Beta-carotene may lower vitamin E stores.

Beta-carotene supplements, reputed to stave off cancer and other diseases, may lower the body's supply of another presumed cancer fighter -- vitamin E -- scientists say.

Vitamin E and beta-carotene caught the attention of physicians because of their disease-preventing potential (SN: 9/18/93, p.183). Both substances can act as antioxidants, preventing the cell damage caused by carcinogens. Beta-carotene can also be converted in the body to vitamin A, which prevents night blindness.

Researchers had previously thought that the two substances did not interfere with each other in the body. "That had been the dogma for some time," says Thomas O. Frommel of Loyola University Medical Center in Maywood, Ill. But findings from new studies by Frommel and others suggest a different story.

For 3 months, Frommel and his colleagues gave 81 men and women who had been successfully treated for colon cancer or colon polyps daily doses of either 30 milligrams of beta-carotene or a placebo. They compared this group to 19 healthy volunteers who received no supplements.

Over the study period, concentrations of vitamin E in the colon tissue of the polyp-surgery patients who received beta-carotene decreased 52.6 percent, Frommel reports. Vitamin E in their blood remained stable; however, blood tests do not always indicate accurately the amount of vitamins available to body tissues.

Vitamin E concentrations in the colon tissue of recovered cancer patients who took beta-carotene didn't change significantly over the course of the experiment. But vitamin E concentrations in their blood did drop considerably, Frommel notes. Vitamin E stores in the tissue and blood of volunteers who received no beta-carotene remained unchanged. The researchers discussed some of these findings April 26 in Anaheim, Calif., at a Federation of American Societies for Experimental Biology conference.

David S. Alberts of the University of Arizona Health Sciences Center in Tucson and his colleagues gave either 30 mg of beta-carotene or 30 mg of beta-carotene plus 400 international units of vitamin E to 25 smokers and 25 nonsmokers for 9 months. After 6 months, those who took only beta-carotene showed a 25 percent drop in vitamin E concentrations in their blood. The scientists obtained similar results in earlier studies.

Blood samples from participants who received both supplements showed increased vitamin E. "The vitamin E supplement overcame the problem completely," asserts Alberts. The researchers are still analyzing the volunteers' tissue samples.

Not all researchers agree that beta-carotene diminishes vitamin E supplies. "In most of the large-scale clinical trials involving beta-carotene supplements there has not been a significant effect on plasma vitamin E," argues Robert S. Parker of Cornell University.

Studies may produce conflicting results because body weight, sex, age, and lipid concentrations in the blood of volunteers may all affect how beta-carotene and vitamin E interact, suggests Elaine B. Feldman of the Medical College of Georgia in Augusta.