Moderate exercise improves mental health but overdoing it does more harm than good, researchers have found.
A huge study of 1.2million people found those who exercised were – on average – stressed and depressed on fewer days than those who did not.
But experts also discovered a threshold beyond which the benefits began to be reversed.
Those who did the most exercise – more than five times a week or more than three hours a day – actually had worse mental health than those who did nothing at all.
The scientists, led by experts at Yale University in the US and Oxford University, found that exercising for 45 minutes three to five times a week was associated with the biggest benefits. Doing more than this saw the benefits decline.
The researchers, whose findings are published in the Lancet Psychiatry journal, believe excessive exercise might be linked to obsessive behaviour.
But they stressed that more moderate exercise was definitely beneficial. Even doing chores around the house or pottering in the garden cut the time spent depressed by 10 per cent, they found.
Dr Adam Chekroud, assistant professor of psychiatry at Yale, said: ‘Depression is the leading cause of disability worldwide, and there is an urgent need to find ways to improve mental health through health campaigns.
‘Exercise is associated with a lower mental health burden across people no matter their age, race, gender, household income and education level.
‘Excitingly, the specifics of the regime, like the type, duration, and frequency, played an important role in this association. We are now using this to try to … match people with a specific exercise regime that helps improve their mental health.’