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Beta-Carotene Can Cut Risk of Prostate Cancer

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WebMD Health News

Nov. 22, 1999 (New York) -- Men with low levels of beta-carotene in their blood can reduce their risk of prostate cancer by as much as 32% by taking beta-carotene supplements every other day, report Boston researchers in the Nov. 1 issue of the journal Cancer. Men with the lowest blood levels of beta-carotene at the start of the study had the greatest reduction in risk. Beta-carotene is converted into vitamin A by the body. In addition to its supplement form, beta-carotene can also be found in many fruits and vegetables such as carrots, squash, yams, peaches, apricots, spinach, collard or mustard greens, and broccoli.

Support for beta-carotene as an anticancer agent has been uneven, with at least two large studies showing an increase in lung cancer in people that received beta-carotene supplements. However, another study from the Boston researchers reporting the new data found no harm, but no significant benefit either. Other studies, notably the Chinese Cancer Prevention Trial, found a reduced incidence of stomach cancer and mortality in a poorly nourished population given a combination of beta-carotene, vitamin E, and selenium.

The latest data from the Physicians' Health Study, reported by Nancy R. Cook, ScD of Brigham and Women's Hospital and Harvard Medical School, support the hypothesis that beta-carotene may protect against prostate cancer occurrence in some men. In the study, almost 15,000 male physicians participated in the study, which was a large study of male physicians that began in 1982. The men received either beta-carotene or a placebo.

Over the 12 years of study, close to 1,500 men were diagnosed with cancer, including 631 with prostate cancer. Blood samples from these men were compared with those of over 2,000 men who did not take beta-carotene supplements. Men with the lowest blood levels of beta-carotene at the start of the study who took supplements had a 32% reduction in risk of prostate cancer. Beta-carotene supplements did not affect the risk of prostate cancer in men who had higher blood levels of beta-carotene at the beginning of the study.

Like other antioxidants, beta-carotene may prevent cancer-causing substances from damaging genetic material in cells. While this may be one explanation for its beneficial effect, Cook and colleagues write, the differing results of the various studies point to a need for more research with longer follow-up of patients receiving beta-carotene supplementation.

In an accompanying editorial, an Ohio researcher says the new study provides a foundation for further research into the role of various factors, including dietary antioxidants and family history, that converge to increase an individual's risk of cancer.

"What is clear is that no single study population or approach is adequate to provide a complete picture of the complex interactions between dietary antioxidants in foods," writes Steven K. Clinton, MD, PhD, of The Ohio State University in Columbus.

Clinton says physicians should exercise caution when advising patients about beta-carotene supplementation for cancer prevention, making certain to emphasize the importance of healthy dietary and lifestyle patterns coupled with effective detection. Tests used to detect prostate cancer include the rectal exam and the prostate-specific antigen (PSA) blood test. The American Cancer Society estimates that in 1999, nearly 180,000 men will be diagnosed with prostate cancer, and 37,000 will die.

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