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STUDY SUGGESTS HOW SOY CONSUMPTION MAY REDUCE BREAST CANCER RISK

GALVESTON -- A study at the University of Texas Medical Branch at Galveston suggests that soya consumption may reduce breast cancer risk by lowering a woman's female hormone levels.

Population-based studies have shown that soybean consumption is associated with reduced risk for breast, prostate and colon cancers.

"Our studies seek to understand how soya diets prevent breast cancer development," said Lee-Jane W. Lu, Ph.D., lead investigator of the study, who presented her results April 12 during the 90th annual meeting of the American Association for Cancer Research in Philadelphia. "Soybeans contain a significant quantity of estrogen-like compounds called isoflavones. These isoflavones have been shown in animal models and in tissue cultures to be weak estrogens."

These weak estrogens are also called "phytoestrogens" (meaning estrogenic compounds derived from plants). Research has shown that they inhibit cell growth and blood vessel formation and induce cells to differentiate.

High levels of ovarian steroids have been postulated to be risk factors for developing breast cancer. People from areas with low risk for breast cancer, such as Asia, produce lower levels of ovarian hormones than people residing in areas, such as America, with a high risk for breast cancer. Breast cancer patients produce higher endogenous levels of estrogens than non-breast cancer subjects. Thus, the experts in the field generally believe that lowering a woman's endogenous estrogens can lower their breast cancer risk.

The UTMB researchers examined the relationship of soybean consumption and ovarian steroid hormones in premenopausal women from the Galveston area. Over the past five years, they have conducted three different soya feeding studies. Each study involved a separate group of six to ten regularly cycling women who were not on contraceptives during the studies. Within one to six days after their menses started, women began to ingest soymilk daily for one to five menstrual cycles. Their blood hormone levels were measured while they were consuming their own home diets, during the time they were ingesting soymilk, and after they stopped ingesting soymilk.

The UTMB team found that blood levels of measured estrogens were reduced by 30-40 percent in women who consumed soybeans. This finding led them to conclude that women who consume soybeans reduce their circulating levels of estrogen.

The results from all three studies showed that ovarian hormone levels were the lowest while women were consuming soymilk.

"The implication of our research results is that soya diets may be useful for preventing breast cancer," Lu said. "More studies will be needed to understand how much and how often one should consume soya foods."

The research was conducted in the UTMB Department of Preventive Medicine and Community Health and UTMB General Clinical Research Center. It was funded by National Cancer Institute and the National Institutes of Health program for General Clinical Research Centers, the American Institute for Cancer Research, and the John Sealy Memorial Endowment.

The research team also included Manubai Nagamani, M.D., Karl E. Anderson, M.D., and James J. Grady, Dr. P.H.

-UTMB-