Can selenium ward off deadly cancers?

Doctors from several medical centers teamed up to discover whether a diet enriched with the element selenium would prevent skin cancer. It did not. Had this been their sole interest, they might have declared the effort a flop. But the researchers also tallied the other cancers that subsequently afflicted their volunteers-and drew a surprising conclusion.

A group that swallowed daily selenium supplements had lower rates of several other cancers, including cancer of the lung, colon, rectum, and prostate, compared to a group that did not take the supplements. Moreover, selenium cut the combined death rate from these fearsome cancers by 50 percent.

"This is the first study to show that nutritional supplements in a Western population reduce the incidence and death rate from cancer," says team member Larry C. Clark of the University of Arizona College of Medicine in Tucson. "It opens a new era in cancer prevention research."

The research was prompted by two smaller studies showing that people with low blood concentrations of selenium are more likely than average to develop skin cancer. A third study found that U.S. counties where diets are naturally rich in selenium report lower death rates from a variety of cancers than those where dietary selenium is scarce.

Intrigued by these findings, the team examined the effect of adding 200 micrograms of selenium daily-triple the U.S. recommended allowance but well below the toxic dose-to the diets of people with skin cancer.

The 1,312 volunteers were patients sometime between 1983 and 1991 at seven dermatology clinics in low-selenium areas of the United States. For 4.5 years, one group took selenium and the other was given a placebo. Clark and his colleagues tracked the groups' progress for an additional 6 years.

By last January, approximately the same number of new skin cancers had emerged in the two groups. The nearly 200 other new cancers, however, followed a strikingly different pattern. 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 results, reported in the Dec. 25 Journal of the American Medical Association (JAMA), convinced the researchers to urge people in the placebo group to take selenium.

"We were surprised that we weren't able to affect the incidence of skin cancer," Clark says. He observes that the study may not have lasted long enough to see a change.

Often skin cancers develop only after many years from premalignant growths triggered by prior ultraviolet exposure. Volunteers in the study may have begun taking selenium too late to prevent the consequences of this early damage, he argues.

Graham A. Colditz of Harvard Medical School cautions in a JAMA editorial-and Clark agrees-that doctors should confirm the results in further studies before urging widespread use of selenium supplements.