Sleep to Clean Your Brain and Prevent Neurodegeneration

The concept of brainwashing usually brings up images of some evil genius altering and controlling the minds of humans. However, brainwashing in its literal sense actually happens every night when you sleep.

Brainwashing, more scientifically known as brain waste clearance, is a process during which harmful waste products, so called “biological trash”, is removed from your brain. This is crucial for optimal brain functioning and to lower the risk of neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease and dementia, which are associated with buildup of such harmful waste products. Only recently scientists discovered that your brain is cleaned only when you are sleeping.

Waste products build up in the body and brain throughout the day

First you might be wondering what needs to be cleaned and removed here? What is “biological trash”?

Throughout the day all cells in our body produce leftover molecules and metabolites due to cellular activity. There is also cellular debris and other harmful toxic molecules that get into our body from the surrounding environment. Moreover, due to various internal and external factors such as our genetic predispositions and UV exposure, certain proteins in our body might change their structure, lose their normal function and become harmful. All of these molecules need to be removed from our body to avoid health problems and disease.

Brain has a different system to clean waste products than the rest of the body

Our body has a wonderful “cleaning system” that removes such “biological trash” and detoxifies our tissues, called the lymphatic system. It consists of specific lymphoid organs, such as thymus, bone marrow and lymph nodes, lymphatic vessels and a fluid called lymph that circulates throughout our body and removes excess fluid and waste products.

However, not even a single trace of the lymphatic system is detected inside our brain. This is rather surprising as the brain is the most active organ of our entire body and therefore is likely to produce most waste products. In 2012 a groundbreaking study was published which showed that our brain has a different kind of waste clearance system than the rest of the body.

The study described the anatomical pathways and the working principle of the brains’ waste disposal system, which was given the name of the glymphatic system. Apparently, the brain uses a system of tunnels that are formed around the brain's blood vessels by special brain cells called the astrocytes. Astrocytes belong to a group of so-called glial cells, hence the name glial + lymphatic = glymphatic. A special brain fluid called the cerebrospinal fluid flows in these tunnels and then through our brain, collecting waste from around the brain cells and then draining it out of the brain and out of our body.

Brains’ waste disposal system is ON when we sleep

Another groundbreaking study was released just a year later in 2013 which showed that waste products from the brain are removed almost only during sleep. Scientists injected a green dye into the brain of mice after which half of the mice went to sleep and the other half stayed awake. After two hours scientists checked how much of the green dye was left in the brains of these mice.

Surprisingly, brains of mice which stayed awake were still full of the green dye, while the brains of the ones that slept barely had any trace of green dye. These results indicated that substances are removed from the brain much faster during sleep when compared to being awake.

Now many studies in various animal species including humans support the finding that our brains are cleaned from harmful molecules almost exclusively during sleep. For example, a 2018 study with 20 healthy adults showed that a single night of no sleep is associated with significant increase in levels of a specific brain waste product, a protein called amyloid-beta.

A 2021 study investigated how well an externally delivered molecule is cleaned from the brain if you sleep compared to if you don’t sleep. Scientists delivered a special molecule called contrast agent into the brains of patients. Half of them were allowed to sleep and half were asked to spend one night not sleeping. When scientists scanned the brains of these 2 groups of patients, they found higher levels of the contrast agent in the no-sleep group compared to the group that slept. This means that even one night of sleep deprivation impairs brain waste clearance.

Too little sleep increases the risk of neurodegenerative diseases

Build-up of certain waste products in the brain is associated with increased risk of neurodegenerative diseases, such as Alzheimer’s, Parkinson’s diseases and dementia. Now we know that our brain is cleaned and waste products removed when we are sleeping. This would mean that if we don’t get enough sleep, we expose ourselves to higher chances of neurodegenerative diseases.

For example, one study examined nearly 8000 people and found that people who slept six hours or less per night in their 50s and 60s were 30% more likely to develop dementia later in life compared to those who slept 7 hours or more every night.

Another study investigated nearly 700 individuals who due to their genetic make-up were at risk of developing Alzheimer’s disease. Researchers found that better sleep reduced the likelihood of developing clinical Alzheimer’s disease and even reduced the amount of harmful proteins in the brain.

A recent 2020 study showed that sleep disturbances early on can even forecast how much of the harmful protein amyloid-beta will accumulate in a person's brain. The worse people sleep, the more likely they are to end up having larger amounts of amyloid-beta in their brain which is known to increase the risk of neurodegenerative diseases.

The build-up of waste products in our tissues is a physiological process that happens due to cellular activity. As long as these waste products are efficiently removed, we should not worry. Now we know that our brain has a different kind of waste disposal system than the rest of our body, which interestingly is ON only when we sleep. Therefore, make sure to get enough sleep every night to keep your brains “clean” (literally), and to reduce your risk of developing neurodegenerative diseases!