Exercise Lowers Breast Cancer Risk
Moderate Activity Level Cuts Risk of Aggressive Cancer Type by a Third in Older Women
Dec. 11, 2006 -- Regular exercise helps protect older women against breast
cancer -- in particular, a less common but hard-to-treat form of the
disease, a new study shows.
In a study that looked at the link between exercise and breast cancer in more than
36,000 women, researchers found a 34% reduction in the likelihood of getting
one specific type of breast cancer in women with high levels of physical
The researchers from the Mayo Clinic in Rochester, Minn., conclude that
postmenopausal women can lower their risk of developing breast cancer by
engaging in moderate exercise.
The strongest evidence of a benefit was in preventing an aggressive,
hormone-driven cancer known by doctors as estrogen-receptor positive and
progesterone-receptor negative (ER+/PR-).
Women with a high level of physical activity were a third less likely to
develop that type of cancer than women in a low activity group.
That high level of exercise also resulted in a 14% reduction in breast
cancer risk overall, compared with women with low physical activity. However,
after adjusting for body mass index (BMI) in
the women, the risk reduction dropped to 9% -- a number not considered
significant in this study.
BMI is used to help determine obesity status. Obesity has
been identified as a strong independent risk factor for breast cancer.
The findings are reported in the latest issue of Archives of Internal
"This study provides additional evidence that physical activity helps
protect against breast cancer," researcher James R. Cerhan, MD, PhD, tells
WebMD. "And it appears that it is never too late to begin an exercise
program, even if you haven't been physically active in the past."
The Importance of Tumor Type
The new study is not the first to find exercise beneficial for lowering
risk. But it is the first large investigation to quantify this benefit by tumor
Cerhan and colleagues used data from a large, ongoing health trial of
postmenopausal women, known as the Iowa Women's Health Study, in their effort
to understand the impact of exercise on different types of breast cancer.
All participants were between the ages of 55 and 69 in 1986, when they
filled out a 16-page health questionnaire. The women were asked how often and
with what intensity they engaged in physical activity.
High physical activity (9,111 women) was defined as vigorous activity --
such as jogging, swimming, or racket sports -- two or more times each week, or
moderate activity -- such as bowling, golf, or walking -- more than four times
Medium physical activity (10,030 women) was defined as engaging in a
vigorous activity once a week or in moderate activity one to four times a
About 17,222 women got less exercise than this and were recorded in the low
physical activity group.
Of the women in the study with breast cancer of a known type, roughly 14%
had the progesterone negative, or ER+/PR-, tumors.
This type of tumor is more aggressive than a progesterone-receptor positive
High physical activity was associated with a 34% reduction in the risk of
the progesterone-negative tumors, and this risk reduction did not appear to be
influenced by body weight, Cerhan says.