Strenuous physical activity associated with lower
breast cancer risk
Newswise — Women who regularly
engage in strenuous physical activity may have a
lower risk of developing both invasive breast cancer
and in situ (early-stage) breast cancer than women
who do not, according to a report in the February 26
issue of Archives of Internal Medicine, one
of the JAMA/Archives journals.
“Few established risk factors
for breast cancer are easily modifiable,” the
authors write as background information in the
article. Physical activity has been associated with
breast cancer risk and may be one of the few risk
factors that women can control.
“Questions remain regarding the
amount and intensity of physical activity and the
periods when activity provides the greatest breast
cancer risk reduction.”
Cher M. Dallal, M.S.,
University of Southern California, Los Angeles, and
colleagues studied 110,599 women age 20 to 79 who
were part of the California Teachers Study,
established in 1995 and 1996.
At the beginning of the study,
the women were asked about their average
participation in moderate (such as brisk walking,
golf or volleyball) and strenuous (including
swimming laps, aerobics and running) physical
activity from high school to their current age and
also in the past three years. The women also
provided information about other breast cancer risk
factors, including race, family history and use of
hormone therapy.
Through 2002, 2,649 women were
diagnosed with invasive breast cancer and 593 with
in situ breast cancer. Women who reported
participating in strenuous activity for more than
five hours per week over the long term had a 20
percent lower risk of invasive breast cancer and 31
percent lower risk of in situ breast cancer than
women who participated in less than 30 minutes of
strenuous activity per week. “Long-term moderate
physical activity and strenuous and moderate
activity in the past three years were not associated
with invasive breast cancer,” the authors write.
Similarly, moderate activity did not appear to
influence the risk of in situ breast cancer.
The researchers also examined
the association between strenuous physical activity
and the risk of breast cancer by hormone receptor
type, or which hormones can bind to proteins on the
surface of the tumor. Strenuous activity appeared to
be associated with a lower risk of
estrogen-receptor–negative but not
estrogen-receptor–positive breast cancers.
“In summary, these results
provide additional evidence supporting a protective
role for long-term strenuous recreational physical
activity on risk of invasive and in situ breast
cancer, whereas the beneficial effects of moderate
activity are less clear. For invasive breast cancer,
strenuous and moderate physical activity affect risk
of estrogen-receptor–negative tumors, but neither
affects risk of estrogen-receptor–positive tumors.”