Nutrition Research News
CHICAGO Selenium supplements are not effective for preventing skin cancer but may help protect against cancers of the lung, colon and rectum, and prostate, according to an article in this week's issue of The Journal of the American Medical Association (JAMA).
Larry C. Clark, M.P.H., Ph.D., from the Arizona Cancer Center, College of Medicine, University of Arizona, Tucson, and colleagues studied the effectiveness of selenium supplementation for preventing development of new basal cell carcinoma (BBC) and squamous cell carcinoma (SCC) of the skin. A total of 1,312 patients with previous skin cancers received placebo or 200 micrograms of the trace element selenium per day for a mean of 4.5 years and a total follow-up of 6.4 years. The patient population was recruited from the Eastern Coastal plain of the U.S., an area with relatively low selenium levels in soil and crops and also high rates of BBC and SCC.
The researchers found that selenium supplementation did not reduce the incidence of BBC or SCC. However, midway through the study, the authors also decided to evaluate the effect of selenium for preventing other types of cancers and for reducing cancer mortality. These secondary results indicate that when all cancers were studied, the selenium group had a 37 percent reduction in cancer incidence and a 50 percent reduction in cancer mortality, although there were no significant differences in deaths from all causes in the selenium group or the placebo group.
Of the nearly 200 new cases of cancer diagnosed, the selenium group had 63 percent fewer prostate cancers, 58 percent fewer colorectal cancers and 46 percent fewer lung cancers than the placebo group.
The authors write: "Primarily because of the apparent reductions in total cancer mortality and total cancer incidence in the selenium group, the blinded phase of the trial was stopped early. No cases of selenium toxicity occurred."
"They continue: "These apparent beneficial effects of selenium supplementation require confirmation in independent trials of appropriate design before public health recommendations regarding selenium supplementation can be made."
The researchers add that the selenium dose of 200 micrograms per day is within the normal dietary intake of Americans and provides approximately twice the projected typical dietary intake of the study patients.
Information cited in the study shows that selenium was first associated with cancer risk in the late 1960s. Hypotheses explaining selenium's inhibition of tumor growth include antioxidant properties; the ability to alter carcinogen metabolism; effects on the endocrine and immune systems; and inhibition of protein synthesis.
Selenium and Cancer Prevention: Promising Results Indicate Further Trials Required
In a related editorial in the same issue of JAMA, Graham A. Colditz, M.B.B.S., Dr.P.H., Brigham and Women's Hospital and Harvard Medical School, Boston, Mass., sounds a strong note of caution about the study and its findings. He pointed out several major concerns, including questions about the biological plausibility of the rapid and large effects observed, issues related to the interpretation of endpoints for cancer mortality and total cancer incidence (which were established well after the trial was underway), and limited applicability of the results for women.
Dr. Colditz writes: "This promising set of results ... require confirmation in further randomized trials designed to test the effect of selenium supplementation on cancer incidence and mortality ... For now it is premature to change individual behavior, to market specific selenium supplements, or to modify public health recommendations based on the results of this one randomized trial."
He continues: "As we await the results of further prevention research, known lifestyle changes that can reduce cancer risks (such as smoking cessation, consuming adequate amounts of fruits and vegetables each day, reducing intake of animal fat, and increasing physical activity) should be implemented."
This study was funded in part by grants from the American Institute of Cancer Research, the American Cancer Society, the National Institutes of Health, and Nutrition 21, La Jolla, Calif.
Reporters seeking interviews may contact:
- Larry Clarke, Ph.D., MPH, principal investigator
associate professor of epidemiology, Arizona Cancer Center
- Bruce Turnbull, Ph.D., biostatistics director
Director of Statistics Center, Cornell University, Ithaca, NY
- Gearald Combs, Ph.D., laboratory director
Professor of Nutrition, Cornell University, Ithaca, NY
Abstracts from JAMA and the AMA's Archives journals are available on the AMA's web site (http://www.ama-assn.org).
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