps the most interesting theory is that dreaming is a form of psychotherapy that aids our understanding of our deepest thoughts.

Meanwhile, experts have also long debated whether dreams could be the cause of REM. No conclusion has been accepted so far, but different hypotheses are under study. One of the notable ones include the activation-synthesis model of dreaming. This model, proposed by Allan Hobson and Robert McCarley back in 1977, suggested that dreams are caused by our brain’s physiological processes. During REM sleep, some brainstem circuits get activated, particularly those forming part of the limbic system. This includes the amygdala and hippocampus, both of which are involved in memory processing, emotion, and sensations. And as our brain attempts to create meaning from these neural activies, dreams occur as a result.

There were a few interesting studies carried out in an attempt to understand what influences our dreams too. In the famous threat simulation theory of dreaming (TST) study, a group of scientists took a group of Kurdish children who had been severely traumatized and a group of normal, non-traumatized Finnish children and studied the reports of their dreams. One of their findings was that children who had been exposed to trauma and real-life threatening events were more likely to experience a more active threat simulation response, which leads to “increased frequency and severity of threatening events in dreams,” as quoted from the abstract of the study. On the other hand, children living in safe, free and normally non-threatening environments were found to have the opposite effects and a less active threat simulation response. Therefore, they experienced fewer threatening events in their dreams.

To date, none of these theories have proven how dreaming occurs or have established a connection between dreams and REM sleep. Hence, the psychology of dreaming remains a controversial topic among the neuroscience community and more studies need to be conducted in order to draw plausible implications.

Factors that affect our sleep quality

As seen previously, the type of dreams we have had can be an indicative parameter of how stressed we have been when we were in our wakeful state, and these may cause general feelings of distress during night-time or even sleep disturbances.

However, dreams are not the sole components affecting our sleep quality, as there are many other factors such as medical conditions, stress, sleep environment, diet, and medication that can disturb our sleep-wakefulness cycle, thereby causing a detoriation in sleep quality.

Additionally, another key contributor in influencing sleep quality is melatonin. Melatonin, also known as "the sleep hormone", is a naturally occurring hormone and a central part of our body’s sleep-wake cycle. This is because melatonin regulates the timing in which sleep occurs. It is produced by the pineal gland before being released into the bloodstream, and its levels increase during the evenings to induce sleepiness.

On a different note, one of the other main factors that is well-known for hindering the effects of the body’s biological clock is caffeine. Caffeine is a natural stimulating substance that promotes alertness by blocking adenosine receptors. In particular, adenosine is a substance that promotes the feeling of tiredness. Thus, when the effects of adenosine is restricted by caffeine, the individual will feel less tired.

Medical conditions associated with sleep

Sleep disorders come in many forms, but they all have a common symptom – sleep disturbance (or even a lack of sleep entirely!). Some examples of such conditions are discussed below:


Insomnia is a sleep disorder that affects one-third of all adults, with 6 to 10% having enough recurring symptoms to be diagnosed with chronic insomnia according to the American Psychiatric Association (APA).

People with insomnia usually find it difficult to fall and stay asleep for long periods of time. Some risk factors impacting the onset of insomnia include experiencing high levels of stress, having emotional disorders (such as depression and anxiety), and encountering jet lag whilst travelling. Just like the majority of mental disorders, insomnia could occur to anyone. Feeling fatigue, sudden mood shifts, and having concentration difficulties are common symptoms of insomnia.

Cognitive Behavioural Therapy (CBT) is a recommended first-line treatment for the symptoms of insomnia. This type of psychotherapy involves letting the patient understand and recognize the often negative and unhelpful thoughts that they may be feeling, which may also be indirectly restricting their normal sleep cycles. Not to mention, CBT is also commonly used as a first-line treatment for anxiety and depression, which may also contribute to the risk of having insomnia.

Sleep apnea

Sleep apnea is another type of sleep disorder. Sleep apnea can become extremely dangerous as it involves the person having irregular breathing patterns when they are asleep.

In some cases, people with sleep apnea may stop breathing hundreds of times in their sleep. Consequently, this means that they are not getting the oxygen that their brains and bodies need for their normal functioning, and can therefore become a serious health complication.

There are two main types of sleep apnea that are commonly observed in patients: obstructive sleep apnea (OSA) and central sleep apnea (CSA). OSA is more prevalent and is caused by obstructions in the airway of the person. More specifically, OSA involves the soft tissue at the back of a person's throat collapsing against itself in the middle of sleep, thereby cutting away a clear airway for the person to breath. CSA, on the other hand, is caused by abnormalities in the brain's function, whereby the brain fails to signal a clear instruction to the chest muscles to breathe.

Sleep apnea could occur to anyone at any age, but there are certain risk factors that may increase the chance. Being male, overweight, over 40 years old, having nasal obstructions (such as a deviated septum), or even a larger than average neck size could significantly increase the risk of developing sleep apnea.

Although a cure for this condition has yet to be found, continuous positive airway pressure (CPAP) is a common way to treat sleep apnea. It delivers pressure through a mask through the person’s airway to keep it open while the person sleeps. This may be comfortable to some, but may be disturbing to others.


Narcolepsy is a chronic sleep disorder which affects the person’s ability to stay awake. This includes experiencing sudden attacks of sleep and extreme drowsiness. As there is no cure for this condition at the moment, people who suffer with narcolepsy find it extremely difficult – if not impossible – to stay awake for a long period of time, and these have severe consequences in their daily lives.

Narcolepsy is often defined into two categories: type 1 and type 2.

Type 1 narcolepsy

The diagnosis criteria for type 1 narcolepsy includes the detection of low hypocretin (a brain hormone) levels as well as cataplexy (a sudden loss of muscle tone; often triggered by intense emotional experiences such as laughter).

Type 2 narcolepsy

Type 2 narcolepsy patients, on the other hand, do not have cataplexy and generally have less severe symptoms than type 1 narcoleptics.

Besides those two, secondary narcolepsy is also another form of this condition originating from injuries in the hypothalamus. This involves the patient experiencing common symptoms of narcolepsy, having long sleep periods (i.e. over 10 hours) as well as severe neurological issues.


Sleepwalking is often regarded as amusing, but there may be some serious health implications behind it.

Sleepwalking is a type of sleep disorder known as parasomnia, whereby parasomia refers to a set of irregular behaviours that occur during a state of being awake and asleep at the same time. This condition occurs during the third stage of (non-REM) sleep, hence sleepwalking is regarded as an "NREM disorder of arousal".

During a sleepwalking episode, the individual may have their eyes either open or closed. These episodes can last from only a few seconds to half an hour. In fact, a study found that over 29% of children aged 2 to 13 have experienced sleepwalking; whereas in adults, this percentage is a lot smaller (at approximately 4%).

Some examples of sleepwalking include moving furniture, getting dressed or walking on the house and/or streets. It is less common, but also plausible, to encounter violent, embarassing, physically endangering, or more complex behaviours such as driving or writing.

People with anxiety, depression, and/or other mental conditions or injuries tend to be at a higher risk of getting these sleepwalking episodes. But the good news is that these conditions may be treated with therapies such as CBT, as described earlier. When these treatments are not successful at alleviating the symptoms, medications can be given to the patient. These often include antidepressants, benzodiazepines, or even melatonin supplements. However, in most cases, sleepwalking does not require any specified treatment as these episodes often do not pose any risk to the individual or others.

Moving forward

In our world today, the primordial importance of sleep has been largely downplayed by society, thus many believe that skipping several hours of sleep doesn’t have an impact on their health. However, based on what we have discussed, it clearly does.

All in all, sleep is the most effective way for us to recharge our brains and body after a long day. What's more, besides its critical role in helping us retain information, sleep has been also proven to be necessity to help us combat infections and diseases more efficiently.

So, if you want to live a healthier life, don’t look any further! Try a full night of sleep and experience the amazing results!

Extra learning resources for you

Author: Covadonga Piquero Lanciego, BSc Biological and Biomedical Sciences


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