Soy Protein Lowers Estrogens Associated With Breast Cancer

The study found a link between soy-rich diets consumed by Asian women in Singapore and reduced levels of an estrogen called estrone, the predominant form of estrogen in women following menopause.

Consuming tofu and other soy-based foods significantly lowers levels of a class of estrogens normally associated with breast cancer risk in postmenopausal women, according to a new study published in the September issue of the American Association for Cancer Research (AACR) journal, Cancer Epidemiology, Biomarkers & Prevention.

The study found a link between soy-rich diets consumed by Asian women in Singapore and reduced levels of an estrogen called estrone, the predominant form of estrogen in women following menopause. High estrogen levels have been shown to increase the risk for breast cancer among postmenopausal women.
Specifically, the study found that estrone levels were about 15 percent lower among women who consumed the highest amounts of soy protein. No other easily modifiable lifestyle factors analyzed by the scientists yielded such a dramatic hormone reduction.

"Results from this study support the hypothesis that high soy intake may reduce the risk of breast cancer by lowering endogenous estrogen levels, particularly estrone," said Anna H. Wu, the study's lead investigator and professor of preventive medicine at Keck School of Medicine of the University of Southern California, Los Angeles, Calif.

Isoflavones, the main constituent of soybeans, are believed to be responsible for anti-cancer effects observed in an accumulating number of human and animal studies.

"However, the effect of soy on the breast is controversial," said Dr. Wu. "There are some in vitro studies of breast cancer cells -- animal studies, as well as short-term soy intervention studies in women -- suggesting that soy isoflavines may have stimulatory effects."

Added Dr. Mimi Yu, principal investigator of the Singapore Chinese Health Study and a professor of preventive medicine at the Keck School of Medicine at USC: "Though our study is suggestive, more work needs to be done before any specific dietary recommendations can be made about consuming soy proteins to protect against breast cancer."

Founded in 1907, the American Association for Cancer Research (AACR) is a professional society of more than 19,000 laboratory and clinical scientists engaged in cancer research in the United States, Canada, and more than 60 other countries. AACR's mission is to accelerate the prevention and cure of cancer through research, education, communication and advocacy. Its scholarly activities include the publication of five journals (Cancer Research, Journal of Clinical Oncology, Molecular Cancer Research; Cancer Epidemiology, Biomarkers & Prevention; and Molecular Cancer Therapeutics). AACR's annual meeting has more than 15,000 participants and features presentations of new and significant discoveries in the cancer field. AACR's 10 specialty meetings cover all of the important areas of basic, translational and clinical cancer research.

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