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Stanford Report, October 3, 2001

Study shows compound in broccoli may lower risk of prostate cancer


Studies in recent years have shown that eating broccoli seems to lower the risk of prostate cancer. Now a new study from Stanford University Medical Center points to a possible secret ingredient -- the compound sulforaphane.

James D. Brooks, MD, assistant professor of urology, and colleagues conducted a study in which they found that sulforaphane, a compound abundant in broccoli, appears to increase enzymes that buttress cellular defenses against prostate cancer. The enzymes seem to protect against prostate cancer by deactivating cancer-causing chemicals, such as DDT, that infiltrate the body. Sulforophane belongs to a class of food compounds known as phytochemicals, which are active substances that are components of plants. Brooks' study was published in the September 2001 issue of Cancer Epidemiology, Biomarkers and Prevention.

A 1994 study published by Brooks and colleagues in the Proceedings of the National Academy of Sciences showed that in the earliest stages of prostate cancer, malignant cells lose an enzyme critical to defending against cancer-causing agents.
Additionally, a study published in August 2000 by Alice Whittemore, PhD, professor and chief of Stanford's division of health research and policy, and her colleagues showed that people who eat large quantities of broccoli have a reduced risk of cancer. "But that study and others didn't indicate which of hundreds of ingredients in broccoli might offer protection," Brooks said.

Brooks cautioned that more work is needed before people rush to add sulforaphane supplements to their diets. He emphasized that his study was conducted in lab cultures, not in human or animal subjects. "While we have pretty convincing evidence that broccoli may protect against prostate cancer -- and that sulforaphane is the primary ingredient -- we can't automatically assume that this ingredient in isolation will work," he said. "For example, we don't know if sulforaphane must work in conjunction with some other ingredient in broccoli to be effective or even safe."

Brooks said the study brings researchers closer to a strategy that might protect against prostate cancer, the No. 1 form of cancer affecting men and the second-leading cause of cancer deaths among men. The American Cancer Society predicts that this year alone, 198,000 new cases of prostate cancer will be diagnosed in the United States and nearly 32,000 men will die of the disease.

Brooks' study was supported by a U.S. Department of Defense New Investigator Award and by a Doris Duke Clinician Scientist Award.

Other authors include two students in Brooks' lab: Vincent G. Paton, currently working for an area biotech firm, and Genevieve Vidanes, now a PhD student at UCSF.