May 1 (HealthDay News) -- Despite earlier promise, three nutrients - vitamin E, selenium and soy - do not seem to prevent prostate cancer in men with precancerous prostate lesions, Canadian researchers report.
"There has been a collection of scientific data that has suggested that these agents could have a tremendous impact in preventing prostate cancer," said lead researcher Dr. Neil E. Fleshner, a Clinical Studies Resource Centre Member at the Ontario Cancer Institute and Love Chair in Prostate Cancer Prevention at the University of Toronto.
"So there was great hope that this would be a magic bullet that would help prevent prostate cancer," he said. "Unfortunately, it doesn't appear to be so."
The report was to be presented Sunday at the American Urological Association's annual meeting, in Chicago.
For the study, Fleshner's team randomly assigned 303 men with high-grade prostatic intraepithelial neoplasia (precancerous lesions) to receive soy protein, vitamin E and selenium, or a placebo. Over three years, the men had several biopsies to determine if they had developed prostate cancer.
Just over 26 percent of the men did develop invasive prostate cancer. However, the three nutrients did not seem to minimize that risk, the team found.
"To recommend soy and these supplement to men with high-grade prostatic intraepithelial neoplasia really doesn't make much sense, if the reason you are giving it is to prevent your patient from developing invasive cancer," Fleshner concluded.
He did leave the door open to using these supplements to prevent prostate cancer before precancerous lesions have formed. "In pre-cancer, the cells may already be so damaged that supplements can't reverse the changes," he reasoned. "Or maybe it just doesn't work."
The results confirm the findings of the two recent prospective trials, which also found that vitamin E, vitamin C and selenium do not prevent prostate cancer. The results of these trials were published in the Jan. 7 issue of the Journal of the American Medical Association. Other recent studies have suggested that vitamins, B, C, D, E, folic acid and calcium taken alone, or in various combinations, aren't effective for cancer prevention.
"Single-agent interventions, even in combinations, may be an ineffective approach to primary prevention in average-risk populations," wrote Dr. Peter Gann, author of an accompanying Journal of the American Medical Association editorial.
However, one expert believes that while vitamins E and C may not prevent prostate tumors, soy might still prove to be of benefit.
"There is some evidence from laboratory and population studies that soy protein or its components might reduce risk of prostate cancer," said Eric Jacobs, strategic director for Pharmacoepidemiology at the American Cancer Society.
In this study, soy protein had no apparent effect on the development of prostate cancer among men who already had precursor lesions in the prostate, Jacobs noted. "However, it remains possible that soy could reduce risk of developing prostate cancer by inhibiting earlier stages of prostate cancer development, or that soy could reduce the risk of recurrence or disease spread in men with prostate cancer," he said.
Douglas MacKay is vice president for Scientific & Regulatory Affairs at the Center for Responsible Nutrition, which represents the supplements industry. He believes the role of supplements is complex and trying to find a pill that will prevent cancer is a hopeless task. However, supplements and a healthy lifestyle can both play a role in helping patients prevent or fight cancer, MacKay said.
"Soy isoflavones and other dietary supplements may help prevent the development of cancer," MacKay said. "Men should include these things as part of a healthy lifestyle and integrated approach to preventive medicine. However non-pharmacologic dietary preventions, whole foods, extracts and herbs' influence on the development of cancer is complex and may not be appropriately tested using a randomized clinical trial."
SOURCES: Neil E. Fleshner, M.D., M.P.H., Clinical Studies Resource Centre Member, Ontario Cancer Institute, Love Chair in Prostate Cancer Prevention, University of Toronto, Canada; Eric Jacobs, Ph.D., strategic director, Pharmacoepidemiology, American Cancer Society; Douglas MacKay, N.D., vice president, Scientific & Regulatory Affairs, Center for Responsible Nutrition, Washington D.C.; April 26, 2009, presentation, American Urological Association annual meeting, Chicago