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And it did not take a vigorous workout; regularexercise at any intensity level was linked to a lower breast cancer risk, theresearchers say.

The findings, reported in the journal Cancer,add to a number of past studies tying regular exercise to lower breast cancerodds.

One possible way is indirectly, by reducing bodyfat, lead researcher Lauren McCullough, of the University of North Carolina, said in an interview. Excess body fatis related to higher levels of certain hormones, including estrogen, as well assubstances known as growth factors, which can feed tumor development.

But exercise might also have direct effects,McCullough said -- by boosting the immune system or the body's ability to clearcell-damaging "free radicals."

"What we can say is, exercise is good foryou," she said "We don't know what it's going to do for any onewoman."

The study included 1,500 Long Island women with breast cancer and 1,550 cancer-free women thesame age. All were interviewed about their lifetime exercise habits and otherlifestyle factors, like smoking and drinking.

Those who'd exercised for 10 to 19 hours a weekin their "reproductive years" -- the years between having their firstchild and going through menopause -- were one-third less likely to have breastcancer than women who'd been sedentary during that time.

Women who'd started exercising after menopausealso had a lower risk. If they averaged 9 to 17 hours a week, they were 30percent less likely to have breast cancer than their inactive peers.

Of course, women who exercise can be differentfrom sedentary women in many ways. So McCullough's team accounted fordifferences in education, income, smoking and certain other factors. Exercisewas still linked to lower breast cancer risk.

Then the researchers took a closer look at bodyweight.

They found among relatively lighter women,exercise was linked to lower breast cancer. And for obese women, it may havemitigated the increased breast cancer risk tied to their excess pounds.

For now, McCullough said her findings supportwhat's already recommended for good health. And they suggest that women mightbenefit even if they start exercising after menopause.

"It's never too late to start," shesaid "Our evidence suggests that if you start after menopause, you canstill help yourself."

There was no link seen between exercise andbreast cancer for the nearly 1,000 women in the study who developed breastcancer before menopause.

According to McCullough, that may be becausebreast cancer earlier in life has different causes compared with aftermenopause -- when most breast cancers occur.