Both anecdotal and scientific evidence has suggested that physical activity can be a great ally in fending off or fighting the symptoms of depression, which affects around 40 million adults in the United States each year, according to the Anxiety and Depression Association of America. After assessing numerous specialist studies, a new review concludes that exercise can help to both prevent depression and treat its symptoms. However, current treatments for depression often fail to include this lifestyle adjustment, despite the strong evidence. In their review, the authors started by analyzing the data from 49 prospective studies with a total of 266,939 participants between them. The analysis revealed that studies that had adjusted for potential confounding factors — such as age, biological sex, or smoking status — indicated that exercise could help reduce depression risk by 17%. So far, specialists have suggested that physical activity's positive effect on mental health may be because exercise can help reduce inflammation, protect cellular health, and help brain cells regenerate. "Physical activity can confer protection from the development of depression in children, adults, and older adults. These effects are evident in all continents. Also, among people with depression, exercise can be used for acutely managing symptoms. A robust body of evidence from randomized controlled trials demonstrates that exercise is effective in treating depression.", conclude the authors.