Two Studies Shed Light on the Link Between Fitness and Breast Cancer
by Helen Zhang, age 15
Studies conducted by the American Cancer
Society and the University of Minnesota indicate that exercise may be
a vital key to reduce the risk of breast cancer. Two reports
published in the journal Cancer
Epidemiology, Biomarkers & Prevention
detail the positive influence of exercise and explain the study’s
The latest and largest study conducted at
American Cancer Society followed 73,600 postmenopausal women, aged 50
to 73, for almost two decades. Researchers collected survey data on
the lifestyles and activities of these women. About half the group
reported walking as their only form of exercise. Over the course of
the study, 4,760 of the women developed breast cancer.
The researchers ultimately discovered that
women who walk at least seven hours per week have a 14 percent lower
risk of developing breast cancer than those who walk fewer than three
hours per week. Furthermore, the most active women—those who
exercised up to ten hours per week—reduce their risk of developing
breast cancer by 25 percent in comparison to the least active women.
The second study done by public health research
at the University of Minnesota looked at younger, non-active women
and their estrogen levels. The study was split into two groups—those
in the first group remained sedentary while those in the second group
attended an aerobic exercise program five times a week for four
months. Researchers tested levels of estrogen and estrogen
metabolites, substances that form when estrogen is broken down,
through urine samples of the participants.
By looking at the ratios of different estrogen
metabolites, researchers can determine breast cancer risk. The
results showed the sedentary group had no change in their estrogen
metabolites; however, the active group’s ratio of metabolites
indicated a lower risk of cancer. In addition, the active women lost
body fat and gained muscle.
The ability of exercise to change the ratio of
estrogen metabolites and to lower body fat levels may reduce risks of
breast cancer. However, this study does not prove that exercise can
eliminate all chances of cancer. Exceptions exist; even those who are
very active can develop cancer.
“There is still a very great deal that we
don’t know,” says Dr. Alpa V. Patel, a senior epidemiologist at
the American Cancer Society and senior author of the first study.
She adds that walking is an easy, inexpensive type of exercise for
everyone. “But physical activity, and especially walking, are so
simple and so accessible to most women. So why not?”
New York Times]