Engaging in exercises such as cycling, aerobics and gymming for more than three hours a day can worsen mental health than not exercising at all, a study has found.

The study, published in journal The Lancet Psychiatry, found that people who exercised between three and five times a week had better mental health than people who exercised less or more each week.

Conversely, people doing extreme amounts of exercise might have obsessive characteristics which could place them at greater risk of poor mental health, the researchers said.

“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,” said Adam Chekroud, Assistant Professor at Yale University in the US.

“Doing exercise more than 23 times a month, or exercising for longer than 90 minute sessions is associated with worse mental health,” he added.

Exercise reduces the risk of cardiovascular disease, stroke, diabetes, and mortality from all causes, but its association with mental health remains unclear.

For the study, the team used data from 1.2 million adults across all 50 US states and included all types of physical activity, ranging from childcare, housework, lawn-mowing and fishing to cycling, going to the gym, running and skiing.

Team sports, cycling, aerobics and going to the gym were associated with the biggest reductions — 22.3 per cent, 21.6 per cent, and 20.1 per cent, respectively.

For people who had previously been diagnosed with depression, exercise was associated with 3.75 fewer days of poor mental health.

Even completing household chores was associated with reduction in poor mental health days of around 10 per cent, or around half a day less each month, the researchers said.

“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,” Chekroud said.