© Provided by Shutterstock Men doing push-ups Exercising for 90 minutes a day or more could make mental health worse, a major new research suggests.

In the largest study of its kind researchers at Yale University and Oxford looked at the fitness regimes of 1.2 million people and compared them with how often they felt depressed or stressed.

People who did no extra physical activity said they felt low an average of 3.4 days of the month, while those who exercised regularly reported just two days, a reduction of 43 per cent.

However the researchers discovered that more exercise was not always better, with 45 minutes three to five times a week found to have the biggest benefits.

People who exercised for periods of 90 minutes at a time suffered up to one day extra of poor mental health each month compared to those who stuck to 45 minute sessions.

“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 Dr Adam Chekroud, Assistant Professor of Psychiatry at Yale University.

© Provided by Shutterstock Women exercising in fitness studio “Doing exercise more than 23 times a month, or exercising for longer than 90 minute sessions is associated with worse mental health.

“It’s difficult to speculate what is driving the effect. It is easy to imagine why someone might have poor mental health if they are exercising more 6 or 7 days per week. They could be getting run down (physically exhausted) or burned out (mentally), both of which might make them feel stressed or depleted.”

Exercise is known to reduce the risk of cardiovascular disease, stroke, diabetes, and early death from all causes, but its association with mental health is not so clear.

The study included all types of physical activity, ranging from childcare, housework, lawn-mowing and fishing to cycling, going to the gym, running and skiing.

© Provided by Shutterstock All types of exercise were associated with improved mental health, but the strongest benefits were seen for team sports, cycling, aerobic and gym exercise which saw a reduction in poor mental health days of 22.3 per cent, 21.6 per cent, and 20.1 per cent, respectively.

Even completing household chores was associated with an improvement of around 10 per cent, or around half a day less depression or stress each month.

Commenting on the study, which was published in The Lancet Psychiatry, Prof Stephen Lawrie, Head of Psychiatry at the University of Edinburgh, said: “I would summarise the results as indicating that activity, is good for mental health – but that one can do too much. Every second day for 45-60 mins might be optimal.

Watch: Mental Health: Top facts from mental health charity Mind (provided by International Business Times)

“Certainly, the results suggest that exercising every day is associated with worse mental health. I suspect we all know people who seem ‘addicted’ to exercise and if this starts to impact on other aspects of life – like foregoing social activities because one has to be up at the crack of dawn to run several miles – it might actually be bad for people.”

Dr Brendon Stubbs, NIHR Clinical Lecturer, King's College London’s Institute of Psychiatry, added:” The message reinforces government guidelines which recommend people should seek to achieve over 150 minutes of physical activity per week, which could include 30 minutes 5 times a week.

“The good news is that lots of different types of physical activity appear to be associated with better mental health. Thus, the key message from this paper and the wider literature is that people should find a physical activity they enjoy and try and do it regularly but just getting started is key.”

Related: 12 workout habits you think are good for you, but aren't (provided by INSIDER)