Exercise and Breast-Cancer Prevention:
Study Finds It's Never Too Late to
Start, and the Activity Need Not Be Strenuous
Moderate activity, even when started in a woman's postmenopausal
years, can cut her risk of breast cancer by about 20 percent.
SEATTLE,
Sept. 11, 2003 - Increased physical activity, even when begun later in
life, reduces overall breast-cancer risk by 20 percent among women at
all levels of risk for the disease, according to a study led by
researchers at Fred Hutchinson Cancer Research Center. Their findings
appear in the Sept. 10 issue of the Journal of the American Medical
Association.
What's
more, the activity need not be strenuous but it should be done
consistently, such as taking a brisk, 30-minute walk five days a week,
said lead investigator Anne McTiernan, M.D., Ph.D., a member of Fred
Hutchinson's Public Health Sciences Division and director of the
center's Prevention Center.
"We
thought it was important to determine if moderate-intensity physical
activities, such as walking, biking outdoors or easy swimming, when
initiated later in life, can reduce the risk of breast cancer, since
these types of activities are achievable for most women," said
McTiernan, who is also the lead author of "Breast Fitness: An Optimal
Exercise and Health Plan for Reducing Your Risk of Breast Cancer" (St.
Martin's/Griffin Trade Paperback).
"Our
results suggest that indeed, moderate activity, even when started in a
woman's postmenopausal years, can cut her risk of breast cancer by
about 20 percent, suggesting that physical inactivity may be a
modifiable breast-cancer risk factor in older women." In addition, the
researchers found that regular exercise also causes a similar
reduction in overall breast-cancer incidence among women considered to
be at highest risk for the disease, such as those with a strong family
history of breast cancer, those who've never had children and those
who take combination estrogen/progestin hormone-replacement therapy.
"The good
news is that even though HRT increases the risk of breast cancer,
exercise is something women can do to lower this risk if they choose
to continue taking HRT to manage the symptoms of menopause or to
prevent osteoporosis," McTiernan said.
McTiernan
and colleagues also found that the less a woman weighs, the more
regular, moderate exercise appears to have a protective effect. Women
of low to normal weight - and even those who were moderately
overweight - who exercised the equivalent of 10 hours of walking each
week experienced breast-cancer risk reductions of more than 30
percent. Breast-cancer risk didn't budge, however, among women
exercisers who were significantly overweight or obese.
The
weight status of the participants was determined by calculating their
body-mass index, or BMI, a measure of body fat based on height and
weight. The World Health Organization divides BMI into the following
categories for both men and women: underweight (18.5 or lower), normal
(18.5 to 24.9), overweight (25 to 29.9) and obese (30 or greater). A
BMI calculator is available on the National Institutes of Health Web
site at
http://nhlbisupport.com/bmi/bmicalc.htm.
"This
finding certainly shouldn't be an exercise disincentive for obese
women," McTiernan cautioned. "There are many benefits for women of any
weight to start exercising, like reducing their risk of heart disease
and diabetes. But in terms of breast-cancer risk, obese women will see
most benefit once they start getting their weight down."
Weight
plays a role in breast cancer, researchers believe, because fatty
tissue produces hormones and growth factors, such as estrogen and
insulin, which may promote cancer development.
"We think
that exercise works to lower cancer risk by lowering body fat, which
in turn lowers the levels of circulating cancer-promoting hormones. So
even if a woman is exercising, if she's overeating and her body fat
stays high, she's not going to get the same cancer-fighting protection
as a woman with less body fat."
The best
fat-burning formula involves low- to moderate-intensity exercise that
is done over a longer period as opposed to short, intense bursts of
activity, McTiernan said. "The bottom line is that duration of
activity is more important than intensity. The turtle beats the hare
when it comes to preventing breast cancer through exercise."
To get
the optimum breast-cancer protection, women should aim for at least 30
minutes of moderate-intensity exercise a day, five days a week, she
said, stressing that sedentary women should start gradually and work
their way up to the recommended minimum activity level.
"For
most, walking is probably going to be the easiest thing to do because
it doesn't require training or special equipment, just a good pair of
shoes. The main thing is for women to just get out there and do it,
and make it something they enjoy," said McTiernan, also a research
professor at the University of Washington School of Medicine and
School of Public Health and Community Medicine.
Investigators from the University of Washington, University of South
Carolina, Howard University, University of Massachusetts and the
Centers for Disease Control and Prevention collaborated on the study,
which was funded by the National Institutes of Health.
The study
involved an ethnically and racially diverse group of more than 74,000
postmenopausal women nationwide; 15 percent of participants were
minorities. In comparing whites and African-Americans, the study's two
largest racial groups, the researchers found both groups benefited
equally regarding the impact of exercise on breast-cancer prevention.
The study
participants were part of the Women's Health Initiative Observational
Study, an arm of WHI that is following women over time to identify
predictors of disease. The women were tracked for nearly five years to
examine the association between current and past recreational physical
activity and the incidence of breast cancer.
The
women, recruited through 40 WHI clinic sites nationwide, were surveyed
about their exercise history at ages 18, 35 and 50, as well as their
level of physical activity when they enrolled in the study (between
ages 50 and 79).
"When we
looked at the women's total activity throughout their adulthood,
including light, moderate and strenuous exercise, and added it all
together, those with the highest total amount of activity seemed to be
the most protected. It wasn't necessarily important regarding how much
of that activity was strenuous," said McTiernan, a WHI co-investigator
who directs clinical-outcomes efforts at the WHI Clinical Coordinating
Center, which is based at Fred Hutchinson.
WHI, one
of the largest prevention studies ever conducted in the United States,
focuses on prevention strategies for heart disease, osteoporosis, and
breast and colorectal cancer in postmenopausal women. Established in
1991 by the NIH, final results are expected in 2005.
# # #
The Fred
Hutchinson Cancer Research Center, home of two Nobel Prize laureates,
is an independent, nonprofit research institution dedicated to the
development and advancement of biomedical research to eliminate cancer
and other potentially fatal diseases. Fred Hutchinson receives more
funding from the National Institutes of Health than any other
independent U.S. research center. Recognized internationally for its
pioneering work in bone-marrow transplantation, the center's four
scientific divisions collaborate to form a unique environment for
conducting basic and applied science. Fred Hutchinson, in
collaboration with its clinical and research partners, the University
of Washington and Children's Hospital and Regional Medical Center, is
the only National Cancer Institute-designated comprehensive cancer
center in the Pacific Northwest and is one of 39 nationwide. For more
information, visit the center's Web site at www.fhcrc.org.
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