A large study looked at whether exercise was tied to mental health in adults across the United States. The people studied were US adults aged 18 or older who answered a CDC phone survey in 2011, 2013 and 2015 (1,237,194 in all). The main comparison matched exercisers with similar people who did not exercise (852,068 people, of whom 627,510 exercised). Everyone was asked how many days in the past month their mental health was poor.
People who exercised reported fewer poor mental health days than matched people who did not (1·49 fewer days, or 43·2% fewer). Every type of exercise was linked to fewer poor days, with reductions ranging from 11·8% to 22·3%. The strongest links were for popular team sports (22·3% lower), cycling (21·6% lower), and aerobic or gym workouts (20·1% lower). The pattern was strongest at about 45 minutes per session and three to five times a week, and more exercise was not always better. Among people who had been diagnosed with depression before, exercisers reported a larger gap (3·75 fewer days, or 34·5%).
The study was taken at one point in time, so it cannot show that exercise caused the difference, and the link may run both ways. Mental health came from a single survey question, not a full assessment.
Source: Chekroud S, Gueorguieva R, Zheutlin A, et al.. Association between physical exercise and mental health in 1·2 million individuals in the USA between 2011 and 2015: a cross-sectional study. The Lancet Psychiatry (2018). doi:10.1016/S2215-0366(18)30227-X