6 Reasons Why Humans Need Sleep

When life gets too busy, sleep is the first thing we sacrifice, be it voluntarily or involuntarily. Ironically, proper sleep is also the thing we need the most when we are working hard.  

Even if we are not exerting ourselves on a daily basis, we need sleep.

When a person is sleeping, it may seem like they are doing nothing. But the complete opposite is true.    

The truth is that sleep is a biological need that is vital for the survival of humans. So much so that a person would die if they go without sleep for more than 11 days.

And after just three days without sleep, a person starts suffering from severe mental health issues such as delusions, paranoia, hallucinations and severe emotional dysregulation.

So, why do humans need sleep biologically?

Sleep is a biological ‘maintenance mode’ that is responsible for the upkeep of almost every system in the body.

Let us explore the reasons why sleep is important for humans—  

1. Proper sleep strengthens your immune system.

While you sleep, your body produces cytokines.

Cytokines are proteins (released by immune and non-immune cells) that aid the immune system in fighting off infections and inflammation.

It also helps in the production of red blood cells.

So, when you lose sleep on a regular basis, your immune system becomes weak.

The immune system is a great example of how a person’s sleep and health are related.

2. Sleep is vital for a person’s physical growth and tissue repair.

When you sleep, energy is diverted towards fulfilling inner tasks such as healing and development.

When you enter the non-REM stages of sleep, your body gets into a super-restorative mode that helps the body in healing, growth and muscle recovery.

In other words, the hormones released during sleep helps a person grow physically as well as mentally. They also help repair damaged tissues and cells.

This is why it is very important for kids and teenagers to get their required hours of sleep; which is between 9-12 hours of sleep per day.    

3. Sleep aids in neurological restoration.

It is a known fact that cognitive functions are deeply related to neurology.

Cognitive processes such as memory retention, language, attention span, and executive functions are physical proofs of neural activity.

And sleep plays a major role in the restoration of neurological functions; and by extension, in the maintenance of cognitive functions.

Wondering why the brain needs sleep?

While a person sleeps, the brain gets busy processing all the information it had gathered during the day.

At this step, the brain basically segregates the information from short-term memory to long-term memory.

Sometimes, the brain also discards the memories that are deemed unnecessary or too mundane.

Another important neurological task the brain carries out while a person sleeps is waste clearance.

Which is basically a plumbing system used to flush out toxins and metabolic waste (such as Beta-amyloid) from the central nervous system.

This process is carried out by the glymphatic system, which is a glial-dependent waste clearance pathway in the brain.      

4. Sleep is important for the regulation of the metabolic system.

Leptin, a hormone produced by fat tissues (called adipose) acts as the primary messenger to the brain.

Leptin is responsible for regulating appetite, metabolism and long-term energy of a person.

In other words, leptin sends the message to your brain when your stomach is full. And that is when you usually stop eating.

Ghrelin— the hunger hormone— produced mostly by the stomach, signals the hypothalamus part of the brain to increase appetite and initiate the process of eating.

Sleep is crucial when it comes to controlling the levels of leptin and ghrelin properly.

When a person does not get enough sleep, the level of ghrelin rises while the level of leptin falls.

As a result, hunger and food cravings increase. The person ends up eating more food than actually required by their body.

This leads to a host of other health complications such as obesity, diabetes and high blood pressure.      

5. Sleep helps in keeping the hormones in balance.

It has already been established that sleep is essential in making sure that the hormones in the body stay in balance.

Insulin is a hormone that is produced by the pancreas. It helps in regulating blood glucose levels.

When it comes to the way a person’s cells respond to insulin, sleep is a major factor.

Whenever a person suffers from sleep deprivation, it increases insulin resistance and reduces insulin sensitivity; even after just one night of improper sleep.

When a person misses proper sleep consistently (sleeping less than 6–7 hours per night), it disrupts their metabolism and causes liver, muscle, and fat cells to resist insulin.

This in turn increases the risk of type 2 diabetes by 28%.  

Proper sleep is important in keeping the cortisol level in check. Cortisol is known as the stress hormone.

A lack of sleep causes the cortisol level to rise, triggering higher stress responses. Eventually, it leads to weight gain and anxiety.

When a person does not get the required amount of sleep, the reproductive hormones (estrogen, progesterone and testosterone) fall out of balance.

When the reproductive hormones fall out of balance, it leads to numerous reproductive-health related issues such as irregular menstruation, disruption in ovulation, preventing egg-release and embryo implantation.

In other words, it creates problems in conceiving a baby. It also creates problems in carrying a baby to full term.

A lack of sleep leads to improper melatonin production. Melatonin is important for regulating the body’s internal clock known as the Circadian rhythm.

Ironically, the Circadian rhythm is responsible for regulating sleep-wake cycles in people.    

6. Sleep is crucial for emotional regulation.

One of the most underrated functions of sleep is emotional regulation. However, it is a very important one.

The amygdala, located in the temporal lobes part of the brain, is known as the brain’s emotional centre.

It helps in processing various emotions such as fear, pleasure and anxiety. It helps in retaining memories. It also helps in determining how a person behaves in a social situation.

The amygdala is also vital in initiating the ‘fight or flight’ response to various threats a person may face, be it real or perceived.

A major benefit of sleep is that the amygdala keeps working the way it should. As a result, you react to things the way you should.

Getting the proper amount of sleep enables a person to have better control over their emotions, handle stressful situations efficiently and maintain an overall steady mood.

A person’s sleep schedule and sleeping habits are determined by their Circadian rhythm.

Click here to learn all about the Circadian rhythm.

Need for Sleep FAQs

How many hours of sleep do humans need?

A minimum of seven hours of sleep is recommended for adults. But the amount of sleep needed by humans can vary from person to person.

Other than age itself, factors like health status and activity level also determine how much sleep a person requires in a 24-hr time period.

According to science, the number of hours of sleep a person needs according to their age falls within a specific range.

This specific sleep-requirement has been mentioned in the table below.

What causes humans to need sleep?

When a person does not get enough sleep, it is very hard for them to maintain and strengthen the neural pathways in their brain.

These pathways are important for storing new information. Hence, it is crucial for memory consolidation and brain detoxification.

A lack of sleep can lead to poor concentration and slowed down responses.

The quantity and quality of sleep also determines how efficiently a person’s neurons (nerve cells) communicate with each other.

If the neurons in the brain don’t work well, then many physical and mental aspects of a person get affected.

So, why do we need sleep scientifically? To be the best we can be, physically, as well as mentally.  

What are the stages of sleep?

Just because you are asleep does not mean that you are totally inactive. Yes, you are less aware of what’s happening around you when you are asleep.

But, there are a number of things happening in your brain while you are asleep. So much so that there is detectable brain activity during a person’s sleep.

Brain activity during sleep follows a certain pattern. Those patterns have been categorized into two main stages— (REM) sleep and non-REM (NREM) sleep.

REM stands for rapid eye movement.

NREM has three stages of its own. When a person falls asleep, they usually enter NREM Stage 1. Then they shuffle between NREM Stages 2 and 3.

Once these stages of sleep are complete, they go into the REM Stage of sleep. This is where all the dreams and nightmares are “seen” by the person.

Once the first REM cycle is complete, they start the sleep cycle again from either NREM Stage 1 or 2.

One whole sleep cycle with all the stages takes about 90-120 minutes, before another begins.

People who get atleast 8 hours of sleep regularly, go through four or five sleep cycles every night.

What are the effects of a lack of sleep?

Missing sleep on just one night can cause poor focus, low energy and reduced decision-making power. It can also leave you irritated.

If you face sleep deprivation for a long period of time, it can lead to a wide range of physical as well as mental health issues.  

Effects of sleep deprivation on the brain and body include—

a. A compromised immune system that does not do its job efficiently. Hence, you fall sick more often than considered normal.

b. Increased chances of having depression, anxiety and other similar mental health issues.

c. Affects how your body’s metabolism works. Therefore, it increases the risk of you becoming obese.

d. Puts you at a greater risk of developing type 2 diabetes and high blood pressure.

e. Elevates the chances of you developing heart diseases.

f. Affects your mood, making you more irritated and impatient. This moodiness can affect your personal and professional life negatively.

g. Causes low energy; which can ultimately affect your productivity, causing problems at work.

Do I have to get all my sleep at once?

No. It is not necessary to complete all the hours of required sleep at once.

It is okay for you to take a nap during the day to fulfill your sleep-requirements if you have not been able to do so during the night.

Sleep customs vary by culture as well as time-period.

In many parts of the world, it is perfectly acceptable for people to take a nap in the afternoon; even if they are at work.

Many communities have their own sweet word for it. For example, ‘siesta’ in Spanish-speaking countries and ‘inemuri’ in Japan.

Historically, it was normal in some parts of the world for people to split up nighttime sleep into two different parts.

They slept for four hours, got up, did some work for a while and then slept for another four hours till it was time for them to get up for another day.

What are sleep disorders and which of them are more common?

Conditions that cause disruption in sleep and/or wakefulness are called sleep disorders.

There are six known types of sleep disorders in the main category. They are—

a. Insomnia.

b. Parasomnias.

c. Circadian rhythm sleep-wake disorders (such as jet lag or shift-work sleep   disorder).

d. Sleep-disordered breathing disorders (such as sleep apnea).

e. Central disorders of hypersomnolence (like narcolepsy).

f. Sleep-related movement disorders (like restless leg syndrome).

There are various sorts of Parasomnias. They are classified on the basis of REM and NREM stages of sleep.

REM Sleep

a. REM sleep behavior disorder.

b. Hypnagogic and hypnopompic hallucinations.

c. Nightmare disorders.

NREM Sleep (Stages 1 and 2)

a. Teeth grinding (bruxism).

b. Exploding head syndrome.

c. Periodic limb movement disorder (PLMD).

d. Sleep starts or twitches (sleep myoclonus).

NREM Sleep (Stages 3)

a. Sleepwalking (somnambulism).

b. Sleep-related eating disorder.

c. Periodic limb movement disorder (PLMD).

d. Confusional arousals (partial waking with sleep inertia).

e. Night terrors.