Why do we need sleep?

Alon Avidan, MD
There are many theories concerning the function of sleep. One of these is that during sleep, a system in our brain essentially cleans toxins and by-products out of the brain tissue. 

This system is effective and active only during the night. If you don't get enough sleep, proteins tend to accumulate and it's been shown that there is a potential accumulation of beta-amyloid, which is the building block of what is found in Alzheimer's disease and dementia. 

Another theory concerns memory consolidation. During the day, you accumulate a lot of information. This information has to be consolidated, and the only effective way to do that is during the night. All this information gets consolidated, making room for more information that you need to store for survival. 
Dawn Marcus
No one really knows the full answer to the age-old question of why we need sleep. What we do know is that sleep is essential to good health. During sleep, there are important shifts in a wide range of chemicals in the body, including those that regulate blood sugar and metabolism, hormones important for immune system function, and brain chemicals such as catecholamines. The catecholamines are "fight-or-flight" substances that include epinephrine, norepinephrine, and dopamine, which are also important pain messengers.
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No one knows the answer to this question but we have some ideas. The basic theories come down to physical restoration, and mental organization. Since all animals require sleep we consider it a necessity. Some of the most important functions of sleep appear to be:
Memory consolidation (moving information from your short term memory to your long term memory, in addition to the organization of thoughts. Some type of brain and body restoration. Think beyond “recharging of your batteries.” It can be a time where the body heals itself from damage it has sustained during the day’s activities. Energy conservation. When asleep we are not using our mental or physical power and this helps conserve energy for when we may need it.
Dr. Michael Roizen, MD
Internal Medicine
Our bodies make us sleep because our brains need sleep the way trains need tracks—they don't work without it. Sleep exercises the part of your brain that you don't normally use. What do I mean by that? Think back to cavemen. They spent each day focusing on the tasks that would keep them alive: hunting, cooking, caring for the tribe. During the day, other parts of the brain—say, the creative parts that would allow cavemen to come up with solutions and ideas for stronger weapons or shelter—didn't get used because the cavemen were so caught up with living and surviving in the moment. That is, except during sleep, which is what allows those creative parts to strengthen and grow so that they'll be fully developed when the situation arises to use them.

No one really knows why we need sleep but there are theories:

  • Sleep can give the body time to repair muscles and other tissues and to replace aging or dead cells.
  • Sleep can give the brain time to organize and archive memories. Some people think dreams are part of this process.
  • Sleep can lower our energy consumption, so we need only three meals a day rather than four or five. We can't do much in the dark anyway, so we might as well "turn off" and save energy.
  • Sleep might be a way to recharge the brain.

What we do know is that, with a good night's sleep, everything will look and feel better in the morning. Both the brain and body are refreshed and ready for a new day.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.