If you Google, why we sleep, you get answers like rejuvenation, memory consolidation, learning, and the like. Those may be side benefits or secondary reason, but they are not the real reason why we need sleep. Once you find out the real reason for sleep, perhaps you, as it was for me, will be more motivated to priority sleep. We as a nation, do not give sleep enough importance that it deserves.
If sleep was only for memory consolidation, then we would not die from lack of sleep. In fact, we die in a fewer number of days from lack of sleep than from lack of food. [reference] We die first from lack of air, second from lack of water, third from lack of sleep, then from the lack of food. If sleep was for learning, we would be stupid, but not dead.
Clearly, there is a more fundamental reason why sleep is biologically necessary in all mammals with brains. Sleep is necessary for the clearing out of waste products from the brain. The brain does not have a lymphathic system to clear waste like other organs; it has a gymphatic system which ONLY operates during sleep. Sleep is when brain cells shrink so that cerebral spinal fluid (CSF) can go between the cells and wash out the toxic by-products from it heavy metabolic use during the day.
Among those by-products that accumulate during the day is beta amyloid. They are cleared at night during sleep. Beta amyloid are exactly those plaques that characterizes Alzheimer’s disease. It has been speculated that ineffective clearance of beta amyloid may be a partial cause of Alzheimer’s disease. We do know that people with Alzheimer’s often also have difficulty sleeping. Perhaps, it is this difficulty sleeping that preceded and contributed to Alzheimer’s. We also know that people with sleep disorders have higher beta amyloid. (Yes, we can see beta amyloid in PET scans) And higher deposits of beta amyloid causes poor sleep. It is a viscous cycle. So it is best to optimize sleep early on in life.
This TED Talks by Jeff Iliff of Oregon University, provides a compelling explanation of why we need sleep…
Study at UC Berkeley found that quality of sleep and memory are related.
Brain injuries, such as concussions, impairs the gymphatic system and increase risk of Dementia.
Read more in my other article Purpose of Sleep is to Clear Brain Waste
Another Reason Why We Need Sleep
Note that clearing brain waste is just ONE of the potentially many reasons why we need to sleep. It is in non-REM Stage 3 and 4 sleep that generate the deep slow wave sleep (SWS) when the pituitary gland increases its secretion of growth hormones. People with the rare disorder of Fatal Familial insomnia can not get pass stage 1 sleep and thus waste away with weight loss as they can not generate growth hormones.