Exercise reduces breast cancer risk in black women

By Anthony J. Brown, MD

NEW YORK (Reuters Health) – With a few hours of exercise
each week, black women can reduce their risk of breast cancer
to the same extent that white women can, new research suggests.

“The results indicate that the more exercise you do over
your lifetime, the greater your reduction in breast cancer risk
will be,” lead author Dr. Leslie Bernstein, from the University
of Southern California in Los Angeles, told Reuters Health. “In
general, I think you need to do 3 to 4 hours of exercise per
week to see a strong protective effect.”

Until now, “there really had not been a study of the breast
cancer-preventing effects of exercise in African American
women,” Bernstein said. “The results indicate that they glean
as much benefit from physical activity as white women do.”

The findings, which appear in the Journal of the National
Cancer Institute, are based on a comparison of lifetime
recreational exercise between 4,538 patients with breast cancer
and 4,649 women without breast cancer. Roughly, a third of
subjects in each group were black and the remainder was white.

As lifetime exercise activity rose, the risk of breast
cancer fell, the report indicates, with no statistically
significant difference noted between black and white women.
Compared with inactivity, annual lifetime exercise activity
that exceeded the average level for active comparison subjects
reduced their risk of developing breast cancer by 20 percent.

However, physical activity did not help prevent breast
cancer in women who had a close relative with the malignancy.
On the other hand, the beneficial effect of exercise on breast
cancer risk was not affected by disease stage, tumor type or
other related factors.

As to how exercise reduces the risk or breast cancer,
Bernstein said that the major hypothesis is that it involves
changes in the hormones estrogen and progesterone. “However,
there are other possible mechanisms that are being explored,”
including changes in insulin and fats.

Bernstein said her group is currently involved in a similar
study looking at the impact of physical activity on the risk of
other cancers in women.

SOURCE: Journal of the National Cancer Institute, November
16, 2005.