Beta carotene prove 'no magic bullet.' (National Cancer Institute research indicates that beta carotene provides no protection against heart disease or cancer)(Science News of the Week)(Brief Article)

The U.S. government has sobering news for devotees of beta carotene. The dietary supplement doesn't prevent heart disease or cancer, and it may even increase a smoker's risk of lung cancer.

Richard D. Klausner, director of the National Cancer Institute, part of the National Institutes of Health in Bethesda, Md., announced last Thursday that researchers conducting an NCI-funded study of 18,314 men and women at high risk of lung cancer stopped the study 21 months early. Interim results showed that participants who had been taking beta carotene and vitamin A for at least 4 years had a 28 percent increase in lung cancer and a 17 percent increase in deaths, compared to those taking a placebo.

"Beta carotene is no magic bullet-far from it," says Klausner. "The only way to reduce your risk is to stop smoking."

Klausner also announced that an NIH-funded study of 22,071 male physicians shows that beta carotene prevents neither heart disease nor cancer.

Beta carotene, from which the body makes vitamin A, is one of hundreds of carotenoids. These compounds are found in dark green and orange fruits and vegetables, such as carrots, peaches, and spinach. As an antioxidant, beta carotene prevents potentially cancer-causing DNA damage. Some studies indicate that people with diets high in beta carotene suffer less heart disease and lower cancer rates, particularly lung cancer (SN: 11/04/89, p. 294).

The Beta Carotene and Retinol Efficacy Trial (CARET) included 14,254 current and former smokers and 4,060 men exposed to asbestos. Every day, half of the participants took 30 milligrams of beta carotene and 7.5 times the recommended daily allowance of vitamin A; the other half took a placebo. The trial was stopped when an analysis mirrored results of a similar Finnish study of 30,000 male smokers. In that study, lung cancers increased by 18 percent and deaths by 8 percent among men taking 20 mg of beta carotene.

"We don't know why beta carotene has these adverse effects," says study leader Gilbert S. Omenn of the Fred Hutchinson Cancer Research Center in Seattle. "Beta carotene could also have a direct toxic effect."

Omenn noted that blood samples taken in the CARET study ruled out a speculation that beta carotene depletes stores of another antioxidant, vitamin E (SN: 5/14/94, p. 310).

Initially, the Finnish results were greeted with skepticism because hope for beta carotene was so high, says Klausner. He notes that CARET shows such hopes "cannot be presumed to be true, no matter how fervently held."

The Physicians' Health Study, headed by Charles H. Hennekens at Harvard Medical School in Boston, found the supplement conferred no benefit or harm on physicians, including smokers, who took 50 mg of beta carotene every other day for 12 years.

Beta carotene alone cannot prevent cancer or heart disease, Klausner notes. Other compounds, however, may confer the benefits found from eating a low-fat diet high in fruits and vegetables.

"In the U.S. today, many people would rather pop a pill than change their lifestyle," says Hennekens. "Beta carotene neither substitutes for a good diet nor compensates for a bad one."