National Pilot Study To Test Whether Soy Can Reduce Prostate Cancer Risk

March 09, 1999

WINSTON-SALEM, N.C. -- Investigators at Wake Forest University School of Medicine will provide scientific leadership for a national pilot study to test whether soy will reduce the risk of prostate cancer.

"In Asian countries like Japan, where soy consumption is high, prostate cancer rates are lower than in Western countries with low soy intake," said Electra D. Paskett, Ph.D., associate professor of public health sciences (epidemiology) and principal investigator, in explaining the rationale for the study.

She said the pilot study of 160 men would evaluate the effect of soy on markers for prostate cancer risk. "We do not know conclusively how soy will affect the prostate," she said.

The $494,588 study, being funded by the U.S. Department of Defense, is one of the research projects of the newly funded Center of Excellence in Prostate Cancer at the Medical Center.

Paskett noted that soybeans and other legumes contain large amounts of plant estrogens known as isoflavones. Both laboratory studies and epidemiological studies have identified several isoflavones found in soy products -- genistein and daidzein -- as reducing breast, colon and prostate cancer. Genistein and daidzein also have been shown to possess cholesterol- lowering properties that help reduce the risk of heart disease and other cardiovascular diseases.

The study will involve 160 men, half African-American, between the ages of 55 and 70 who have high levels of prostate-specific antigen on the PSA test, but who have normal prostate biopsies, she said. The trial will measure the effect of the soybean supplements on clinical markers -- such as changes in the PSA level and the size of the prostate -- and other signs of prostate cancer risk.

They'll also be measuring the effect of the soy protein on blood pressure, hormone levels, levels of cholesterol and lipoproteins, such as high density lipoproteins (HDL) and low density lipoproteins (LDL), the good and bad cholesterols.

The study also will look at the effects of soy on urinary and sexual functioning and on overall quality of life.

The participants will be randomly assigned to one of two groups, one that will get a soy protein dietary supplement and another that will get casein (milk) protein supplement.

The study will be conducted through one of the major national cancer clinical trials cooperative groups, Cancer and Leukemia Group B, which is composed of 200 institutions from both academic medical centers and community hospitals. Investigators at four sites will facilitate recruitment.

Paskett said Wake Forest University School of Medicine was selected to provide the scientific leadership for the study based on the school's previous research by Gregory Burke, M.D., professor and interim chair of public health sciences and associate professor of neurology, and J. Mark Cline, D.V.M., Ph.D., assistant professor of pathology (comparative medicine) on soy supplementation and chronic disease, which have been widely reported. Both Burke and Cline are investigators on the new study, as are W. Robert Lee, M.D., associate professor of radiation oncology, and Mara Z. Vitolins, Dr. P.H., coordinator of the Nutrition Epidemiology Research and Applications Unit in the Department of Public Health Sciences.

"If positive results are obtained in this trial, soy supplementation may provide an important tool for the prevention of prostate cancer," Paskett said. "If effective, these compounds would be a powerful choice for general disease prevention."

Wake Forest Baptist Medical Center

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