Your Brain Flushes Out Waste Every Night... Here's How To Help It Clean Up

Authored by Flora Zhao via The Epoch Times (emphasis ours),

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 in time, we feel it. The signs can range from feeling foggy and fatigued to experiencing cognitive impairment.

Fortunately, efforts can be made to optimize waste clearance during the night.

Flush the Waste

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 byproducts, 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 brain. 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, with cerebrospinal fluid flowing through the space between the artery 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.

Deep Sleep

“Waste-removing processes in the brain barely operate during wakefulness. It is very much a process that occurs in our deep-sleep stages,” Moira Junge, who holds a doctorate in health psychology and is the CEO of the Sleep Health Foundation in Australia and an adjunct clinical associate professor at Monash University, told The Epoch Times.

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.

“It’s such a deep sleep that you’re not easily disturbed by the external environment; for example, you don’t hear the dog barking outside nor hear your partner come to bed,” Junge said.

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.

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 to the awake state.

Accumulated Beta-Amyloid

Unfortunately, Americans today are sleeping less than ever.

In 2023, 42 percent of Americans perceive that they get enough sleep, according to Gallup’s December 2023 poll. One in five people sleep fewer than five hours a night—compared to just 3 percent in 1942.

Shorter sleep duration can also be attributed to people going to bed increasingly later. One study found that delaying bedtime by just one hour reduces total sleep by 14 to 33 minutes each night.

In addition to going to bed later and sleeping less, we are also not sleeping well. According to the American Psychiatric Association, more than 50 million people in the United States suffer from chronic sleep disorders like insomnia and sleep apnea.

These issues directly reduce and disrupt deep sleep, shortening the critical window during which the glymphatic system works at peak efficiency. This, in turn, leads to greater waste accumulation in the brain.

People reporting less adequate sleep and more sleep problems had greater amyloid burden in Alzheimer’s disease-sensitive brain regions.

A 2021 human study found that even a single night of sleep deprivation can impair the brain’s ability to clear waste.

An earlier clinical trial showed that despite the expected relatively sizeable interindividual variation in levels of a type of amyloid-beta, the average beta-amyloid accumulation from three morning samples of unrestricted sleep was 6 percent lower than that of three evening samples.

In comparison, participants who stayed awake for 24 hours exhibited amyloid-beta levels up to 75.8 picograms per milliliter higher. This demonstrated that unrestricted sleep reduced amyloid-beta proteins but that sleep deprivation counteracted this effect. Furthermore, the longer the sleep duration—provided it was not excessive—the greater the reduction in beta-amyloid biomarkers.

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