Vitamins Do Not Cut Cancer Risk, 2 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 in high-risk individuals and may, in some cases, be harmful, researchers announced Thursday.
One of the studies, which included UCI Medical Center in Orange and five other research clinics in the United States, was terminated last week, 21 months early, when results indicated that the supplements might actually increase smokers’ risk of cancer. The study, which spanned four years, involved 4,224 local participants, all current or former smokers.
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 laboratory animals.
But the UCI researchers, their disappointment obvious, said the years-long trials have shown no such benefit.
Dr. Frank L. Meyskens, director of UCI Medical Center’s Clinical Cancer Center, who co-directed the local study, called the findings “puzzling and disturbing.”
“Beta carotene does not have a beneficial effect on individuals who smoke. [Instead] there appears to be a strong trend toward increased incidence of lung cancer in individuals who are smokers” and take large daily doses of beta carotene, Meyskens said.
Americans, always 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 them 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 in Bethesda, Md., which sponsored the two studies.
The trial that included UCI involved a total of 18,314 participants, most of them current or former long-term smokers, and included 4,060 asbestos-exposed individuals. It showed 28% more lung cancers and 17% more deaths among those taking beta carotene than among those who took a medically worthless placebo. The participants took 30 milligrams of beta carotene daily, and 25,000 international units (IU) of vitamin A.
The findings of this study were slightly different from those reached in a separate 12-year research program conducted by the Physicians’ Health Study, sponsored by Harvard University, that ended Dec. 31. Participants in the physicians’ study, which involved 22,071 male doctors, 51% of whom smoked at one time in their lives, who took 50 milligrams of beta carotene every other day.
Results of that study, also released Thursday, showed that participants were neither helped nor harmed by taking the supplements to combat heart disease and cancer. This is the same ongoing study population that in 1988 showed that regular low doses of aspirin reduce the risk of a first heart attack.
Researchers said the results of the UCI study caused them to notify participants to stop taking the vitamins. Meyskens said scientists do not know why beta carotene can aggravate lung cancer in smokers. However, he added that cancer experts have not ruled out the possibility that beta carotene can help fight other kinds of cancer.
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.
Although Meyskens would not go so far as to say that large doses of beta carotene can be toxic, he said the study involving the UCI Medical Center clinic showed that taking 30 milligrams daily--equivalent to eating five medium-size carrots--increased both the incidence of lung cancer in smokers and the chances of dying from cancer. He said the average daily beta carotene intake should be 3 milligrams.
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 factors and environmental assaults--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.
As for healthy nonsmokers who use beta carotene, Meyskens said, the study showed that the supplement was neither harmful or beneficial.
The National Nutritional Foods Assn., a Newport Beach-based trade group of companies that deal in natural health products and dietary supplements, attacked the studies as “misleading and politically motivated.”
Michael Q. Ford, executive director of the group, said in a written statement that it was “a ridiculous supposition” to even hypothesize that “beta carotene can reverse the ravages of cigarette smoking.”
“No one has ever suggested that beta carotene cures lung cancer,” said Ford, who defended the effectiveness of antioxidants such as beta carotene in preventing other diseases.
Researchers stressed 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 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 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.
Klausner agreed. “The studies do demonstrate how hard it is to isolate a single component of a healthful diet as the beneficial element,” he said. “Diet is extremely complex, involving hundreds of thousands of chemicals in combination. It’s what we eat and what we don’t eat. And often healthful diets are associated with a whole range of other healthful behaviors.”
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,” from the supplements, said Omenn, who is also dean of the School of Public Health at the University of Washington in Seattle.
He too emphasized that the best protection against developing lung cancer is to “stop smoking, do not smoke, and avoid cigarette smoke.”
