Sporten,
ook weinig, helpt tegen ontstaan borstkanker.*
Vrouwen
die vanaf hun 10e jaar gemiddeld iedere week 80 minuten wat aan sport
doen hebben 20% minder kans op het krijgen van borstkanker. Dit blijkt uit een
vergelijkend onderzoek onder ruim 9.000 Amerikaanse vrouwen. Men kon niet
vaststellen op het sporten op verschillende leeftijden nog verschil maakte. Wel
is al gebleken dat door het sporten van vrouwen de hoeveelheden hormonen zoals oestrogeen
als progesteron in het bloed verlaagden. Te hoge bloedwaarden van deze hormonen
kunnen aanleiding zijn tot het ontstaan van borstkanker. Verder
doet sporten de bloedsuikerspiegel
verlagen en de hoeveelheid vet afnemen, oorzaken waardoor ook de hoeveelheid
hormonen verlaagd worden en daardoor de kans op borstkanker.
Exercise
reduces breast cancer risk, even a little bit helps
Both
black women and white women who regularly exercise have a decreased risk of
breast cancer compared to women who do not exercise, according to researchers at
the Keck School of Medicine of the University of Southern California.
Numerous studies have linked physical activity to lower breast cancer risk in
white women, but the Keck School study-published in the Nov. 16 issue of the
Journal of the National Cancer Institute-extends the finding to black women.
"A growing body of evidence has linked recreational activity to lowered
breast cancer risk, but we really haven't known whether that lowered risk
applies to all subgroups of the population," says study lead author Leslie
Bernstein, Ph.D., AFLAC Chair in Cancer Research and professor of preventive
medicine at the Keck School. "This study indicates that exercise may be
just as much a modifiable risk factor among black women as it is among white
women."
Bernstein and her colleagues conducted the Women's Contraceptive and
Reproductive Experiences, or CARE, Study, a National Institutes of
Health-supported project. Researchers interviewed 4,538 black women and white
women between ages 35 and 64 who had been diagnosed with invasive breast cancer
in the mid-1990s, and matched them to 4,649 women without breast cancer. The
multi-center, case-control study had sites in Los Angeles, Atlanta, Seattle,
Philadelphia and Detroit.
The researchers asked the women about a variety of lifestyle factors that might
influence breast cancer risk, such as smoking habits, alcohol consumption, age
at first menstruation, number of pregnancies, use of oral contraceptives, and
more. They also asked about the types of physical activities women participated
in for at least an hour at week for at least four months a year-going back as
far as age 10, to develop a lifetime measure of each woman's exercise activity.
Popular activities included walking, aerobics and cycling.
Of the 4,538 women with breast cancer, 1,132 (about 25 percent) reported no
exercise activity since age 10. Of the 4,649 women who had not had breast cancer,
1,083 (about 23 percent) reported no exercise activity since age 10.
When researchers compared women who exercised to those who did not, they found
that women exercising at least 1.3 hours a week on average since age 10 had
about a 20 percent lower risk of breast cancer than women who were inactive.
This relationship held true for both black women and white women. Researchers
saw the relationship even after controlling for other factors such as body mass
index and reproductive history. However, physical activity did not decrease
breast cancer risk among women who had a family history of breast cancer,
suggesting that hereditary factors might interfere with or overpower the
beneficial effects of exercise.
Epidemiologists have sought to understand whether exercise is more beneficial at
certain ages than others; however, researchers in the Women's CARE Study did not
find any particular time of life when physical activity had a greater influence
on breast cancer risk.
Bernstein says that researchers have proposed several mechanisms under which
exercise might lower breast cancer risk.
For one, studies among serious athletes and recreational athletes show that
exercise activity can lower levels of female hormones circulating in the blood,
particularly estrogen and progesterone. This is particularly apparent during
adolescence and early adult years. Even postmenopausal women who exercise may
have lower estrogen levels. Researchers believe that higher circulating levels
of female hormones may raise breast cancer risk by stimulating breast cells to
divide and multiply.
Women who exercise regularly also appear to be more sensitive to insulin and
have lower levels of insulin in their blood. Higher concentrations of insulin in
the blood may result in higher levels of female hormones. In addition, women who
exercise are more likely to maintain normal body weight; excess fat is thought
to contribute to greater circulating levels of female hormones and
insulin-related hormones.
"Unfortunately, black women in the study were more likely than white women
to be inactive," Bernstein says. "Physical activity not only appears
to be associated with lower breast cancer risk, but has other widely known
health benefits, reducing the risk of cardiovascular disease and diabetes.
Increasing activity among black women may be an area of potential intervention
for better health."
The National Institute of Child Health and Human Development supported the study,
with additional support from the National Cancer Institute.
L. Bernstein, A. Patel., G. Ursin, J. Sullivan-Halley, M. F. Press, D. Deapen,
J.A. Berlin, J.R. Daling, J.A. McDonald, S.A. Norman, K.E. Malone, B.L. Strom,
J. Liff, S.G. Folger, M.S. Simon, R.T. Burkman, P.A. Marchbanks, L.K. Weiss and
R. Spirtas, "Lifetime Recreational Exercise Activity and Breast Cancer Risk
Among Black Women and White Women," Journal of the National Cancer
Institute. Vol. 97, No. 22, Nov. 16, 2005, pp. 1-9.
Kathleen O'Neil
University of Southern California
http://www.usc.edu (November
2005)
