June 26 Women who exercise moderately may be
less likely than their inactive peers to develop breast cancer
after menopause, according to a U.S. study.
Researchers, whose study was published in the journal
Cancer, found that of more than 3,000 women with and without
breast cancer, those who'd exercised during their childbearing
years were less likely to develop the cancer after menopause.
The same was true when women took up exercise after
menopause, said the group, led by Lauren McCullough at the
University of North Carolina, Chapel Hill.
"What we can say is, exercise is good for you," McCullough
"It's never too late to start. Our evidence suggests that if
you start after menopause, you can still help yourself."
The findings add to a number of past studies tying regular
exercise to lower breast cancer rates. But all the studies only
point to a correlation and don't prove that exercise itself is
what reduces women's breast cancer risk.
There are reasons, though, to believe it can, said
One possible way is indirectly, by cutting body fat, she
said. Excess body fat is related to higher levels of certain
hormones, including estrogen, as well as substances known as
growth factors which can feed tumor development.
But exercise might also have direct effects by boosting the
immune system or the body's ability to clear cell-damaging "free
In the study, which included 1,500 women with breast cancer
and 1,550 cancer-free women of the same age, all were
interviewed about their lifetime exercise habits and other
lifestyle factors, like smoking and drinking.
The researchers found a connection between exercise and
breast cancer risk only among women who had already gone through
Those who'd exercised for 10 to 19 hours a week in their
"reproductive years" - the years between having their first
child and going through menopause - were one-third less likely
to have breast cancer than women who'd been sedentary during
Women who'd started exercising after menopause also had a
lower risk. If they averaged 9 to 17 hours a week, they were 30
percent less likely to have breast cancer than their inactive
Of course, women who exercise can be different from
sedentary women in many ways. So the researchers accounted for
differences in education, income, smoking and certain other
factors. Exercise was still linked to lower breast cancer risk.
Then the researchers took a closer look at body weight.
They found that among relatively lighter women, exercise was
linked to lower breast cancer risks. And for obese women, it may
have mitigated the increased breast cancer risk tied to their
There was no link seen between exercise and breast cancer
for the nearly 1,000 women in the study who developed breast
cancer before menopause. That may be because beast cancer
earlier in life has different causes.
The study had a number of limitations, including relying on
women's memories of their exercise habits over a lifetime. In
addition, any study like this can only look at broad patterns.
For now, McCullough said her findings support what's already
recommended for good health - to get exercise.
(Reporting from New York by Amy Norton at Reuters Health;
editing by Elaine Lies and Bob Tourtellotte)