Selenium's Surprising Anticancer Power

In a stunning finding, daily supplements of the trace element selenium have been found to reduce the risk of several types of cancer in patients with a history of skin cancer. The results, reported in tomorrow's issue of the Journal of the American Medical Association, surprised researchers, who are discouraging people from loading up on the supplement until the results are reproduced in other people.

A team led by epidemiologist Larry Clark of the Arizona Cancer Center in Tucson had observed lower rates of skin cancer among people with high levels of selenium. So the group set out to test whether selenium might reduce the chance of recurrence of basal cell or squamous cell carcinoma in people previously treated for skin cancer. Beginning in 1983, they began to enroll patients from seven dermatology clinics in the eastern United States, giving half the group a daily placebo and the other half 200 micrograms of selenium in a brewer's yeast tablet. A total of 1312 patients, three-fourths of them men, were given selenium or the placebo for an average of 4.5 years.

The group found that the selenium was no better than the placebo at preventing a skin cancer comeback, thus disproving the initial thesis. But it did demonstrate some anticancer properties. For example, the selenium group recorded only 77 cases of secondary cancer compared with 119 in the control group. For prostate cancer, the ratio was 13 cases versus 35; for colorectal cancer, eight versus 19; and for lung cancer, 17 versus 31. The selenium group also experienced 17% fewer deaths, including half as many as controls from a variety of cancers. The trial was scheduled to continue for 2 more years, but Clark pulled the plug early "so that physicians could know of this cancer-prevention potential."

Experts say the findings should be viewed with caution. The study is "very, very encouraging," says Clement Ip, a cancer researcher at Roswell Park Cancer Institute in Buffalo, but he and others say more studies are needed to determine how selenium acts on tumors and how it affects a broader spectrum of patients. There are also questions about its safety when taken on a long-term basis: Selenium can lead to a loss of hair and nails at doses larger than 1 milligram. "We're recommending that we do an additional trial to confirm these results and see how it would extend to other populations," says Clark, in particular women and those with certain cancer types.