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Preventing
Breast Cancer
One
way to significantly reduce breast-cancer risk is as close as
the sneakers in your closet. Nearly 30 studies have shown
that women who exercise at moderate to vigorous levels for
three or more hours per week reduce their risk of getting
breast cancer by 30 percent to 40 percent. That's
about as much reduction in risk as provided by the drug
tamoxifen, but without the side effects.
The
American Cancer Society and the World Health Organization's
International Agency for Research on Cancer recently developed
guidelines for cancer prevention focusing on physical
activity, weight control and nutrition.
They both conclude that the evidence linking exercise to a reduced risk
for breast cancer is convincing, and both recommend that women
engage in moderate to vigorous exercise for at least 30
minutes per day, preferably more for optimal benefit.
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Hormones
Scientists
believe that hormones are the link between exercise and
breast-cancer protection. Exercise reduces levels of
estrogen, testosterone, insulin, and growth factors, all
of which may either cause breast cancer or prompt it to
grow faster and larger. Women with high levels of these
hormones in their blood have a high risk of developing
breast cancer.
Research
recently presented at the American Association for Cancer
Research annual meeting in San Francisco may shed some
additional light. Dr. Celia Byrne and colleagues (from
Harvard University) studied the relationship between
C-peptide, a marker of insulin production, and risk for
breast cancer in the Nurses' Health Study, which involves
more than 32,000 women. They measured C-peptide in blood
from the 463 women who developed breast cancer and
compared it with blood C-peptide levels in a sample of
women who did not develop the disease.
They
found that those who had the highest C-peptide levels had
a statistically significant, 70 percent greater chance of
developing breast cancer compared with women who had the
lowest levels. In the same study, they found that
C-peptide levels were higher in overweight and obese women
and were lower in women who were physically active. Other
studies have shown that insulin levels drop right after an
exercise session, so the beneficial effect is
immediate.
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Just
30 Minutes a Day
To
reduce the risk of breast cancer, women should engage in
aerobic exercise for at least 30 minutes every day, preferably
more. Walking is an excellent aerobic activity and can be done
easily by most women.
Small
things count — walking down the hall to talk with a
colleague rather than e-mailing, walking or biking to work,
taking physically active vacations with family, using stairs
rather than elevators. Those who are already active can get
more benefit by doing more exercise — as long as they don't
overdo it. A good rule of thumb is to increase the time spent
exercising no more than 10 percent per week.
Those
who embark on an intense training program (such as preparing
for a marathon) should make sure they get enough rest
including one day of rest from training every week. Many
of the benefits of exercise in breast-cancer prevention may
also apply for women who have had breast cancer. Overweight and obese breast-cancer patients have poorer survival than
lighter-weight women. Exercise can therefore be an important
part of the breast-cancer recovery process.
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