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Obesity Increases Breast Cancer Risk

Belly Fat, Hip Fat -- All Body Fat Increases Risk

WebMD Health News

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 therapy.

Researchers then factored in the women's breast cancer diagnoses over an almost five-year period. They found 1,879 cases of invasive breast cancer.

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.

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