Obesity Increases Breast Cancer Risk
Belly Fat, Hip Fat -- All Body Fat Increases Risk
May 17, 2004 -- Overweight postmenopausal women have a
one-third higher risk of breast cancer, according to new research. Whether
she's apple or a pear shaped -- whether she has belly fat or hip fat -- an
overweight woman past menopause is at high risk.
This extensive study, which involved nearly 175,000 women in
nine European countries, appears in the latest issue of the International
Journal of Cancer.
It is more evidence that obesity and breast cancer risk are
indeed linked, writes lead researcher Petra H. Lahmann, PhD, an epidemiologist
with the German Institute of Human Nutrition in Nuthetal.
"This is the largest study thus far confirming this
pattern," Padma Nadella, MD, a medical oncologist with the Winship Cancer
Institute at Emory University School of Medicine in Atlanta, tells WebMD.
"Whether it's hip or belly fat, it's obesity that increases
breast cancer risk," says Nadella. "The increased fat in your body
increases estrogen in postmenopausal women. When you develop breast cancer, it
appears that it is due to excess estrogen produced by body fat."
Body Fat and Breast Cancer
Indeed, there have been uncertainties about the role that a
woman's body size plays in her breast cancer risk, Lahmann writes. Body fat and
menopause have seemed to be important factors.
Scientists believe that body fat causes the body to produce
more estrogen than necessary. There is substantial evidence that high
concentrations of estrogen are associated with increased risk of postmenopausal
breast cancer, Lahmann writes. Studies have also shown that the estrogen in
hormone replacement therapy (HRT) may increase breast cancer risk.
Confirming Risks From Obesity, HRT
Lahmann's study involved 176,886 European women between 18 and
80 years old living in France, Italy, Spain, Great Britain, the Netherlands,
Greece, Germany, Sweden, and Denmark.
At the study's beginning, the women had a variety of
measurements taken -- height, weight, body mass index (or BMI, a measure of
body fat), waist size, and hip circumference. They also completed food and
lifestyle questionnaires, including whether they took hormone replacement
Researchers then factored in the women's breast cancer
diagnoses over an almost five-year period. They found 1,879 cases of invasive
Among postmenopausal women:
- Weight at the start of the study was the strongest predictor of the risk of
breast cancer. The researchers found a 65% increase in the risk of breast
cancer for women in the highest weight category compared with women in the
lowest weight category.
Being overweight or obese (a BMI of more than 25) was a strong
risk factor for breast cancer -- increasing risks by more than 30%.
Among women who had used hormone replacement therapy (HRT)
during the study period, body fat was inversely associated with the risks of
breast cancer. In other words, the researchers showed that obese postmenopausal
women who were using HRT had a 34% reduction in breast cancer risk, compared
with lean women.