Genetic research shows that some people need fewer hours of sleep than others. But all humans need sleep. And all animals need rest. Research on sleep and body activity reveals the cognitive and physical benefits of sleep and how sleep acts as a “waste management” for the brain.
Why Do We Sleep? The Explanations
We can group theories explaining why we need to sleep into two categories: inactive and restorative. Recent research on sleep however, favors restorative theories on sleep function.
Previously, researchers thought of sleep in terms of inactivity. They theorized that sleep increased probability of survival by being inactive at certain times to not attract certain threats and conservation of energy. These functions allowed us to better survive with rest when threat is low, and to be efficient when we need to hunt for food or avoid predators. However, as we learn more about what happens to our bodies as we sleep, researchers have shown that the body is anything but inactive during sleep.
Restorative functions of sleep focus on the physical and cognitive healing that happens during sleep. Sleep promotes muscle growth and repairs tissues. Cognitively, sleep facilitates brain plasticity, the ability of the brain to digest information and learning. Also, sleep facilitates waste management for the brain. During sleep, our body naturally flushes out toxins.
Toxins and the Glymphatic System
The brain makes up 2% of body mass, but uses 20% of our body’s total energy. Neurons consume high amounts of energy and give out waste. This toxic waste is linked to Alzheimer’s.
The glymphatic system flushes out these toxins during sleep. Glymphatic vessels or channels acts as a drainage system for our brains, disposing of elements we don’t need.
The glymphatic system is a drainage system that mingles “fresh” cerebrospinal fluid (CSF) with waste product–rich brain interstitial fluid (ISF) and flushes the fluid and waste products out of the brain and into the systemic circulation.Does Sleep Flush Wastes From the Brain? | Anthony L. Komaroff, MD | JAMA Network
Certain habits can compromise the glympathic system such as chronic sleep loss, inactive lifestyle, and circadian misalignment. Aging also reduces glymphatic function.