Beta Carotene Won’t Reduce Cancer Risk, Studies Show

Two major federally funded studies have shown that taking supplements of beta carotene and vitamin A does nothing to prevent heart disease or lung cancer, and may even be harmful to smokers, researchers announced Thursday.

Scientists have long hoped to prove that beta carotene, which is found in fruits and vegetables and is converted by the body into vitamin A, can have a protective effect against the development of certain cancers--particularly lung cancer--as has been shown in animals.

But the researchers, their disappointment obvious, said that the years-long trials have shown no such benefit. And at least one study of smokers indicated that the supplements may increase the risk of cancer and death.

Americans, seeking easy routes to longer life and better health, have embraced the potential health benefits of dietary supplements with enthusiasm--and with their pocketbooks, turning it in recent years into a $4-billion-a-year industry.

But “beta carotene is no magic bullet,” said Dr. Richard Klausner, director of the National Cancer Institute.

One trial--which involved 18,314 participants, most of them current or former long-term smokers, and included 4,060 asbestos-exposed individuals--showed 28% more lung cancers and 17% more deaths in those taking beta carotene than those who took a placebo. The participants took 30 milligrams of beta carotene daily, and 25,000 international units of vitamin A.

Researchers said the results caused them to notify participants to stop taking the supplements.

The results of this trial support those of a controversial Finnish study released in 1994 that was widely criticized at the time as being flawed. That study involved 30,000 smokers in Finland, and found a similarly higher incidence of lung cancer and death in those taking the supplements.

The Finnish results surprised most researchers, who were expecting quite the opposite based on animal and other studies. Beta carotene and vitamin A are “antioxidants,” which are believed to prevent DNA damage caused by oxidant substances. Damage to DNA--which can come from both genetic and environmental factors--results in cancer. Animal and epidemiological studies have linked high dietary intake of beta carotene to a reduced risk of cancer, lung cancer in particular.

About one-fourth of the participants in the National Cancer Institute study were evaluated at the UC Irvine Medical Center’s Clinical Cancer Center. All of the 4,224 research subjects were smokers, clinic director Dr. Frank L. Meyskens said Thursday.

A second study, a 12-year trial involving 22,071 physicians, showed neither benefit or harm from taking the supplements. Most of the men in this study were nonsmokers. This is the same study population that in 1988 showed that low-dose aspirin reduces the risk of a first heart attack.

The Council for Responsible Nutrition, a trade group that represents the supplement industry, issued a statement Thursday saying that the studies “should not deter people from taking multivitamins containing recommended levels of nutrients, including beta carotene.”

Since “most people do not get recommended amounts of many nutrients, multivitamins help to fill nutrient gaps, and thus are beneficial to health,” the council added. Vitamin A and beta carotene “are desirable, necessary and safe components of multivitamins,” the group said.

Researchers emphasized that the studies were meant only to address the question of whether the supplements could reduce the risk of developing lung cancer, “and the simple answer is no,” Klausner said.

He said it was possible that beta carotene supplements could be dangerous for smokers. But he emphasized: “For individuals at risk for lung cancer due to tobacco smoking, there is a very clear message--the only way to reduce your risk is to stop smoking.”

Lung cancer is the leading cancer killer of both men and women in this country.

Scientists also said that the findings should not be used to dismiss the health benefits of a diet rich in fruits and vegetables. In diets, other factors associated with these foods likely are also at work, such as their high-fiber and low-fat content, and possibly other substances they contain.

“Many people would rather pop a pill than change their lifestyle,” but a beta carotene supplement “neither substitutes for a good diet nor compensates for a bad one,” said Dr. Charles Hennekens, principal investigator for the Physicians’ Health Study and chief of the division of preventive medicine at Brigham and Women’s Hospital in Boston.

“Taking a supplement of beta carotene is not equivalent to eating a diet that is rich in fruit and vegetables,” he added.

Dr. Gilbert S. Omenn, lead investigator for the smokers’ study, known as the Beta Carotene and Retinol Efficacy Trial, said he could not explain the results.

“Possibly the study was launched too late” or, because of the cumulative effects of smoking, “we were asking too much” of the supplements, said Omenn, who is also dean of the school of public health at the University of Washington in Seattle.

For the best protection against developing lung cancer, “stop smoking, do not smoke, and avoid cigarette smoke,” he advised.

Times staff writer H.G. Reza in Orange County contributed to this story.