The study, published ahead of print in the British Journal of Sports Medicine, found just 20 minutes of physical activity -- such as housework -- improved the mental state of people considered stressed but the more activity time people indulged in, the lower were their chances of psychological distress.

The findings are based on a representative sample of almost 20,000 men and women quizzed on mental state for the Scottish Health Survey, of which 3,000 were deemed to be suffering from stress or anxiety, using a validated scoring system.

The researchers at the University College London said any form of daily physical activity was associated with a lower risk of distress. Gardening and walking were as beneficial as housework, but the strongest effect was seen for sports which lowered the risk of distress by 33 percent.

Daily physical activity was associated with a lower risk of distress when other influential factors -- such as age, gender, and the presence of a chronic condition -- were taken into account.