Thanks to a recent study conducted by Dr Jo Barton for the University of Essex, said that as well as protecting against future health threats, outdoor exercise could even increase life expectancy.

Scientists are now calling for doctors to prescribe 'green exercise' - working out doors or the back garden - for patients who suffer from mental illness.

Barton's research is the first to determine exactly how much time people have to spend in green spaces to decrease the risk of illness and improve the general sense of well-being.

"The study showed there was a significant increase in people's self-esteem and mood, particularly when they exercised in the wilderness or by water" Dr Barton said.

"This is because historically we are drawn to water to survive and it is in our genetic make up to be at one with nature." Dr Barton and her research colleague Jules Pretty, whose findings are published in the Journal of the American Chemical Society, studied more 1,200 people's reactions to 'green' exercise in locations across Britain.

Read more: Daily Mail News Article 5th May 2010