A satisfying night’s sleep has long been branded as the cure for all ailments, especially when it comes to removing harmful toxins from the brain.
Neuroscientists have long believed that deep sleep helps clear problematic waste from the brain, flushing out many of the proteins and metabolites thought to be involved in the development of brain hemorrhages. Alzheimer’s and other forms of dementia.
This is not exactly reassuring for the insomniacs among us. But definitive proof has always been difficult to come by, and a new study in the journal Nature Neuroscience has poured cold water on the theory. While sleep is still vital for many aspects of health, Bill Wisden, a professor at the UK Dementia Research Institute who was involved in leading the study, says being active may play a much bigger role in elimination of toxins.
“We have shown that brain clearance is very efficient during the waking state,” he says. “In general, being awake, active and exercising can cleanse the brain of toxins more efficiently.”
This is undoubtedly good news for anyone who struggles to manage seven hours a night. After all, a brisk half-hour walk is something most of us can manage even after a night of tossing and turning.
Wisden’s suggestion joins a growing number of research breakthroughs in recent years that point to the enormous importance of exercise for all aspects of the brain.
Clearance of toxins
The role of exercise in removing waste from the brain is currently an area of active research in research laboratories around the world. The working theory involves certain shape-shifting brain cells known as microglial cells, which can take on different personas depending on your health status.
In some psychiatric conditions, such as schizophrenia and even Long Covid, the disease process causes microglia to take on a visibly spiky shape, causing inflammation and disrupting the brain’s natural functioning.
However, researchers suspect that exercise may actively cause microglia to adopt a healthier anti-inflammatory guise. This means that they would act as helpful scavengers, cleaning up waste and ensuring that the synaptic connections between neurons are clean and functioning properly.
“Microglia are there to map everything,” says Dr. Rebecca MacPherson, an associate professor at Brock University in Canada, where she runs a lab that studies how exercise benefits the brain. “We’re exploring this idea that exercise activates them in a way that improves the way they clear the products of metabolism.”
The brain fertilizer
Research has repeatedly shown that being physically active reduces the risk of all forms of dementia by 28%, and Alzheimer’s disease in particular by 45%.
Over the years, scientists have conducted several experiments in which participants were randomly divided into two different groups, with one group following an exercise program and the other remaining sedentary. Nearly all reported that the exercise program group performed better on cognitive tests, with the same trend found in healthy participants, stroke survivors and even Alzheimer’s patients.
Much of this is thought to be due to a molecule called brain-derived neurotrophic factor, or BDNF. This molecule has earned a reputation among neuroscientists as “the brain fertilizer” due to its remarkable ability to stimulate the growth of new neurons and strengthen the connections between them.
“Muscle contractions increase BDNF, while your platelets in the blood store a lot of BDNF,” says MacPherson. “So with increased blood flow due to exercise, your platelets can release more of them into the bloodstream.”
In fact, through studies conducted on cells and animals, MacPherson’s laboratory has shown that BDNF prevents the accumulation of small beta-amyloid protein fragments in the brain by altering the activity of several enzymes, which could explain why exercise increases the risk of Alzheimer’s disease helps reduce.
But BDNF isn’t the only beneficial molecule released when you exercise. Last year a study was published in the journal Neuron showed that exercise causes the production of a hormone called irisin, which is able to remove amyloid plaques.
Christiane Wrann, an assistant professor of medicine at Harvard Medical School who was involved in the research, is so fascinated by irisin that she now wants to develop an artificial form of it as a therapeutic agent for several neurodegenerative diseases, including Alzheimer’s and Parkinson’s.
“It’s a small hormone that works on neuroinflammation and plaque clearing, making it very relevant to Alzheimer’s disease,” she says. “I think irisin has three or four properties that make it a promising drug target.”
How much exercise and what intensity is best?
MacPherson smiles wryly when asked this question. “Everyone wants to know exactly what to do, and that’s difficult to answer,” she says.
The NHS guidelines recommend that you do some form of aerobic exercise, or physical activity that increases your heart rate, for at least 30 minutes a day, five days a week.
MacPherson says that BDNF production correlates with exercise intensity, so your body will produce more during higher-intensity forms of activity, such as interval training. However, she says it’s important that people do what they feel capable of, and that any form of exercise, no matter how mild, will still provide some benefit to the body and brain.
“I think as an individual you have to think: how much time do I have and what do I like?” she says. “Even if you can only do moderate intensity exercise, you’ll still get an increase in BDNF, and there’s also the increased blood flow that delivers more oxygen and nutrients to the brain, which will also improve brain cell growth.”
The scientific reason that exercise improves your mood
Exercise is also known to provide relief for people struggling with symptoms of depression, such as low mood or anhedonia, which refers to a loss of pleasure in previously rewarding activities.
At University College London, cognitive neuroscientist Professor Jonathan Roiser is currently leading a Wellcome-funded clinical trial to understand more about why exercise is so beneficial for mental health.
“I have long been interested in the information processing aspects that go wrong in depression and how these contribute to the symptoms,” he says. “There are other symptoms that often accompany anhedonia, such as fatigue and difficulty making decisions, and there is some evidence that exercise specifically targets these types of symptoms.”
Roiser’s trial will investigate the greater benefits of aerobic exercise, which leaves participants breathless and sweating, compared to mild stretching and relaxation exercises, in people with depression.
The aim is to gain further evidence for some of the main theories behind how exercise benefits mental health, such as boosting the production of dopamine, which is involved in motivation, and dampening inflammation.
“Many depressed people experience what we call chronic inflammation, which prevents dopamine neurons from firing and this may contribute to their symptoms,” he says. “So the anti-inflammatory effects of exercise are a core part of how we think it works.”
As we discover more and more about how exercise protects the body, this could even lead to a new class of drugs known as exercise mimetics, which could provide some of the benefits of physical activity to the disabled and vulnerable.
But for the rest of us, researchers have one simple message: whether it’s the gym or exercising, making time to stay active will keep your mind healthy for longer.
“Whether it’s improving mood or cognitive function, exercise is one of the best things you can do for your brain,” says Wrann.