We all know sleep is good for you, but did you know it cleanses your brain? This is actually new information, but increases the evidence that getting more sleep may help prevent dementia as well as fatigue.
Flora Zhao, writing in The Epoch Times, tells us “As we fall asleep, the brain begins clearing out waste. It operates like a late-night laundry service, with all the water valves opened and washing machines running at full capacity to remove dirt from piles of clothes, flushing the wastewater into the drain. The brain continuously produces various wastes, and if these are not cleared regularly, we feel it. The signs can range from feeling foggy and fatigued to experiencing cognitive impairment.”
The human brain is one of the most metabolically active organs, accounting for about 20 percent of the body’s total energy expenditure. This high level of activity generates significant waste. Smaller by-products, such as carbon dioxide, urea, and ammonia, diffuse into capillaries and are cleared through the bloodstream. Larger neurotoxic proteins—including beta-amyloid and tau, both widely associated with an increased risk of Alzheimer’s disease, cannot be eliminated through the bloodstream alone due to their size.
In the past it was believed that the brain lacked a lymphatic system to remove waste and relied solely on internal mechanisms for clearance. However, in 2012, researchers discovered a specialized mechanism within the brain, analogous to the lymphatic system and capable of flushing out larger waste products from deep within the organ. This system was named the glymphatic system, a portmanteau of “glial” (referring to glial cells) and “lymphatic.” It is also known as the pseudo-lymphatic system.
Surrounding the arteries in the brain is a sheath-like structure, and cerebrospinal fluid flows through the space between the arteries and this sheath. During sleep, the brain’s blood vessels constrict, increasing the space between the vessels and the sheath, which allows more cerebrospinal fluid to flow in. As the arteries pulse, the cerebrospinal fluid is pumped through brain tissue, flushing out waste—such as beta-amyloid and tau proteins—from the deeper spaces between brain cells, eventually clearing it from the brain.
Sleep is divided into two states: rapid eye movement (REM) sleep and nonrapid eye movement (NREM) sleep. NREM makes up 75 percent of total sleep time and is further divided into three stages, N1, N2, and N3—each reflecting progressively deeper levels of sleep. During N3, brainwaves are at their slowest. During sleep, the body moves through the stages sequentially, forming a complete sleep cycle lasting around 90 minutes. Throughout the night, a person typically experiences four to five sleep cycles.
The glymphatic system becomes more active during sleep, especially during deep sleep, allowing for more effective waste clearance, said psychiatrist Dr. Jingduan Yang, founder of the Yang Institute of Integrative Medicine in Pennsylvania and a contributor to The Epoch Times.
In a mouse study published in Science, researchers used tracers to monitor changes in cerebrospinal fluid flow. They found that during sleep, the interstitial, or intervening, space expanded by more than 60 percent, and the tracer influx increased. The brain’s clearance rate of beta-amyloid doubled during sleep (or under anesthesia) compared with the awake state.
(For more on this subject, see Part II of this series next post.)
