By Jamie Ducharme
January 25, 2019

Ask anyone who’s ever felt better after a workout, and they’ll tell you that exercise and mental health are related. Science backs up that gut feeling. Many studies have found that physical activity is linked to a lower risk of developing depression, and better outcomes for people who have it.

But does exercise actually prevent depression, or are people who don’t have depression simply more likely to be active?

A new study, published in JAMA Psychiatry, sheds some light on that question. Using genetic data from more than 600,000 adults enrolled in multiple genomic association studies, researchers found “more evidence than ever before that physical activity does play an important, and likely causal, role in reducing risk for depression,” says Karmel Choi, a clinical and research fellow in psychiatric and neurodevelopmental genetics at Massachusetts General Hospital and a co-author of the study.

The researchers looked at one or more of several different measures: people’s genomes, their medical histories of depression and depressive symptoms and how much physical activity they got (as measured by wearable fitness trackers and self reports). Comparing this information, they identified several gene variants linked to a person’s likelihood to exercise, and others associated with a person’s likelihood of developing depression.

People who had genetic markers linked to a greater likelihood of exercising were less likely to develop depression, but people with markers of depression were not less likely to exercise. This finding, they say, suggests that exercise can protect against depression, but depression does not inherently make someone less likely to exercise.

“Physical activity is good for a lot of things,” says co-author Dr. Jordan Smoller, director of the Psychiatric and Neurodevelopmental Genetics Unit at Massachusetts General Hospital. “It may have benefits not only for all kinds of aspects of your health, but also, it looks like, your risk of developing depression.”

The new research is only the latest study to say that exercise may prevent depression. Here’s what else the science says about how exercise affects mental health.

Exercise may improve depression treatment

Exercise is not a cure for mental health issues, and depression itself can be an obstacle to getting enough physical activity. (Despite the findings of the JAMA study, plenty of anecdotal evidence suggests that many people with depression do find it difficult to exercise, for reasons including antidepressant side effects like fatigue and weight gain, and how difficult it can be to find the energy to exercise.)

But while exercise is not a perfect solution for depression, studies have shown that it can make a difference. One 2018 review of studies found that physical activity — specifically resistance training, like weight-lifting — can reduce symptoms of depression, perhaps even as effectively as conventional treatments like cognitive behavioral therapy and medication for some people. Other studies have found that virtually any type of workout, from cardio to yoga, can lessen depressive symptoms.

It’s still unclear how exercise may achieve these effects, but researchers have theories. Rigorous workouts, like weight-lifting and running, may increase blood flow to the brain, potentially altering its structure and cellular makeup. Exercise can also trigger the release of mood-boosting endorphins. Yoga’s emphasis on breath work and mindfulness may also play a part.

You don’t have to exercise a lot to see a difference

Research is finding that even small amounts of exercise improve both physical and mental health. “If instead of sitting down for 15 minutes you ran for 15 minutes, or if instead of sitting down for an hour you walked briskly for an hour, that’s the level of activity that might actually make a difference,” says Stoller, co-author of the new JAMA study.

Using data from more than 1.2 million U.S. adults, a large study from 2018 found that people could achieve better mental wellbeing by doing as little as two hours of exercise each week (about 20 minutes per day). It even said that doing too much exercise — more than six hours per week — may backfire psychologically. One study from 2017 came to an even more doable conclusion: that just an hour of exercise a week may be enough to prevent depression.

Your workout doesn’t have to be brutal

Finding the motivation to exercise can be easier if you expand the definition of what it means to be active.

Choi, the JAMA study co-author, says that even “things like taking the stairs, or walking to the store, or washing dishes, or putting away laundry” — which people might not view as exercise — “could add up together to have beneficial effects on depression.”

In a 2017 study, light exercise like walking was actually more beneficial to mental health than vigorous exercise. The recently updated federal physical activity guidelines also say that all types of movement can contribute to meaningful physical and mental health benefits, even if they’re accumulated in tiny chunks.

If getting to the gym feels like a herculean task, start small. Even a short walk can put you on the path to better mental health.

Write to Jamie Ducharme at jamie.ducharme@time.com.

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