Exercise & Breast Cancer ~ [Issue 0500-1]
May 02, 2000 12:11 PDT
EXERCISE AND BREAST CANCER
According to National Cancer Institute (NCI) estimates, approximately
one woman in eight will develop breast cancer at some point in her
life. Worldwide, breast cancer is the most common cancer among women
- twenty-one percent of total cancers.
Now, however, new studies offer hope of reducing that number and
improving the odds.
Building on previous studies, including a study in Norway which
showed women who got four hours per week of exercise decreased breast
cancer risk by about thirty-three percent, research compiled at
Brigham and Women's Hospital in Boston confirms the value of physical
activity in lowering the likelihood of developing the disease.
Writing in the Archives of Internal Medicine, Beverly Rockhill, PhD
and colleagues note that "Increased physical activity has been
hypothesized to prevent breast cancer, largely by reducing cumulative
lifetime exposure to circulating ovarian hormones."
Analyzing 16 years of data from the Nurses' Health Study, Rockhill
and her team found the incidence of breast cancer (3,137 cases among
121,701 participants) to be twenty percent lower in those women who
exercised an average of once per day, compared to those whose
physical activity totaled one hour a week or less.
Previously, another study using data from the Nurses' Health Study
examined the effectiveness of vitamins A, C and E, as well as
carotenoids, in lowering breast cancer risk among pre- and
postmenopausal women. In that study, published in the September 21
issue of the Journal of the National Cancer Institute, Dr. Shumin
Zhang and colleagues reported in an inverse association between the
consumption of fruits and vegetables containing these vitamins and
the risk of premenopausal breast cancer.
Although the 16-year follow-up period of the Brigham and Women's
study represents the most comprehensive analysis to date of the
possible benefits of exercise in reducing breast cancer risk, author
Rockhill agrees even this may not be enough to accurately measure the
relationship. "Even our cumulative 16-year averaging does not
represent a 'lifetime' average," she notes, hinting that the actual
benefits of exercise might be even more dramatic. "It is possible,"
she writes, "that misclassification (with regard to lifetime average)
introduced by our 16-year follow-up measure may have attenuated an
even stronger inverse relationship."
For women who might not be inclined to engage in vigorous activities
such as aerobics, there is more good news. For most of the women
participating in the study, the exercise of choice was walking.
Furthermore, researchers found "no evidence in these data that
vigorous physical activity (at least as measured over a 10-year
follow-up period) is more likely to reduce breast cancer risk than
less strenuous activity."
Unfortunately, admit the authors, "there is currently no scientific
consensus on the critical time period of exposure or on the intensity
or frequency of physical activity needed to influence breast cancer
risk." Still, they note, "Most previously identified risk factors for
breast cancer are reproductive and menstrual events that cannot be
readily altered. The protective effect of exercise on breast cancer
risk in the women whom we studied suggests that physical activity
offers one modifiable lifestyle characteristic that may substantially
reduce a woman's lifetime risk of breast cancer."
In short, as Rockhill summed up her findings in speaking to the
Associated Press, "All the evidence suggests that there's nothing to
lose by women being physically active." What's more, considering the
evidence, there could well be a life to gain.