Exercise boosts the brain — and mental health

Diana J. Smith

It’s hardly news that exercise is good for your physical health, and has long been extolled as beneficial for mental health, as well. But researchers are now making progress in understanding how exercise works its mental magic.

Exercise, they are learning, has profound effects on the brain’s structure itself, and it also provides other, more subtle benefits such as focus, a sense of accomplishment and sometimes social stimulation — all of which are therapeutic in their own right. And while more is generally better, even modest levels of physical activity, such as a daily walk, can pay big dividends for mental health.

“It’s a very potent intervention to be physically active,” says Anders Hovland, a clinical psychologist at the University of Bergen in Norway.

But that knowledge has barely begun to percolate into practice, says Joseph Firth, a mental health researcher at the University of Manchester in the United Kingdom. Just ask a hundred people receiving mental health care how many are getting exercise prescriptions as part of that care. “You wouldn’t find many,” Firth says.

A tool against depression

Some of the strongest evidence for the mental benefits of exercise centers on depression. In 2016, Hovland and his colleagues searched the published literature and identified 23 clinical trials that tested the effectiveness of exercise in treating depression. Exercise was clearly effective and, in a few studies, on par with antidepressant drugs, the researchers concluded.

And exercise offers several advantages. For one thing, antidepressant medications generally take several weeks to show their full effect. Exercise can improve mood almost immediately, making it a valuable supplement to front-line treatments such as drugs or therapy, says Brett Gordon, an exercise psychology researcher at the Penn State College of Medicine. Plus, he says, exercise can counteract some of the unpleasant side effects of antidepressants, such as weight gain.

In addition, exercise has few of the negative side effects common with drugs. “Many people who have mental health concerns are not enthusiastic about starting a medication for the rest of their lives, and are interested in pursuing other options. Exercise might be one of those options,” says Jacob Meyer, an exercise psychologist at Iowa State University.

But researchers are still figuring out how muscular exertion acts on the brain to improve mental health. For most biomedical questions like this, the first stop is animal experiments, but they aren’t as useful in studies of mental health issues.

“Psychological health is so uniquely human that it can be hard to make a good jump from animal models,” Meyer says.

Just scratching the surface

Scientists have some ideas how exercise enhances mental health, says Patrick J. Smith, a psychologist and biostatistician at Duke University Medical Center in North Carolina, who wrote about the subject in the 2021 Annual Review of Medicine with Duke colleague Rhonda M. Merwin.

It doesn’t seem to have much to do with cardiovascular fitness or muscular strength — the most obvious benefits of exercise. Something else must be going on that’s more important than mere fitness, Smith says.

One possibility is that exercise buffs up the brain as well as the body. Physical exercise triggers the release of a protein known as brain-derived neurotrophic factor (BDNF). BDNF encourages the growth of new brain cells — including, possibly, in the hippocampus, a brain region important in memory and learning. Since the hippocampus tends to be smaller or distorted in people with depression, anxiety and schizophrenia, boosting BDNF through exercise may be one way physical activity might help manage these conditions.

Sure enough, studies show that people with depression have lower levels of BDNF — and, notably, one effect of some antidepressants is to increase production of that molecule. Researchers have not yet shown directly that the exercise-associated increase in BDNF is what reduces depressive symptoms, but it’s a promising possibility, Hovland says.

Exercise may also help anxiety disorders. The brain changes prompted by BDNF appear to enhance learning, an important part of some anti-anxiety therapies — so it’s possible that exercise may improve the effectiveness of such therapies. One PTSD therapy, for example, involves exposing patients to the fear-causing stimulus in a safe environment, so that the patients learn to recalibrate their reactions to trauma-linked cues — and the better they learn, the more durable this response might be.

Kevin Crombie, an exercise neuroscientist at the University of Texas at Austin, and colleagues tested this idea with 35 women with PTSD. After being taught to associate a particular geometric shape with a mild electric shock, the volunteers repeatedly saw the same shape without the shock to learn that the stimulus was now safe. A few minutes later, half the volunteers did 30 minutes of jogging or uphill walking on a treadmill, while the other half did only light movement.

Exercise also stimulates the release of endocannabinoids, molecules important in modifying connections between brain cells. This may provide another way of enhancing the learning that underlies successful treatment for depression, PTSD and other mental disorders.

Physical activity also moderates the body’s response to stress and reduces inflammation, plausibly helping people with mental illness. “We have just scratched the surface,” Hovland says.

Changing the structure of the brain isn’t the only way physical activity can be beneficial for mental health. The habit of exercise itself can help, Smith says.

For people with mental health issues, simply doing something — anything — can occupy their attention and keep them from ruminating on their condition. One survey of the published literature found that placebo exercise — that is, gentle stretching, too mild to cause any physiological effect — had almost half the beneficial effect on mental health as strenuous exercise did.

Regular workouts also give exercisers a clear sense of progress as their strength and fitness improves. This sense of accomplishment can help offset some of the burden of anxiety and depression, Gordon says.

Even light activity — basically just moving around now and then during the day instead of sitting for hours at a time — may help.

In one study of more than 4,000 adolescents in the U.K., Aaron Kandola, a psychiatric epidemiologist at the University College London, and his colleagues found that youths who undertook more light activity during the day had a lower risk of depressive symptoms than those who spent more time sitting.

Exercise has powerful benefits for people with mental illness that go beyond its effects on the illnesses themselves. Many struggle with related issues such as social withdrawal and a reduced capacity for pleasure, Firth says. Standard medications reduce some symptoms but do nothing to address these other problems. Exercise — especially as part of a group — can help boost their mood and enrich their lives.

Even more important, people with serious mental illnesses such as severe depression and schizophrenia also are more likely to have significant physical health issues such as obesity, heart disease and other chronic diseases. As a result, their life expectancy is 10 to 25 years lower than that of unaffected people.

“Reducing those health risks is really paramount at the moment,” Kandola says. “That’s the big appeal of exercise: We already know it can improve physical health. If it does have mental health benefits as well, it can be quite an important addition to treatment.”

Bob Holmes is a science writer who lives and exercises in Edmonton, Alberta.This article originally appeared in Knowable Magazine, an independent journalistic endeavor from Annual Reviews.

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