by

Charles A. Bertrand, M.D., FACP, DIM-CD (Ret.)
Associate Clinical Professor of Medicine at New York Medical College
and at the Medical University of South Carolina

SELENIUM - DOES IT PREVENT CANCER?

An intriguing study of cancer treatment appeared recently in the Journal of the American Medical Association, Vol. 276, No. 24, pp. 1957-1963 (December 25, 1996). This study – reported by L. C. Clark, M.PH., Ph.D., G. F. Combs, Jr., et al – focused on the question of whether or not the use of selenium would decrease the incidence of skin cancer. A total of 1,312 patients with a history of this disease were observed during a period from 1983 through 1991. About half the patients orally received pills of 200 mg of selenium per day, while the others were given a placebo (a pill that looked like selenium but did not contain the medicine).

The researchers reported no reduction in skin cancer among the patients who received selenium – a negative study.

However, the researchers in 1990 also began looking at the effect of selenium on all causes of mortality, including other forms of cancer. In these cases, they found some positive results.

Total number of deaths from cancer appeared to be reduced in the selenium group, with 29 deaths as opposed to 57 deaths among patients who took the placebo. In fact, the total number of cancers among patients on selenium totaled 77, while the figure was 119 among those who did not receive selenium. This difference occurred in lung cancer, colon and rectal cancers, and in prostate cancer. (In no case did selenium cause toxic side effects). Within a week press reports in the media heralded this new method of preventing cancer, based on this single report. <

So what should we make of this study?

For one thing, only 25 percent were female, so we can't draw any definite conclusions about the effect of selenium on women. The numbers are simply too small. As a matter of fact, there were nine breast cancers in the selenium group, as opposed to three in the placebo group, but this was not considered "statistically significant."

The study does raise an obvious question: Why does selenium seem to affect the development of certain forms of cancer and not others? At present, this remains an intriguing mystery.

Selenium has been studied over a period of 30 years, and the results have been mixed. In fact, several recent researchers have concluded that selenium has no effect on retarding or preventing the development of cancer, though one study involved a much lower dosage, which may explain why their results were inconclusive.

An editorial comment on this article (in the same issue of the Journal of the American Medical Association) said: "As in clinical trials, decisions are best made when a number of studies show consistent findings."

This is saying the obvious. Clearly what we need are more and larger studies in which patients are monitored over a longer period of time. Four and a half years is a relatively short period. Perhaps over ten years the picture will be clarified.

Then, too, 1,312 patients may seem like a lot to the layman, but in medical research it is a relatively small sample. For example, I did a study on electrocardiograms for IBM several years ago involving 25,000 EKG's, half of which were interpreted by computer, half of which I analyzed myself. The conclusions were more persuasive because of the large sample involved.

So should doctors immediately begin to prescribe daily doses of selenium? The results are still inconclusive. One thing, however, is clear. Taking selenium would not eliminate the need for older men to have a regular prostate examination as well as a blood test (PSA) to detect this particular kind of cancer. And anyone with a family history of rectal or colon cancer should be checked periodically. So should long-term smokers.

As for selenium as a preventative treatment, the jury is still out. Certainly we should follow future studies with great interest. But it would be foolish at present to conclude that taking selenium is sufficient to deter these four types of cancer. Stick to established preventative procedures until someone comes up with a definitive study. Unfortunately, this isn't it.

The advice provided on this website is intended to be general in nature and should not be relied upon for specific treatment. If you need personal medical attention please contact your physician.

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