Married men do less of it than live-in boyfriends but they do twice as much as they did 20 years ago and now it's linked to mental health. What is this magical creation?

Housework.

Not just housework, but really any 20 minutes of physical activity, including the housework we all have to do anyway, is enough to boost mental health, reveals a large study published in the British Journal of Sports Medicine.

While regular exercise is known to be good for mental health, no one seems able to agree on how much, or what type of activity, is best. But housework might be that common denominator.

The findings are based on a representative sample of almost 20 000 men and women who were quizzed for the Scottish Health Survey about their state of mind and how much weekly physical activity they engaged in.

Over 3000 participants were deemed to be suffering from stress or anxiety, using a validated scoring system. But any form of daily physical activity was associated with a lower risk of distress, when other influential factors, such as age, gender, and the presence of a long term condition, were taken into account.

The range of activities, which proved beneficial, included housework, gardening, walking, and sports, although the strongest effect was seen for sports, which lowered the risk of distress by 33%.

The results also indicated that while just 20 minutes improved mental state, the more activity a person indulged in, the lower were their chances of psychological distress.

Physical activity curbs the risks of a range of serious diseases, such as heart disease and certain cancers, and it improves several biological risk factors, such as glucose intolerance and inflammation, which have themselves been linked to depression and dementia, say the authors.