Breast
Cancer Risk Lower for Heavier Young Women
Women who are heavier in young adulthood have a
lower risk of developing breast cancer before they reach menopause,
according to a report in the Archives of Internal
Medicine.
The study confirms and expands on previous research
suggesting that larger body size before menopause helps fend off breast
cancer.
Experts stress that this finding is not a license
for women to gain weight.
"We have to remind women that obesity is pretty
much bad for everything else and, as soon as you become postmenopausal,
obesity is one of the strongest predictors of breast cancer," says
Karin B. Michels, Sc.D., Ph.D., at Brigham and Women's Hospital in
Boston, Mass.
"It's never a good idea to be obese because of other
health effects," adds Dr. Jay Brooks, of the Ochsner Health System
in Baton Rouge, La.
"The problem is that women who are postmenopausal,
which is where the largest number of breast cancers are, have a very
hard time losing weight," says Dr. Brooks.
Recent research has shown that postmenopausal women
can cut their breast cancer risk by shedding extra pounds.
However, the situation is somewhat different for
younger, premenopausal women. In this group, prior studies had shown
that as body-mass index (BMI) went up, breast cancer risk declined.
Some had speculated that this was because a higher
BMI is associated with irregular or long menstrual cycles and the development
of polycystic ovary syndrome (PCOS) - all of which are associated with
problems in ovulation.
Ovulatory dysfunction, in turn, decreases levels
of estrogen and progesterone. Lower levels of these sex hormones -
long linked to breast cancer - could account for a lowered risk of
malignancy.
For this study, Dr. Michels and her colleagues tracked
outcomes for more than 113,000 premenopausal women who were part of
the Nurses' Health Study II, a group of female registered nurses who
have been followed by researchers since 1989.
The women were followed until 2003, or until they
developed breast or other cancer, died, or reached menopause, whichever
came first.
Women with a current BMI of 30 or higher (considered
obese) had a 19 percent lower risk of breast cancer compared with those
who had BMIs of 20 to 22.4 (in the normal range).
Women whose BMI at age 18 was 27.5 or higher (considered
overweight) had a 43 percent lower risk of developing breast cancer,
compared with women whose 18-year-old BMI was between 20 and 22.4.
"We have indeed seen this inverse association between
BMI and premenopausal breast cancer, but what's new is that the earlier
we go in a woman's life, the stronger that association becomes," explains
Dr. Michels. "BMI earlier in her life is more important than her more
immediate past."
The findings held true even after adjusting for
menstrual cycle patterns and infertility as a result of ovulatory disorder
such as polycystic ovary syndrome. The use of birth control pills was
also considered.
"We basically figured that ovulation was not an
explanation - which had been hypothesized before, but nobody had put
it to the test," says Dr. Michels.
So, the exact explanation for the weight-breast
cancer link in young women remains unclear.
"We don't really know what the explanation is," notes
Dr. Michels.
For now, the findings may be more pertinent to researchers
than to patients.
"It doesn't necessarily have clinical implications
other than to say that we want to be aware of earlier life and of the
importance of earlier life," says Dr. Michels.
"For researchers, it is important and interesting
to better understand premenopausal breast cancer, because it is not
very well understood, and it's increasing," she concludes.
Always consult your physician for more information.
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