It doesn’t matter where you live, what your gender is, or how old you are—regularly sliding into a pair of running shoes means your risk for developing depression is lower than if you never exercise.
An international team of researchers from Kings College in London came to that conclusion after taking stock of years of evidence from all over the world. To begin their work, the scientists searched for any past studies having to do with physical activity and depression, which yielded a mountain of results, more than 13,000 papers. After a painstaking, multi-step review process, they boiled the number of applicable studies down to 49, which covered nearly 267,000 people across Asia, Europe, North America, and Oceania. Then the researchers began their meta-analysis, a statistical approach to research that involves consider a number of studies, then combining the results to paint a clearer picture of what all the data tell us.
“To our knowledge, this is the first study to meta-analyze the relationship between physical activity levels and incident depression,” the researchers wrote in the resulting paper, released today (April 24). “Study findings indicate that across 49 studies, higher physical activity levels are associated with a decreased odds of developing future depression.”
Their work was published in the American Journal of Psychiatry, and it bolsters mounting evidence (paywall) that exercise and moving around correlates with lower depression risk for those who’ve never had mental health issues before. Still, just what’s happening on a biochemical level remains a mystery to scientists, who have more work to do to better understand what it is about physical activity that can help prevent depression. The researchers involved in the latest study hypothesize that being active increases neurogenesis—nervous tissue growth—and in doing so activates our endocannabinoid system, which has in the past been linked to exercise-induced euphoria, also known as a runner’s high.
The finding is important because it could help reshape health policy, putting a greater emphasis on exercise to allay depression at the population level—about one in 10 adults in the US has grappled with depression at some point in their life. Getting more people to exercise would have lots of other positive health effects as well. There’s evidence that exercise can help protect against heart disease, diabetes, and high blood pressure.
Past studies have noted that the impact of physical activity in keeping depression at bay may vary depending on a person’s gender; however the assumption was not supported by the meta-analysis, which noted the effects of physical activity were similar for both genders. The researchers were also able to deduce that staying active had protective effects on depression across people of all ages.
The paper doesn’t bother with suggesting more research is needed to determine whether there’s a connection between physical activity and depression risk. That’s pretty clear, the study authors argue. Instead, they write, the next steps are “to evaluate the minimum physical activity levels required as well as the effects of different physical activity types and ‘dosages’ on subsequent risk for depression.”