How "brain cleaning" during sleep may reduce dementia risk

 

The glymphatic system, the brain's waste disposal mechanism, is believed to be more active while we sleep.

However, sleep disturbances may interfere with this waste disposal system and impede the brain's removal of poisons or waste products. Additionally, scientists are suggesting that an accumulation of these poisons brought on by sleep deprivation may raise a person's risk of dementia.
Since the majority of the research has been done on mice, there is still some disagreement regarding how this glymphatic system functions in humans.

However, it suggests that getting more sleep could increase the body's ability to eliminate these toxins from the brain, lowering the chance of dementia.

Here is what we currently understand about this new field of study.

The importance of waste

Waste is produced by every cell in the body. Through a network of lymphatic capillaries, the lymphatic system transports this waste from the voids between cells to the blood outside the brain.

However, there are no lymphatic vessels in the brain. And it was a mystery how the brain gets rid of its waste until approximately 12 years ago. At that point, researchers identified the "glymphatic system" and explained how it "flushes out" toxins from the brain.

The fluid that envelops the brain and spinal cord is called cerebrospinal fluid, and let us start with it. This fluid circulates in the vicinity of the blood arteries in the brain. After gathering waste in the voids between brain cells, it exits the brain through sizable veins that drain.

Researchers subsequently demonstrated in mice that this lymphatic system was at its peak during sleep, clearing out more waste.

Amyloid beta (Aβ) protein is one example of such a waste product. Plaques are clusters of Aβ that can form in the brain. Alzheimer's disease, the most prevalent form of dementia, is characterized by these and tau protein tangles in neurons, or brain cells.

Studies on mice and humans have revealed that levels of Aβ in the CSF fluid rise while the subjects are awake and then sharply decline while they are asleep.

However, a more recent study (in mice) revealed just the reverse, indicating that the glymphatic system is more active during the day. Scientists are arguing over possible explanations for the results.

Therefore, there is still more study to be done before we can precisely describe how the lymphatic system functions in both humans and mice to rid the brain of toxins that could otherwise raise the risk of dementia.

Does this also occur in humans?

We are aware that getting enough sleep is beneficial to our health, especially to our brains. We all know that sleep enhances memory and that sleep deprivation has short-term negative impacts on brain function.

In one study, healthy persons who experienced a single night of total sleep deprivation had higher levels of Aβ in the hippocampus, a region of the brain linked to Alzheimer's disease. This supports the notion that the human glymphatic system is more active during sleep and implies that sleep may affect the removal of Aβ from the brain.

This also begs the issue of whether getting enough sleep could improve the brain's ability to eliminate poisons like Aβ, making it a possible target for dementia prevention.

What about insomnia or sleep apnea?

Less is known about the effects of chronic sleep disturbances, such as those caused by sleep disorders, on the body's capacity to remove Aβ from the brain.

A common sleep disorder known as sleep apnea occurs when a person's breathing repeatedly pauses while they are asleep. Reduced blood oxygen levels and chronic (long-term) sleep deprivation may result from this. Both could have a role in the buildup of poisons in the brain.
Therefore, once more, it is too soon to conclude that treating a sleep issue lowers your risk of dementia because it lowers the amount of toxins in your brain.

A higher risk of dementia has also been connected to sleep apnea. Additionally, we now know that more Aβ is removed from the brain following treatment for sleep apnea.

Having trouble getting asleep and/or staying asleep is known as insomnia. There is also a higher chance of dementia if this persists over time. The impact of treating sleeplessness on chemicals linked to dementia is unknown, though.

What does this leave us with, then?

All of these research point to the need of getting enough good-quality sleep for a healthy brain, especially for the removal of chemicals linked to dementia.

However, it is yet unclear if treating sleep disorders or enhancing sleep in general has an impact on the brain's capacity to eliminate toxins and whether this lowers the risk of dementia. We and other researchers are actively researching in this field.

To better understand how sleep apnea impacts brain cleaning, for example, we are examining blood levels of tau and Aβ during the 24-hour sleep-wake cycle in individuals with sleep apnea, both on and off therapy.

To find out if this influences the removal of Aβ from the brain, researchers are also investigating the possibility of treating insomnia with a class of medications called orexin receptor antagonists.