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Body Mass Index Associated With Breast Cancer, Regardless of Body Shape

Study may clarify association between obesity and breast cancer

A study of predominantly Caucasian women finds a larger waist circumference is associated with a higher risk of post-menopausal breast cancer, but not beyond its contribution to BMI. The study, by researchers at the American Cancer Society, fails to confirm previous findings that body shape itself is an independent risk factor for breast cancer.

The new study was published in the April 2014 issue of Cancer Causes & Control.

Research has linked abdominal obesity to several conditions, including heart disease, type-2 diabetes, and breast and other cancers. Those studies have led to the theory that having an “apple-shaped” body, with weight concentrated in the chest and torso, is riskier than having a “pear-shaped” body, with fat concentrated in the hips, thighs and buttocks.

To explore the theory, researchers analyzed data from 28,965 women participating in the Cancer Prevention Study II. Among these women, 1,088 invasive breast cancer cases were diagnosed during a median follow-up period of 11.6 years.

The researchers found that, without adjustment for BMI, a larger waist circumference was associated with a higher risk of breast cancer (per 10-cm increase in waist circumference; hazard ratio [HR], 1.13). However, adjustment for BMI eliminated the association with waist circumference (per 10 cm; HR, 1.00).

“The message is that if you have a high BMI, regardless if you are pear- or apple-shaped, you are at higher risk of breast cancer,” said lead investigator Mia Gaudet, PhD. “Most prior studies on this issue looked at BMI or at waist circumference, but had not looked at them together. This study brings some clarity to the association between obesity and risk of breast cancer.”

Gaudet said the data could help women focus on what’s important in what has been a confusing array of potential risk factors for breast cancer. “We know being overweight — particularly when the weight gain happened during adulthood — is one of the important modifiable risk factors for breast cancer in post-menopausal women. These new data indicate it’s not what shape you are, it’s what kind of shape you are in that probably ought to be their focus.”

Sources: EurekAlert; April 16, 2014; and Cancer Causes & Control; April 2014.

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