More
Evidence That Exercise Reduces Cancer Risk
from the
American Cancer Society
Vigorous Activity Lowers Rate of Ovarian,
Colorectal and Breast Cancer
Three recently published studies find that
people who exercise lower their cancer risk. But all three point out that the
exercise can’t be a walk in the park. It needs to be vigorous.
A study of women in China found that those
with a high level of vigorous activity had a lowered rate of ovarian cancer.
Reporting in the International Journal of Cancer (Vol. 105, No. 6:
838-843) Min Zhang and colleagues compared the physical activity of women with
ovarian cancer to that of women without this disease. They looked at how much
effort the women expended at work or exercise and how much they sweated with
these activities.
Women with a high level of physical activity
cut their ovarian cancer risk in half. This meant they engaged in one of the
following activities:
- "vigorous work" like moving heavy
furniture or digging for at least 20 hours a week;
- moderate activity such as brisk walking
or bicycling for 30 hours a week;
- strenuous sports at least two hours a
week;
- working or exercising hard enough to
sweat at least three times a week.
All this seems like a lot of activity and it
may not carry over directly into guidance for women in the US. Chinese women
may normally have a high level of physical activity so they need to work even
harder to lower their risk of ovarian cancer. Also, China's ovarian cancer
rates overall are lower than US rates -- another factor that would complicate a
direct comparison.
Women Cut Breast Cancer Risk
with Exercise
But even U.S. women need to exercise
vigorously to lower their risk of another cancer, breast cancer. A study led by
Alpa Patel, of the American Cancer Society, found that women who were very
active lowered their risk of breast cancer by nearly 30%.
In their report, published in the journal
Cancer Causes and Control (Vol. 14, No. 6: 519-529), Patel and
colleagues examined the relationship of exercise to breast cancer in
postmenopausal women. Although any physical activity appeared to have some
benefit, the 30% reduction in breast cancer rate occurred in women whose
exercise was the equivalent of swimming, running or jogging at least six hours
a week.
Women could achieve the same effect by
walking or dancing; they would just need to do it for twice as long.
Colorectal Cancer Rate Drops
with Physical Activity
In a third study, this time of colorectal
cancer, researchers from the University of Utah and Kaiser Permanente in
Oakland, California, found that both men and women lowered their risk of this
disease with physical activity. In the report, published in the American
Journal of Epidemiology (Vol. 158, No. 3: 214-224) the researchers, led by
Dr. M. L. Slattery, pointed out that vigorous activity provided the greatest
benefit.
Men and women who exercised the equivalent
of jogging five or more hours a week lowered their risk of colorectal cancer by
40% to 50%. Some benefit came from less vigorous activity, particularly for
rectal cancer.
Scientists Not Certain How
Exercise Works
The researchers from these three studies all
point out that studying the effect of exercise on cancer risk is an uncertain
science. There may be other characteristics about people that lead them to
exercise and also reduce their risk of cancer. One example might be that their
concern for their health has led them to eat more fruits and vegetables, which
can also reduce cancer risk. Another is that cancer rates are often higher in
obese people and the more active people are generally thinner.
But the researchers didn’t think that
weight alone accounted for the differences. There seems to be some biologic
connection between exercise and lowering the risk of some cancers. Although
there are many explanations, none have been proven and scientists are still
looking for that link. People who want to lower their risk for these three
cancers benefit from knowing that vigorous exercise works.
The
American Cancer Society
recommends that adults engage in at least moderate activity for 30 minutes or
more on five or more days of the week; 45 minutes or more of moderate to
vigorous activity on five or more days per week may further enhance reductions
in the risk of breast and colon cancer. |
