Conflicting Evidence: The Health Benefits of Beta-carotene

News Capsules: Three questionable studies cast doubt on the cancer-fighting benefits of beta-carotene

2-24-2011-2

Bright orange foods such as sweet potatoes and carrots are natural sources of potentially cancer-preventing beta-carotene.

Photo by Slice of Chic/ Courtesy Flickr: http://www.flickr.com/photos/sliceofchic/5347151255/sizes/m/

Content Tools

Beta-carotene

In 1996, the news media reported the results of three studies on beta-carotene, a nutrient purported to be rich in disease-fighting elements. But the news wasn’t good: the incidence of lung cancer among study volunteers actually increased while they were taking beta-carotene supplements.

Although scientists found flaws in the studies almost immediately, the bad news traveled quickly. A Forbes magazine article stated that all supplements may be a waste of money and that the Nobel Laureate and vitamin C researcher Linus Pauling might “still be alive today if not for those damn [vitamin C] pills.” (1) Pauling died at age ninety-three in 1994.

However, more than 200 studies have shown that beta-carotene can protect against cancer, stroke, and heart disease, as well as decrease cholesterol levels. So what’s the fuss about?

Three studies, three controversies

Beta-carotene is a pigment found in milk, some yellow and dark green vegetables such as broccoli, spinach, and carrots, and in fruits such as cantaloupes, peaches, and apricots. In the body, beta-carotene is converted into vitamin A, essential for normal eyesight, healthy tissue, strong immunity, and bone development.

Although the bulk of studies conducted on beta-carotene show that it does prevent disease, the three recent studies contradict those findings.

In the first study, known as the Physician’s Health Trial, 22,000 U.S. physicians took either 50 mg of beta-carotene or 325 mg of aspirin every other day for twelve years, ending in 1995. The results: No significant differences among the participants in incidence of cancer, heart disease, or overall mortality. Head researcher Charles H. Hennekens, M.D., of Harvard Medical School and Brigham and Women’s Hospital in Boston, stated in a National Cancer Institute press release that “beta-carotene supplementation is not a magic bullet—it can neither substitute for a good diet nor compensate for a bad one.”

The second study, the Beta-Carotene and Retinol Efficacy Trial, involved 18,000 U.S. volunteers aged fifty to sixty-nine who were smokers or former smokers or who had been extensively exposed to asbestos as determined by chest X-ray. Smokers and former smokers had smoked enough cigarettes to equal at least one pack a day for twenty years. From 1993 to 1996, half of the participants took 30 mg of beta-carotene plus 25,000 IU of vitamin A daily and the other half took a placebo. Those taking the beta-carotene and vitamin A had 28 percent more lung cancers and 17 percent more deaths than those taking the placebo, the study showed.

The third study, the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Trial, was conducted between 1986 and 1993. It involved 29,133 Finnish men aged fifty to sixty-nine who had smoked an average of a pack of cigarettes a day for thirty-six years. In the study they were randomly assigned to take one of the following daily for five to eight years: 50 mg of vitamin E, 20 mg of beta-carotene, both the vitamin E and beta-carotene, or a placebo. Those taking only vitamin E showed no increased incidence of lung cancer. How­ever, those taking only beta-carotene had 18 percent more lung cancers and 8 percent more lung-cancer deaths than those taking a placebo. The rate slightly increased for those volunteers who took beta-carotene and also consumed one or more alcoholic drinks a day. The men who took both ­vitamin E and beta-carotene showed no increase in the incidence of lung cancer.

A May 2, 1996, editorial in the New England Journal of Medicine stated that the studies should “put to rest any hopes that, for adults, beta-carotene supplements may be an effective means of lowering the risk of cancer and cardiovascular disease.”

On the other side

Other scientists, however, strongly disagreed. They cited six key concerns:

• The populations selected for the studies may have skewed the results.
• Beta-carotene works best with other antioxidants and is less effective in disease prevention when administered alone.
• Synthetic forms of beta-carotene, which were used in the studies, absorb and perform differently than natu­ral forms.
• The studies were too short to weed out cases of pre-existing lung cancer.
• Alcohol and smoking mutate beta-carotene when it is not administered with other nutrients. This mutation can damage cells and cause cancer.
• The studies were designed like drug studies, which measure the ­therapeutic effects on disease, not as a program of disease ­prevention, which is more ­appropriate for supplements.

Richard Passwater, Ph.D., director of research for Solgar Nutritional Research Center in Berlin, Maryland, who specializes in free-radical pathology, criticized the two studies as being flawed. In the Beta-Carotene and Retinol Efficacy Trial, for example, the difference in lung ­cancer death rates ­between those taking beta-carotene supplements and the placebo was equivalent to the difference between six and five cases of ­cancer per 100,000 people, which isn’t a statistically significant difference, Passwater said.

Moreover, the studies didn’t last long enough to identify lung cancers that may have been present in participants before they started the study, Passwater said. The studies involved participants who were at high risk for lung cancer and it is unreasonable, he said, to expect that taking beta-carotene for five years could reverse lung cancer in someone with a thirty-year history of smoking or a history of working with asbestos.

Most important, Passwater claimed, the studies ­ignored the fact that beta-carotene works with other ­nutrients to prevent illness. By not administering beta-carotene with nutrients that naturally protect it, such as selenium, the beta-carotene may have been mutated by contact with tobacco or alcohol in the blood and tissue of the subjects. The mutated beta-carotene could have caused cell damage leading to cancer, he said.(2)

In the February 1996 issue of The Nutrition Reporter, Jeffrey Blumberg, Ph.D., an antioxidant researcher and associate director of the U.S. Department of Agriculture’s Center for Human Nutrition and Aging at Tufts University, summed up his analysis of the beta-carotene controversy. “More than 200 scientific studies have shown that antioxidants, including beta-carotene, play a major role in preventing cancer and heart disease,” Blumberg wrote. “Well-controlled studies have also found beta-carotene to improve precancerous oral leukoplakia, common in smokers. Let’s not throw the baby out with the bathwater.”

References:

(1) Ross, Phillip E. “Spinach in a Pill.” Forbes November 4, 1996, 158, 11:354.
(2) Krinsky, N. I. “Antioxidant functions of carotenoids.” Free Radical Biology and Medicine 1989, 7:617–635.