A high dietary intake of the mineral selenium may reduce the risk of prostate cancer by as much as two-thirds.

By measuring the amount of selenium found in men's toenail clippings, Dr. Kazuko Yoshizawa and colleagues from the Harvard School of Public Health found that those who had prostate cancer had significantly lower levels of the nutrient than those without the disease. The amount of selenium secreted by the body in the toenails is a measure of overall selenium intake in a person's diet, the researchers stated.

The study, published in the current issue of the Journal of the National Cancer Institute, backs up previous research showing that increasing daily intake of selenium and vitamin E may help reduce the risk of advanced-stage prostate cancer. Selenium and vitamin E have been shown to work together in the body to produce antibodies that boost the immune system.

Larger trials are now needed to determine if selenium and/or vitamin E can reduce the risk of cancers, heart disease, stroke and death from any cause, said Dr. Philip R. Taylor of the National Institutes of Health in Bethesda, Md. In an editorial accompanying the Harvard study, Taylor said another important issue still to be determined is the level of selenium considered to be safe. Selenium is known to be toxic in high doses.