By Robert Preidt
An analysis of data from 1.2 million people in the United States found they reported 3.4 days a month of poor mental health on average. But those who were physically active had 1.5 fewer "down" days a month than those who were not active.
Being active for 45 minutes three to five times a week was associated with the biggest benefit.
Exercise had the greatest impact on people with diagnosed depression, the findings suggested. In this group, those who exercised had 3.75 fewer days of poor mental health a month than those who were inactive -- 7.1 days versus 10.9 days.
"Depression is the leading cause of disability worldwide, and there is an urgent need to find ways to improve mental health through population health campaigns," said study author Adam Chekroud. He's an assistant professor of psychiatry at Yale University.
The study included 75 types of physical activity -- from sports and exercise, to childcare, housework and lawn mowing.
Team sports, cycling, aerobics and going to the gym were associated with the largest reductions in poor mental health days, possibly because they reduce social withdrawal and isolation, the study authors noted.
People who were active three to five times a week had better mental health than those who exercised more or less, according to the study published Aug. 8 in The Lancet Psychiatry.
Thirty to 60 minutes of physical activity was associated with the biggest reduction in down days (about 2.1 fewer days each month). But exercising more than three hours a day appeared to be worse for mental health than not exercising at all, the researchers said.
The associations seen in the study don't prove a cause-and-effect relationship, however.
"Previously, people have believed that the more exercise you do, the better your mental health, but our study suggests that this is not the case," Chekroud said in a journal news release. Exercising more than 23 times a month or for more than 90 minutes at a pop was linked to poorer mental health, the researchers said.
The links appeared to be universal.
"Exercise is associated with a lower mental health burden across people no matter their age, race, gender, household income and education level," Chekroud said. "Excitingly, the specifics of the regimen -- like the type, duration and frequency -- played an important role in this association."
Researchers hope to use the information to personalize exercise recommendations.