Why Do We Sleep?

Why do we sleep?

Sleep. That thing we all need and sometimes crave. Throughout history, people have wondered and theorized why we, as humans, need sleep. For years, this has been a conundrum that scientists and doctors have questioned. Why is sleep necessary? How can we determine the reasons why sleep helps us get energy throughout the day? Let’s start with what we know.

Sleep: The Facts

We know by now that we all need at least seven hours of sleep a night. While this quantity is important, it’s also important to measure the quality of sleep, by making sure those seven hours of sleep are spent in REM sleep, which can be measured by the rapid eye movement one makes when they are deep in unconscious sleep.


Sleep can be linked to preventing obesity, heart disease, Alzheimer’s, and even cancer. As much as we don’t know about the reasons for sleep, we know the benefits of getting a good night’s rest.


We also know that sleep helps with memory, energy, and executive brain function and that, if we don’t get the right amount and quality of sleep it can poorly affect your day and work performance.


Doctors have also determined that sleep disorders exist, where people have an inability to fall asleep and stay asleep throughout the night. This can be caused by sleep apnea and insomnia. There is also narcolepsy, which can cause people to fall asleep at seemingly random times of the day.

There are many sleep theories

Sleep Theory

The underlying question, why do we sleep, still haunts researchers today. We have no proven answer that that question, but we do have common theories that might help explain why we sleep- if they ever get proven to be true.


There are four common theories as to why we sleep. They can be labeled as:

  • Inactivity theory
  • Energy conservation theory
  • Restorative theory
  • Brain plasticity theory

Inactivity Theory

Inactivity theory suggests that sleep became a practice we adapted as a response to staying safe from predators at night. Supposedly, animals who were able to stay still and quiet throughout the night were more likely to survive than those who stayed active.


Energy Conservation Theory

Energy conservation theory is as it sounds. Since competition and survival are key in the wild, theorists believe that sleep became a way for predators to conserve their energy to better hunt during the day. Research shows that metabolism is slowed when people are asleep, meaning they are less likely to burn as many calories during nighttime as they are in the daytime. Because of this and the similarities, it has to inactivity theory, energy conservation remains a dominant theory among sleep researchers.


Restorative Theory

Restorative theory suggests that the body needs sleep to restore what is lost during the day. This theory has been elevated by evidence that shows that depriving animals of sleep will cause them to lose brain function and, eventually, die. Studies show that muscle growth, protein synthesis, and certain hormones are released during sleep more so than any other time. This theory also points to a restoration in cognitive function, which would explain why good sleep makes you feel awake in the morning.


Brain PLasticity Theory

The brain plasticity theory is the most recent theory circulating sleep researchers. Brain structure and organization have been linked to sleep in some studies. This is referred to as brain plasticity, and it is crucial in infants and young children. While brain plasticity remains somewhat of a mystery, this theory could explain why losing sleep is so detrimental to one’s health.


What now?

Given all these theories, it’s hard to pinpoint one reason why we sleep. Maybe one of these theories is correct or maybe it’s a combination of all of them. Regardless, there seems to be one thing for certain: we need sleep in order to maintain a long and healthy life.

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