NEW YORK (Reuters Health) - Active women are less likely to develop urinary incontinence as they age, a new study shows.

Fewer than one in three women 65 and older exercise for at least half an hour at least five days a week, and fear of incontinence has been suggested as one reason to explain why older women are not more active, according to Dr. Kim Danforth of Harvard Medical School and colleagues.

But it's likely that exercising could actually reduce incontinence risk by strengthening the pelvic floor muscles, Danforth and her team point out.

To investigate, they looked at data from the Nurse's Health Study, which includes more than 100,000 women followed since 1976. In 2000, the women ranged in age from 54 to 79 years, and 2,355 reported developing urinary incontinence between 2000 and 2002.

The more active the women were, the less likely they were to develop incontinence, according to the study reported in the journal Obstetrics and Gynecology this month.

The most active women were 15 to 20 percent less likely to report leaking urine than the least active women. Women who reported the most walking -- the most common type of physical activity among the women -- had a 26 percent lower risk of urinary incontinence than those who walked the least.

The association between exercise and lower incontinence risk was strongest for stress urinary incontinence, in which a person leaks urine due to stresses such as sneezing, coughing or lifting a heavy object. The most active women were 30 percent less likely to report stress incontinence than the least active women.

The link was seen among women at all categories of body weight; even slim women who were inactive were at greater risk of incontinence than active, lean women. This supports the idea that exercise helped prevent incontinence not by promoting weight loss, but by strengthening the pelvic floor muscles, the researchers note.

"Our results suggest that women who avoid exercise due to concern about becoming incontinent might be reassured that low-impact activity does not appear to increase the risk of developing incontinence," Danforth and colleagues conclude.