Exactly why exercise is so good for brain health and how much you need to do

A good night’s sleep has long been regarded as a cure for all ailments, especially in clearing harmful toxins from the brain.

Neuroscientists have long believed that deep sleep helps clear problematic debris from the brain, flushing out many of the proteins and metabolites thought to be involved in brain development. Alzheimer’s and other dementias.

This is hardly reassuring for the insomniacs among us. Definitive proof has always been difficult to come by, however, and a new study in the journal Nature Neuroscience Cold water has been poured on the theory. Although sleep is still crucial for many aspects of health, Bill Wisden, a professor at the UK’s Dementia Research Institute who co-led the study, says that being active may play a much bigger role in the clearance of toxins.

“We have shown that brain clearance is very effective during the waking state,” he says. “In general, being awake, active and exercising may clear the brain of toxins more effectively.”

This is undoubtedly good news for anyone struggling to get 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 recommendation comes with a growing body of research advances in recent years that point to the importance of exercise for all aspects of the brain.

Clearance of toxins

Exercise’s role in removing waste from the brain is an active area of ‚Äč‚Äčinvestigation in research laboratories around the globe. The working theory involves brain cells that shift certain shapes called microglial cells that can take on different personalities depending on your health.

In some psychiatric conditions such as schizophrenia and even Long Covid, the disease process causes the microglia to take a conspicuously spiky form, generating inflammation and disrupting the natural functioning of the brain.

However, researchers suspect that exercise may actively stimulate microglia to adopt a healthier anti-inflammatory shape. This means that they would act as helpful scavengers, cleaning up detritus and ensuring that the synaptic connections between neurons are clean and functioning properly.

“Microglia are there to survey everything,” says Dr. Rebecca MacPherson, an associate professor at Brock University in Canada where she runs a lab studying how exercise benefits the brain. “We’re investigating this idea that exercise activates them in a way that improves the way they clear metabolic products.”

The brain fertilizer

Repeated research shows that the risk of all forms of dementia is reduced by 28%, and Alzheimer’s disease in particular by 45%.

Over the years scientists have conducted various experiments where the participants were randomized into two different groups, with one group following an exercise program and the other remaining sedentary. Almost all of them reported that the exercise program group did 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 related to a molecule called brain-derived neurotrophic factor or BDNF. This molecule has gained a reputation among neurologists as ‘brain fertilizer’ for its amazing ability to stimulate the growth of new neurons and strengthen the connections between them.

“Muscle contractions increase BDNF and your platelets in the blood store a lot of BDNF,” says MacPherson. “So because of increased blood flow due to exercise, your platelets can release more of it into the circulation.”

Through studies on cells and animals, MacPherson’s lab has even shown that BDNF prevents the accumulation of tiny amyloid beta protein fragments in the brain by changing the activity of various enzymes, which may explain why exercise helps to reduce Alzheimer’s risk.

But BDNF isn’t the only beneficial molecule released when you exercise. Last year, a study in the journal Neurons showed that exercise causes the production of a hormone called irisin that can clear amyloid plaques.

Christiane Wrann, assistant professor of medicine at Harvard Medical School, who was involved in the study, was so interested in irisin that she is now trying to develop an artificial form of it as a therapeutic for various neurodegenerative diseases including Alzheimer’s and Parkinson’s.

“It’s a small hormone that works on neuroinflammation and plaque clearing which makes it very relevant to Alzheimer’s disease,” she says. “I think irisin has three or four properties that make it a very promising drug target.”

How much exercise and what intensity is best?

MacPherson gives a smile when this question is broken. “Everybody wants to know exactly what to do, and that’s a difficult question to answer,” she says.

NHS guidelines advise you to do some form of aerobic exercise, or physical activity that gets your heart rate up, for at least 30 minutes a day, five days a week.

McPherson says there is a correlation between BDNF production and exercise intensity, so your body will produce more when you do more intense types of activity, such as interval training. However, she says it’s important for people to do what they can, and that any form of exercise, no matter how light, will have some benefit for the body and the brain.

“I think as an individual, you have to think, how much time do I have and what do I enjoy?” she says. “Even if you’re only able to do moderate intensity exercise, you still get an increase in BDNF, and the increased blood flow delivers more oxygen and nutrients to the brain which will also promote brain cell growth.”

The scientific reason exercise boosts your mood

Exercise is also known to have the ability to provide relief for people struggling with symptoms of depression, such as low mood or anhedonia, which refers to the loss of pleasure in previously rewarding activities.

At University College London, cognitive neuroscientist Professor Jonathan Roiser is leading a Wellcome-funded clinical trial to try to understand more why exercise is so beneficial for mental health.

“I have long been interested in the aspects of information processing that go wrong in depression and how they contribute to symptoms,” he says. “There are other symptoms that tend to cluster together with anhedonia such as fatigue and difficulty making decisions, and there are some clues that exercise is specifically targeting these symptoms.”

Roiser’s trial will examine the greater benefits of aerobic exercise, where participants get out of breath and break a sweat, compared to light stretching and rest, in people with depression.

The aim is to find further proof of some of the major theories behind how exercise benefits mental health, such as stimulating the production of dopamine, which is associated with motivation, as well as reducing inflammation.

“Many people with depression experience what we call chronic inflammation that prevents dopamine neurons from firing and may contribute to their symptoms,” he says. “So the anti-inflammatory effects of exercise are a key part of how we think it works.”

As we learn more and more about how exercise protects the body, it may even lead to a new class of drugs called exercise mimetics that could mimic some of the benefits of physical activity. provision for the disabled and weak.

But for the rest of us, researchers have one simple message – whether it’s the gym or playing sports, taking time to stay active will keep your mind healthier 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.

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