April 9 (HealthDay News) -- Scrubbing the tub and other forms of housework may clean your house and boost your mood.

In fact, as little as 20 minutes of any kind of physical activity a week helped mental health, although the more vigorous the activity, the greater the benefit, said the authors of a study published online Thursday in the British Journal of Sports Medicine.

"There's such a pervasive feeling in this country that, if there's a problem, there's always a pill to fix it," said Dr. Suzanne Steinbaum, director of Women and Heart Disease at Lenox Hill Hospital in New York City. "This study is just reminding us that it doesn't take much to actually have an effect even on your mood."

The physical benefits of exercise are well known: It reduces the risk of heart disease, type 2 diabetes, high blood pressure and even some cancers, among other things.

The mental benefits are less clear, although exercise is thought to improve blood flow and reduce inflammation, which have been related to depression and dementia. Exercise might also improve mood by reducing stress levels.

"It's pretty clear that physical activity does have some kind of positive relationship to good mental health," said Dr. Jane Ripperger-Suhler, assistant professor of psychiatry and behavioral science at Texas A&M Health Science Center College of Medicine and a psychiatrist with Scott & White Mental Health Center in Temple. "They [the study authors] are trying to figure out how much you need to do."

For the new study, almost 20,000 men and women participating in the 1995, 1998 and 2003 Scottish Health Surveys answered questionnaires about physical activity and "psychological distress."

Daily physical activity of any kind -- including housework, gardening, walking, and sports -- was associated with a 41 percent lower risk of psychological distress. But sports reduced the risk of mood lows the most -- by 33 percent.

And just in case women are thinking this study is a ploy to engage in more housework, think again. The study showed that more sports and overall activity increased your mood even more, but extra mopping and scrubbing didn't.

"The message is do a little bit of housework and a lot of sports," Ripperger-Suhler said.

According to the study authors, from University College London, this appears to be the first research to look at different specific activities in relation to mental health. The study wasn't designed to look at a cause-and-effect relationship, only that a relationship exists.

SOURCES: Suzanne Steinbaum, D.O., director, Women and Heart Disease, Lenox Hill Hospital, New York City; Jane Ripperger-Suhler, M.D., assistant professor of psychiatry and behavioral science, Texas A&M Health Science Center College of Medicine and psychiatrist, Scott & White Mental Health Center, Temple, Texas; April 10, 2008, British Journal of Sports Medicine, online