Why Do We Need To Sleep? 

Why Do We Need Sleep
Although human beings need sleep, its biological purpose remains a mystery. Sleep affects nearly every type of body tissue and system - from the brain, lungs, and heart to immune function, disease resistance, and metabolism. Various sleep studies prove that a chronic lack of sleep heightens the risk of health disorders, including depression, diabetes, and high blood pressure.

But, the question remains: Why do we need to sleep? Is there a key role of sleep, or does it serve many functions?

Brain Basics: The Science Behind Sleep

Your brain has structures that regulate your body's natural daily rhythms, such as the circadian rhythm, to help determine when to fall asleep and wake up. This internal clock controls biological patterns, including blood pressure, body temperature, and the release of hormones. Within minutes after falling asleep, significant shifts start to affect both your brain and body. Brain activity ramps down, body temperature drops, and heart rate slow as well.

After waking up, you'll become extremely tired during the day. These feelings then peak in the evening and will increase rapidly during bedtime. This sleep drive (sleep-wake homeostasis) can be linked to an organic compound known as adenosine, produced in the brain.

Exposure to light also influences the circadian clock. The hypothalamus in your brain contains a cluster of cells that process signals when your eyes are exposed to light. These signals will help your brain differentiate between day and night. As the evening starts to approach and natural light disappears, your body will release a hormone that induces drowsiness.

Night shift workers often have a hard time sleeping when they go to bed and staying awake at work as their sleep-wake cycle, and natural circadian rhythm are disrupted. When it comes to jet lag, your circadian rhythm gets out of sync when you do activities like traveling to different time zones. This creates a mismatch between your internal clock and the actual clock.

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Stages of Sleep

People usually progress through a series of physiological stages during sleep. Each stage serves a vital role in keeping your body and brain healthy. There are two main types of sleep divided into four stages - REM (rapid eye movement) sleep and non-REM sleep (has three different stages). They're all linked to specific neuronal activity and brain waves. You cycle through all these stages several times at night, with longer and deeper REM periods happening toward morning.

Here's what actually happens in each stage of sleep.

Stage 1

This is the first non-rapid eye movement sleep stage which acts as the transitional stage from wakefulness to sleep. During this period of light sleep, your eye movements, heartbeat, and breathing slow with occasional spasms. Your brain waves also start to slow from their wakefulness patterns. Any slight disruption during this early stage of the sleep cycle is enough to wake you up from your sleep.

Stage 2

This is a light sleep period before you enter deeper sleep. Here, your breathing and heartbeat slow even further. Eye movements stop and body temperature drops. Brain wave activity also drops, though it's marked by slight bursts of electrical activity. People always spend more of their repeated sleep cycles in this stage than in other sleep stages.

Stage 3

This is the deepest part of non-REM sleep. It occurs in longer periods within the first half of the night. In this stage, your breathing and heartbeat slow to their lowest level, and your muscles relax even more. Deep sleep plays a vital role in effective thinking and memory as well as recovery of the body.

Stage 4

This is the only period of REM sleep. It occurs about 90 minutes after you fall asleep. During this stage, brain activity picks up increasingly and most of your body parts experience temporary paralysis, save for the eyes and breathing muscles. Your breathing becomes faster and your blood pressure and heart rate increase nearing waking levels. Although dreams can occur in any stage of sleep, the most intense ones occur during REM sleep.

Sleep Mechanism

Two internal biological sleep mechanisms, homeostasis and circadian rhythm, work together to control your sleep and waking hours. As earlier mentioned, the circadian rhythm controls a wide range of functions, from regular fluctuations in wakefulness to metabolism and body temperature.

Sleep-wake homeostasis, on the other hand, keeps track of and controls your need for sleep. It reminds your body to sleep after a specific time and regulates the sleep intensity. The homeostatic sleep drive gets stronger with every hour you're awake, causing you to sleep longer, especially after a period of sleep deprivation.

How Much Sleep Do We Need?

Generally, your need for sleep changes as you age. For instance, infant sleep habits differ greatly from grown-ups' sleep patterns. Babies sleep as much as 18 hours per day, which boosts the growth and development of their brain and body in general. Teens and school-age children need approximately 9 hours of sleep a night. Most adults, on the other hand, need about 7-9 hours of sleep each night. However, after you clock in the age of 60, nighttime sleep becomes shorter and lighter.

It also tends to be interrupted by multiple awakenings, depending on how good or bad your sleep hygiene is. 

Benefits of Getting Enough Sleep

Although even sleep experts are yet to reach a consensus explanation for why people need sleep, many indicators support the aspect that sleep serves a vital biological function. From an evolutionary point of view, the fact that nearly every animal species sleep is a clear indication that sleep is fundamental to well-being.

In human beings, sleep appears to be essential to both mental and physical development in children. A lack of sleep in adults has been associated with various health consequences such as impaired thinking and memory and a weakened immune system. These diverse effects of chronic sleep deprivation clearly show that sleep is a vital contributor to the proper functioning of almost all body systems.

Some of the importance of getting enough sleep include;

Energy Conservation

As per the energy conservation theory, human beings need sleep to conserve energy. By sleeping, you'll reduce part of your caloric needs as you spend part of your time operating at a lower metabolism.

This concept is substantiated by the way metabolic rates drop during sleep. Research shows that 8 hours of sleep can produce daily energy savings of up to 35% over complete wakefulness.

Cellular Restoration

Another theory known as the restorative theory suggests that our bodies need sleep to restore themselves. The idea here is that sleeping allows our cells to repair and regrow. This is strongly supported by various crucial processes that occur during sleep, such as;

  • Tissue growth
  • Muscle repair
  • Hormone release
  • Protein synthesis

Brain Function

The brain plasticity theory suggests that sleep is necessary for brain function. Particularly, it allows your nerve cells and neurons to reorganize. As you sleep, your brain's waste clearance (glymphatic) system removes waste from your central nervous system.

It clears out toxic byproducts from the brain, which build up during the day, thus allowing it to function well when you wake up. Sleep affects various aspects of the human brain function, including;

  • Creativity
  • Focus
  • Memory
  • Decision making

Weight Maintenance

Sleep affects our weight by managing hunger hormones. These hormones include leptin, which makes you feel satisfied after eating, and ghrelin, which increases appetite.

When you sleep, ghrelin levels decrease since you're using less energy at night than during the day when you're awake. Lack of sleep, however, increases ghrelin and suppresses leptin. This makes you hungrier, increasing the risk of eating more and gaining weight.

Heart Health

Although the exact causes aren't clear, sleep experts believe that sleep supports heart health. This mainly stems from the connection between poor sleep and heart disease.

The CDC (Centers for Disease Control and Prevention) says an average human being requires 7-8 hours of sleep per night. Consistently sleeping for fewer hours than the recommended range can lead to health issues, many of which can cause harm to your heart.

Lack of sleep is linked to risk factors for heart disease such as;

  • Increased inflammation
  • High blood pressure
  • Elevated cortisol levels
  • Increased sympathetic nervous system activity

Emotional Well-Being

Sleep is also necessary for emotional health. When you sleep, brain activity rises in specific areas that control emotion, hence supporting emotional stability and healthy brain function.

Some of the areas in your brain where sleep increases activity include the insula, striatum, amygdala, and hippocampus. One instance of how sleep regulates emotion happens in the amygdala.

Located in the temporal lobe, this part controls the fear response. It's in charge of how you react when you encounter a perceived threat, such as a stressful situation.

Getting enough sleep helps the amygdala to respond and function more adaptively. However, it's more likely to overreact if you're sleep-deprived.


Generally, a strong and healthy immune system depends on sleep. When you sleep, your body produces cytokines, which are proteins that help fight inflammation and infection. It also makes certain immune cells and antibodies which work together to destroy harmful germs, thus preventing sickness.

What Happens If You Don't Get a Good Night's Sleep?

Without enough sleep, your body will have a difficult time functioning correctly. Sleep deficiency is associated with chronic health issues affecting the brain, heart, blood, and mental health.

Lack of sleep is also linked to an increased risk of injury both in children and adults. For instance, driver drowsiness can lead to severe car accidents and even death. Specific consequences of poor sleep anxiety, depression, poor memory, and mood changes.

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Closing Thoughts

Good sleep is crucial to your health. To make your days as safe and productive as possible, ensure you get a good night's sleep regularly. If you often have trouble sleeping, talk to your physician who'll provide medical advice on how to get the most of your sleep.

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