Research appearing in the August 20, 2003 issue of the Journal of the National Cancer Institute, has found the link between breast cancer and obesity in post menopausal women. It has long been known that there was an increase in breast cancer risk in obese women, this study explains why.

High levels of estrogen also increase the risk of breast cancer. The researchers analyzed blood from over 2,200 cancer-free women from around the world. During the following 12 years, 624 women developed breast cancer. Hormone levels were compared to the women who did not get cancer, as well as the body mass index (BMI—a way to measure obesity). They found that a high BMI (obese) was associated with an increased risk for cancer, but lower levels of estrogen mitigated that risk. The researchers believe that the increase in breast cancer risk with increasing BMI among postmenopausal women is largely the result of the associated increase in estrogens, particularly bioavailable estradiol.