Why do we need sleep?

Last Updated on August 16, 2021

Sleep is an essential function which helps your body and mind to recharge for the day while leaving you refreshed when you wake up. If you get enough healthy sleep, your body will be healthier, and you’ll be able to stave off diseases. In addition, the brain cannot function properly without enough sleep. Your ability to concentrate, think clearly, and process memories can be affected by this.

The average adult requires between seven and nine hours of sleep a night. Children and teens need more rest, especially if they are younger than five years old. Work schedules, day to day stressors, a disruptive bedroom environment, and medical conditions can all prevent us from getting enough sleep. Chronic lack of sleep may be the first sign of a sleep disorder, but a healthy diet and positive lifestyle can help ensure adequate sleep each night.

That’s why in today’s article, we’ll try and explain ‘Why do we need sleep?’ how much sleep we need and what can happen when we don’t get the rest we need.

Why do we need sleep?

Why do we need sleep?

There are a lot of unanswered questions when it comes down to rest. Many experts agree that there is more than one explanation for why we need sleep. However, it is necessary for a lot of biological reasons. Scientists have found that sleep helps the body in a variety of ways. They include the following prominent theories and reasons:


Why do we sleep?

Generally speaking, we need sleep in order to conserve energy. When we sleep, we reduce our caloric needs by spending part of our time functioning at a lower metabolism level—our metabolism drops during sleep, which is backed by this concept.

According to research, 8 hours of sleep can produce a daily energy savings of 35%. According to the energy-saving theory of sleep, the primary purpose of sleep is to reduce a person’s energy use during times of the day and night when it’s inconvenient and less efficient to hunt for food.

Brain function

According to the brain plasticity theory, sleeping is needed for brain function. It allows the reorganization of your nerve cells. Your brain excretes waste from the central nervous system when you sleep. Toxic byproducts build up throughout the day in your brain, so sleep helps you remove them. As a result, your brain is able to function well when you wake up.

According to research, sleep contributes to memory function. It does so by converting short-term memories into long-term memories and by forgetting unneeded information that may otherwise bother a person’s nervous system. Sleep can affect many aspects of your brain function, such as your learning ability, problem-solving skills, focus and concentration and even your decision making and memory.


Effects of not getting enough sleep

Sleep has an effect on your weight by controlling hunger hormones in your body. For example, ghrelin and leptin are hormones that increase the feeling of being full. These hormones decrease during sleep because you are using less energy.

However, lack of sleep increases leptin and ghrelin. This causes you to feel hungrier, which increases the risk of eating more calories (a.k.a. overeating). Studies show that chronic sleep deprivation, even as few as five consecutive nights of short sleep in a row, may be associated with obesity, type 2 diabetes and metabolic syndrome

Emotional state

Similarly to your physical health, sleep is necessary for your emotional health. Brain activity increases in areas that regulate emotion during sleep, supporting healthy brain function and emotional stability. The areas of the brain that are active during sleep are the amygdala, the hippocampus, the insula, the striatum and the medial prefrontal cortex.

For example, the amygdala is a part of the brain that helps regulate emotion. This brain area is in charge of the fear response and is situated in your temporal lobe. When facing a perceived threat, it is what controls your reaction. The amygdala is able to respond in a more adaptive way when you get enough rest. With that said, if you’re sleep-deprived, the amygdala is more likely to overreact.

According to research, sleep and mental health go hand in hand. Sleep issues can contribute to the start and progression of mental health issues, but they can also contribute to sleep disorders. That’s why you should consider speaking to a professional if you’re constantly having trouble sleeping. In the meantime, you can take a look at our guide on ’30 Proven Tips & Useful Techniques on how to Sleep Better at Night.’

Cellular restoration

The body needs sleep to heal itself, according to the restorative theory. It is believed that sleep allows cells to repair and regrow. Many vital processes that happen during sleep are supported by this. They include tissue growth, muscle repair, protein synthesis, hormone release, etc. 

Heart health

Health issues related to sleep

Scientists think sleep supports heart health, even though the causes are not entirely clear. This is related to the link between heart disease and poor sleep quality. According to the CDC (Centers for Disease Control and Prevention), an average adult needs 7 to 9 hours per night.

On a regular basis, getting less than that can lead to health problems and hurt your heart health. Not getting enough rest is often associated with risk factors for heart disease, including high blood pressure, elevated cortisol levels, insulin resistance and increased sympathetic nervous system activity.

However, most individuals don’t think about the issues that come with oversleeping. Lack of rest and too much of it can both be harmful. If you want to learn more on the subject, check our article on ‘Is too much sleep bad for you?

What are the stages of sleep?

What are the stages of sleep?

An internal ‘body clock’ regulates your sleep cycle, meaning it controls when you feel sleepy and ready for bed. The set clock operates on a 24-hour cycle, also known as the circadian rhythm. This sleep drive may be linked to the brain’s production of a compound called adenosine. Overall, adenosine levels increase through the day as you get tired, and then your body breaks down this compound while you’re in blissful slumber.

Light can also influence your circadian rhythm. The suprachiasmatic nucleus is a group of cells in the brain that process signals when the eyes are exposed to light. With these signals, the brain determines whether it’s day or night.

Melatonin will be released by your body in the evening when natural light is no longer present. In comparison, the body releases cortisol when the sun rises in the morning to promote energy and alertness. Our bodies follow a four-stage sleep cycle once we fall asleep. They are the following:

Stage 1 NREM

Light sleep is the first stage that marks the transition between wakefulness and sleep. That’s when your muscles relax, and your heart rate, breathing, and eye movements begin to slow down. Your brain waves also go down as your begin to rest. This first stage usually lasts several minutes.

Stage 2 NREM

The second NREM sleep stage is characterized by deeper sleep as your heart rate and breathing rates slow down, and your muscles become less tense. Eye movements will stop, and your body temperature will decrease. Brain waves remain slow despite some brief moments of electrical activity. Typically the second stage is the longest of the four.

Stage 3 NREM

The third stage plays an essential role in making you feel refreshed and alert the next morning. The muscles are as relaxed as they will be, and all activity reaches its lowest levels. The stage will be longer at the beginning and decrease as the night progresses.


The first REM (rapid eye movement sleep) stage occurs about 90 minutes after you fall asleep. The name implies that your eyes will move quickly under your eyelid. As a result, blood pressure, heart rate, and breathing will start to increase. It is believed that REM sleep will cause your arms and legs to become paralyzed in order to prevent you from acting out on your dream.

As the night progresses, the duration of the REM sleep cycles increases. REM sleep is associated with memory consolidation, the process of converting recently learned experiences into long-term memories. As you age, the duration of the REM stage will decrease, which will cause you to spend more time in the NREM stages.

The four stages will be repeated throughout the night until you wake up. The average duration of each cycle is 90 to 120 minutes. Most of the time, NREM sleep makes up 75% to 80% of each cycle. You may wake up briefly during the night but not remember it at all. 

How much sleep do you need?

How much sleep do you need?

Depending on your age, the recommended amount of sleep may differ. Of course, there can be variations from person to person, but the CDC (Centers for Disease Control and Prevention) suggests the following durations based on age:

  • 0 to 3 months: 14 – 17 hours
  • 4 to 12 months: 12 – 16 hours (including naps)
  • 1 to 2 years: 11 -14 hours (including naps)
  • 3 to 5 years: 10 -13 hours (including naps)
  • 6 to 12 years: 9 – 12 hours
  • 13 to 18 years: 8 – 10 hours
  • 18 to 64 years: 7 – 9 hours
  • 65 years and older: 7 – 8 hours

What happens when I don’t get enough sleep?

What happens when I don’t get enough sleep?

For most adults, at least seven hours of sleep each night is needed for proper cognitive and behavioural functions. There can be severe repercussions if you don’t have enough rest. Studies show that sleep deprivation can leave people vulnerable to attention lapse, delayed reactions, and mood changes.

People can become tolerant of chronic sleep deprivation. They may not be aware of their own deficiencies because less sleep feels normal to them, even though their brains and bodies struggle due to lack of sleep. That is associated with a higher risk for certain diseases. These diseases include obesity, type 2 diabetes, high blood pressure, heart disease, stroke, and sometimes even poor mental health.

If you don’t get enough sleep each night, you can change your lifestyle and sleep habits to log between seven to nine hours of sleep. You can improve your habits by establishing a realistic bedtime and sticking to it every night. Also, you should maintain a comfortable temperature level in your bedroom.

You can’t forget about creating a more comfortable sleep environment, which typically includes buying a quality mattress, pillows, sheets and duvets. Plus, there are things that you should abstain from at night, such as caffeine, alcohol, tobacco and large meals. 

Overall, for your body to function correctly, you need to get at least seven hours of sleep, be mindful of your habits and keep good sleep hygiene.

Bottom line

To conclude our guide on ‘Why we need sleep,’ we want to say that rest is essential for functioning well and keeping us healthy. Sleep is what lets your body and brain repair, restore, and reenergize at night. Side effects of not getting enough rest include poor memory and focus, weakened immune system, and mood changes.

The average adult needs 7 to 9 hours of sleep each night. If you are having trouble sleeping, speak to your doctor or a sleep specialist. They can help you find the underlying cause of your problems. Now it’s our turn to hear from you if any questions regarding the subject were left unanswered. If you want to share some information, we would gladly hear about it in the comments below.

Isabelle Harris
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