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Your brain flushes out toxins – if you sleep properly, that is

Sleep research — Your brain cleans itself of waste products during deep sleep. A new study from the University of Copenhagen sheds more light on a good night.

We all do it. Some more than others, and some better than others. We all need sleep to cleanse our brains of waste products. The driving force behind this cleansing system was previously unknown, but now a new study from the University of Copenhagen (UCPH) has identified the underlying mechanism: It is the neurotransmitter called noradrenaline that takes care of things.

The University Post spoke to Natalie Hauglund who is lead researcher on the study and a postdoc at the Center for Translational Neuromedicine at UCPH and at the University of Oxford. We wanted to understand what the discovery means, and how it impacts those valuable hours of sleep.

The glymphatic what?

The brain’s waste clearance system is called the glymphatic system. Think of it as the brain’s washing machine. Cerebrospinal fluid flows through the brain, flushing out waste products. And the engine behind this process is the release of noradrenaline.

»When we sleep, the neurotransmitter noradrenaline is released in the brain at intervals of about 50 seconds. The substance binds to blood vessels, causing them to contract. This rhythmic expansion and contraction of the blood vessels acts like a pump, driving the cerebrospinal fluid in and out of the brain,« explains Natalie Hauglund.

Why waste products need to be removed

During the course of the day, waste products accumulate, and getting rid of them is crucial to brain health. A consequence of excessive waste accumulation is for example neurodegenerative diseases like Alzheimer’s.

Stress, screen time, and excessive light before bedtime impair sleep

Natalie Hauglund, postdoc at the Center for Translational Neuromedicine

»Many brain diseases are associated with waste accumulation in the brain. For example, we see a link between Alzheimer’s and the build-up of beta-amyloid plaques, which suggests that they have not been properly cleared out,« says Natalie Hauglund.

Furthermore, it is essential to allow the brain time to go offline to maintain crucial functions such as memory, learning, concentration, and the immune system, she explains, emphasizing:

»Sleep is incredibly important for all these functions.«

The same neurotransmitter for stress and sleep

Students, stress, and sleep

UCPH’s latest student well-being survey from 2023 shows that students experience significant pressure, which can negatively affect sleep.

Nearly half (49%) report experiencing severe stress symptoms in daily life sometimes, often, or always. During exam periods, this rises to two-thirds of the students (66%).

Almost a third of students (31%) say they do not have a good balance between study time and free time.

Noradrenaline has long been known as a stress response hormone that prepares the body for fight or flight situations. When the body is in a high-alert state, it releases large amounts of noradrenaline. A good night’s sleep, however, requires the right balance between high and low levels of the neurotransmitter.

»When we are awake, noradrenaline levels are very high. When we fall asleep, they decrease, and the slow rhythmic release activates the pump that drives cerebrospinal fluid through the brain. Other studies on sleeping mice have shown that when the mice are stressed, the noradrenaline waves are much faster, causing them to wake up more frequently and get poorer sleep,« says Natalie Hauglund.

What about sleeping pills?

A new study from the Danish Health Authority recommends that adults aged 18 to 64 get seven to nine hours of sleep with regular sleep and wake times. The same study shows that two-thirds of all adults do not get enough sleep.

Many brain diseases are associated with waste accumulation in the brain

Natalie Hauglund, postdoc at the Center for Translational Neuromedicine

The findings of the new UCPH study are an important step toward understanding how sleep problems can be reduced, says Natalie Hauglund:

»Now we can consider more factors than just whether someone appears to have good sleep. Doctors can start investigating how well the blood vessels perform this pump function. For instance, we know that blood vessels become stiffer with age.«

She continues:

»Our findings may hopefully contribute to the development of tailored medications in the long run. To stimulate the cleansing process, the goal would be to enhance the blood vessels’ ability to pump cerebrospinal fluid if the pump is not working optimally.«

With increasing sleep problems, many may be tempted to turn to sleeping pills. However, the new study has found a surprising link between noradrenaline release and the prescription sleep medication Zolpidem:

»We discovered that the sleeping pill Zolpidem lowered noradrenaline levels to the point where we no longer saw these cleansing waves. Our results suggest that the sleep induced by sleeping pills is not as beneficial as natural sleep,« says Natalie Hauglund.

Help, I sleep poorly

As of now, there is no medical miracle cure if you dream of waking up like Cinderella in the Disney movie: well-rested, full of energy, and to the sound of birdsong. But there are things you can do to improve your sleep.

The sleep you get on sleeping pills is not as good

Natalie Hauglund, postdoc at the Center for Translational Neuromedicine

According to Natalie Hauglund, it is not possible to directly influence noradrenaline release to improve brain cleansing. However, we do know that the brain’s washing machine functions during deep sleep. By creating optimal conditions for this sleep stage, we can indirectly enhance the cleansing process and improve sleep quality.

»It is during non-REM sleep, the deep sleep phase, that we see these slow cleansing waves in the brain. During REM sleep, which is still important for many other functions, noradrenaline is not released at all,« she says.

This means we must continue to improve our habits to support deep, restorative sleep:

»Factors such as stress, screen use, and excessive light exposure before bedtime reduce sleep quality and impair the brain’s ability to carry out the cleansing process,« says Natalie Hauglund.

In other words, conventional sleep advice remains the best approach. Prioritise sleep, avoid screens and doomscrolling before bed. Yes, this might set off a yawn! But that’s the point.

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