Several years ago

Cancer |

Several years ago, beta-carotene supplements were all the rage. Like vitamin E and C, beta carotene is a strong antioxidant, and animal studies have found that it can help prevent cancer. Furthermore, people who eat lots of food high in beta carotene (primarily yellow-orange and dark green vegetables) have been found to develop lung cancer and other forms of cancer less often.

However, studies designed to see whether beta-carotene supplements were helpful in people showed surprising results. Not only are beta-carotene supplements ineffective for this purpose, they might even increase the risk of cancer!

What Is Beta Carotene?

Beta carotene is a carotenoid. Carotenoids are one of the types of pigment that gives carrots and sweet potatoes their deep orange color. People obtain beta carotene by eating plant foods. Beta carotene consists of two vitamin A molecules attached to each other, which the body converts to usable vitamin A.

Beta Carotene’s Checkered History

In the early 1980s, a review of studies of the dietary habits of large groups of people found clear evidence that people who ate fruits and vegetables high in beta carotene had significant protection against several types of cancer, including lung cancer. In addition, beta carotene in supplement form seemed to lower cancer risk substantially in animals.

The idea that a simple nutritional supplement might prevent cancer was tremendously exciting. The National Cancer Institute eagerly funded intervention studies, where people taking beta-carotene supplements were compared to people taking placebo.

In 1994, the results of the first intervention trial—the Alpha-Tocopherol, Beta-Carotene (ATBC) study—came in. This study followed more than 29,000 male smokers who took supplements of either 50 mg of synthetic vitamin E, 20 mg of beta carotene, both, or placebo daily for 5 to 8 years. Apparently, taking beta carotene actually increased the risk of getting lung cancer by 18 percent.

The researchers thought these results were a fluke. But in January 1996, researchers monitoring another large study (aptly named CARET) confirmed the results: The group taking supplemental beta carotene had 28 percent more cases of lung cancer and 46 percent more lung-cancer deaths than those on placebo. Researchers canceled this study—which involved smokers and people exposed to asbestos—because the supplement appeared to increase death rates.

Later analysis found that the risk of beta-carotene supplements in this study might have been overstated. Probably the most we can say is that beta-carotene supplements do not seem helpful for preventing cancer.

What’s the Explanation?

The evidence suggests that a diet high in beta carotene shows clear-cut benefits against cancer, but a beta-carotene supplement apparently does not. Is this a contradiction? Not necessarily.

There is a difference between eating foods high in beta carotene and taking the nutrient in a pill. Foods that are high in beta carotene also contain large amounts of other healthy substances, such as other carotenes. Beta carotene might be a “marker” for a diet high in fruits and vegetables, and other substances in these plant foods might provide the cancer preventative effect.

Another possibility is that beta carotene might be protective only in the presence of other substances found in fruits and vegetables—the “teamwork” concept.

With conflicting evidence about supplements and cancer, you might wish to get this nutrient from your diet instead.

Food Sources of Beta Carotene

Here are a few foods with substantial amounts of beta carotene:
Sweet potato: 1/2 cup mashed, 1 baked, or 1 cup canned—16,000 to 28,000 IU
Carrot: 1 raw or 1/2 cup boiled slices—19,159 to 20,250 IU
Spinach: 1/2 cup canned, frozen, or boiled—7,300 to 9,400 IU
Mangoes, winter squash, papaya, cantaloupe, and greens are also rich in beta carotene.

Safety Issues

Beta carotene in multivitamin pills provides a safe source of vitamin A. High doses of vitamin A alone can cause liver problems as well as birth defects. Beta carotene does not. The worst effect you’re likely to notice with high doses of beta carotene is yellowish skin. Drinking lots of carrot juice can cause this too. Your skin will return to its natural color once you cut back on your intake.