Why do We Need to Sleep?

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  • Written By: Diane Goettel
  • Edited By: Bronwyn Harris
  • Last Modified Date: 26 September 2016
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Sleep is a natural state of rest for members of the animal kingdom. Scientists have observed the sleep of mammals, birds, reptiles, fish, and amphibians. Although we are still not entirely sure of how sleep works, nor are we convinced that we understand all of the functions of sleep, scientists have become convinced that sleep is necessary to survival.

There are a number of theories about why we sleep and what happens in our bodies and brains during sleep cycles. However, there is not currently one predominant theory. It is quite possible that there is a kernel of truth in each of these theories; that they will all work together eventually to inform a more complete understanding of human sleep.

Most scientists agree that one of the major purposes of sleep is to restore and heal the body. It has been observed that hormone and immune functions change during specific stages of the sleep cycle. Furthermore, some studies have shown that sleep deprivation can lead to deficiencies in the immune system. Although it is believed by some that important growth can take place during sleep, there have been no studies to show that the lack of sleep can halt or stunt growth.


It has also been hypothesized that sleep offers important restoration to the brain. It is possible that neurons are restored, that brain proteins and certain hormones are produced. Some scientists believe that sleep is particularly important to the brains in young humans. Sleep deprivation in early life has led to decreased brain mass, permanent sleeping trouble, and behavioral problems. Although many scientists feel that the main function of sleep is not to restore or improve the capabilities of our memory, it has been observed that people have an easier time memorizing information if they have had adequate sleep than if they are sleep deprived.

A completely alternate theory to those described above is the “Preservation and Protection” theory of sleep. This theory asserts that human beings do not require the full 24 hour period within each day to satisfy basic needs such as collecting necessary food and supplies, eating, and reproducing. As not all 24 hours are required, sleep offers a time of rest when humans are not out in the elements, and therefore exposed to threats. Just as the caveman is less likely to be pounced upon by a jaguar while he is tucked inside of his sleeping space, the modern man is less likely to be hit by a bus while sleeping in his apartment. This theory, of course, does not postulate what happens inside of our bodies and brains while we sleep.


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Post 10

“Preservation and Protection” doesn't explain why apex predators need to sleep.

Post 9

True, we might not gain energy from sleep, but it might be a time when our body produces energy from what we eat. Also, since you are pretty much unconscious when you sleep, it might be a tool to help conserve energy.

Post 8

Sleep occurs when night comes. It connects living beings on the planet with the Earths daily cycle and the cycle of Sun and Moon.

To fully understand there has to be a return to natural time, instead of clock time. The female human cycle follows the Moon cycle and nature is part of this whole.

Post 7

Why do I feel more tired when I sleep too much?

Post 5

I don't get the jaguar part. Just because, why does my house cat sleep five hours while it is prey and has a "higher" chance of getting pounced on and a jaguar sleeps even longer than humans? Lions sleep even more than jaguars.

I just thought about it. I don't know. It just seems like the "greater" that the animal is, the more it sleeps maybe. I thought maybe it was just a backward metaphor or something.

Post 4

anon, I believe the brain functions thing comes into play here: when we tire it may be our perception of our body that tells us we are very tired and lack energy. When we get up in the morning what should have been done by the body during sleep is complete and we feel we have more energy because it is time to spend energy on stuff and to accumulate more. In a few words: it may be a trick of the mind.

It may be that we don't see our energy level at a certain time the same way we see the fuel indicator in our vehicles.

Post 3

Why do we feel more energized after a good nights rest when we don't actually take in any more energy(or do we)?

Post 2

How do we know that these cycles do not occur if we stay awake long enough?? Are there studies that look into that?

Post 1

Sleep is beneficial to the immune system, memory, and lets not forget skin. Production of protein during sleep helps with cell growth. In effect the whole body benefits from sleep.

It is suggested that small children sleep sixteen hours a day, teenagers nine hours and adults seven to eight hours, for a healthy, well balanced life.

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