Exercise is proven to help prevent depression. But the issue of how much exercise is needed…and how intense that exercise must be…has not been very clear. Now, there’s research that helps answer both these questions—and it could help you (and millions of others) be protected from depression’s heavy burden.

Are you getting enough exercise to ward off depression?

Background: Exercise is a powerful and well-established short-term mood booster. And decades of studies have found that getting regular activity is one of the most effective and reliable ways to treat clinical depression. But research on exercise to prevent depression in healthy people has been more mixed. Many studies have lumped together depression with anxiety, but they are different disorders. Nor has there been good evidence to identify the optimal duration or intensity needed to prevent the onset of depression.

Study: An international team of researchers led by the Black Dog Institute, a nonprofit mental health organization in Australia, analyzed the exercise levels and the symptoms of depression and anxiety in about 34,000 mentally and physically healthy Norwegian adults (average age 45) over a span of 11 years. This work is part of one of the largest and longest health studies ever conducted. At the beginning of the study, the participants were asked to report how often they exercised and how hard they worked out—for example, without becoming breathless or sweating…to the point of becoming breathless and sweating…or to exhaustion. At the end of the study, participants completed a questionnaire designed to identify signs of depression or anxiety.

Results: Not exercising at all was the big depression risk—people who didn’t exercise had a 44% increased chance of becoming depressed over 11 years compared with those who exercised just an hour or two per week. Then the researchers delved deeper into the duration question. It turned out that there was no additional benefit to exercising two hours per week compared with one. Nor was there any benefit to intensity such as breaking a sweat. In short, just one hour a week of moderate-intensity exercise, the kind you can get by walking or with easy biking, was enough to significantly reduce the risk of becoming depressed.

The findings were the same regardless of a range of variables—age (under age 50 or over age 50), gender, socioeconomic and demographic factors, use of alcohol or other substances, body mass index, physical health and social support.

Put another way, according to the researchers, 12% of depression cases could have been prevented with just one hour of moderate physical activity once per week. While the study couldn’t pinpoint how exercise protects, they believe that it’s a combination of physical effects on the brain, such as stimulating serotonin levels and brain-protective chemicals such as brain-derived neurotrophic factor, psychological benefits such as increased self-esteem and general improvements in physical health.

Surprising finding: Despite the significant effect exercise had on the risk for depression, it had no effect on preventing anxiety. That is, people who exercised a little, a moderate amount or a lot were all about as likely to experience an anxiety disorder. (Editor’s note: While exercise levels may not affect overall risk, other studies have found that a single bout of aerobic exercise, such as going for a run, can help reduce acute episodes of anxiety.)

Bottom Line: Getting people who are sedentary to become moderately active just an hour or more a week could be one of the most effective ways to reduce the burden of depression in society…and if you are sedentary, it could be one of the most effective ways for you to shield yourself from the onset of depression.

To be clear, though, that’s not enough exercise for optimal health. To protect your heart and help prevent other chronic ills, aim for 150 minutes of moderately intense exercise a week, or 75 minutes of intense exercise a week, or a combination of the two.

But it does underscore the good news that it doesn’t take superintense or superlong workouts to get the mood-stabilizing benefits of regular activity. Virtually anyone should be able to incorporate enough activity in their weekly schedule to potentially ward off depression. In other words, beating the blues may be, literally, a walk in the park.

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