In older women, exercise was found to cut kidney stone formation, find researchers.
The study noted that even walking for a couple hours a week could cut the risk of developing this painful and common problem by about one-third, the New York Daily News reported.
Dr. Mathew Sorensen of the University of Washington School of Medicine in Seattle, who led the study, said that just getting a minimum amount of exercise could help.
Kidney stone problem is a little more common in men. But incidence has risen 70 percent over the last 15 years, most rapidly among women.
Obesity raises the risk, as do calcium supplements, which many women take after menopause. A government task force has recently advised against supplements for healthy older women, saying that relatively low-dose calcium pills don't do much to keep bones strong but make kidney stones more likely.
The new research involved nearly 85,000 women 50 and older in the government-funded Women's Health Initiative study.
Participants said how much exercise they usually got and that was translated into "METs" - a measure of how much effort an activity takes.
After about eight years, 3 percent of the women had developed a kidney stone. Compared to women who got no leisure-time exercise, those who got up to 5 METs per week had a 16 percent lower risk for stones.
The risk was 22 percent lower with 5 to 10 METs per week and 31 percent lower for 10 METs or more. Exercise beyond 10 METs added no additional benefit for kidney stone prevention. Exercise intensity didn't matter - just how much women got each week.
The researchers explained that exercise changes the way the body handles nutrients and fluids that affect stone formation.
Exercisers also sweat out salt and tend to retain calcium in their bones, rather than having these go into the kidneys and urine where stones form, they said.
They also tend to drink water and fluids afterwards, another plus for preventing stones.
Exercise is also known to cut the risk of heart disease, diabetes, high blood pressure and other conditions that raise the risk of kidney stones.
Next, researchers aim to study men and younger women to see if exercise helps prevent kidney stones in them, too.