Even a little exercise seems to prevent depression

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This month’s research points to a mental health benefit of regular exercise. The review found that people who reported being physically active were less likely to be diagnosed with depression later on. This association was most apparent in people who seemed to meet the recommended amount of exercise per week, but could still be seen in people who exercised half as much.

Exercise is one of the healthiest things a person can do, and many studies in recent years have found which can keep the body and brain fit. I know knows that physical activity also helps people with acute mental health problems, along with other treatments. But this new research, published in JAMA Psychiatry this April, attempts to quantify the protective effect that different levels of exercise may have in preventing depression.

The study reviewed data from 15 population studies, involving almost 200,000 people. It is important to note that it was prospective studies, meaning that people’s health outcomes were intentionally tracked from the start; in contrast, a retrospective study can only go back in time, making it difficult to confirm a cause-and-effect link between a factor and a health outcome. As part of these reviewed studies, participants were asked about their level of physical activity and their history of clinical depression was also recorded.

Compared with people who didn’t report being physically active, people who reported being physically active had a significantly lower risk of depression, the study found. More specifically, people who met the minimum duration of exercise recommended by many public health organizations, roughly the equivalent of two and a half hours of brisk walking per week, had a 25% lower risk of depression. But those who exercised half as much still had an 18% lower risk, while only “minor additional benefits” were seen in people who exercised more. Based on their model, they also estimated that if less active people were able to meet the recommended level of physical activity, up to 11% of future cases of depression would be avoided.

The authors note that their work may overestimate the effect of exercise on depression risk. One possibility, for example, is that people who were depressed but had not yet been diagnosed at the start of the study would also be less likely to exercise. To help mitigate this potential problem, they only looked at studies with longer follow-up times (at least three years), but noted that some bias may still exist. And the authors call for more studies that can better rule out any confounding and reinforce a causal link between exercise and depression prevention.

That said, many studies have found that exercise can have direct and indirect effects in the well-being of people and in the risk factors for depression, from the mood boost that people feel while exercising (the well-known runner’s high) to the social bond it can generate for those who join a gym class or running group. This is also just the most recent study which suggests that any amount of exercise, no matter how you do it, is far better than none at all.

The findings, say the authors, show that “substantial mental health benefits can be achieved with levels of physical activity even below public health recommendations.”