Beta-carotene is a chemical that occurs in nature as a coloring for various vegetables. Beta-carotene is an essential component of a healthy diet.
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Unfortunately, when beta-carotene is taken in large amounts as a dietary supplement, it can increase the occurrence of lung cancer among smokers and people exposed to asbestos.
In its natural form, beta-carotene is a member of the carotenoid family of chemicals, which gives some vegetables their orange, red or yellow colors, such as carrots.
When a carrot is eaten, the beta-carotene converts to vitamin A in the body. Vitamin A is critical to the human body's functioning.
Lack of vitamin A can cause children to go blind or die. Pregnant women deficient in vitamin A can develop night blindness, in which a person has serious trouble seeing at night or in badly-lit rooms. The World Health Organization (WHO) is conducting a campaign against vitamin A deficiency in areas of Africa and Southeast Asia, as described in a WHO article, "Vitamin A deficiency."
Scientists hoped to protect smokers from lung cancer by having them ingest daily beta-carotene supplements in large amounts. Beta-carotene in foods is known to be an antioxidant, a substance that protects cells from chemical damage.
Two studies, one in Finland and one in the United States, enrolled thousands of men and women who were smokers, former smokers and people exposed to asbestos through their jobs. Some study participants took large daily amounts of beta-carotene supplements; others were given placebo pills.
Unfortunately, both studies revealed that the participants taking large daily amounts of beta-carotene supplements had higher rates of lung cancer than participants taking placebo pills. A National Cancer Institute summary, "Beta-Carotene Supplements Confirmed as Harmful to Those at Risk for Lung Cancer," shows that the rate of lung cancer among Finnish study participants on beta-carotene supplements was 16 percent higher, and among American study participants the rate was 28 percent higher.
Another American study, in which nonsmokers were given daily beta carotene supplements, did not show any effect on the nonsmokers, either good or bad.
One theory about why beta-carotene supplements increased the cancer rate in these studies suggests that the cigarette smoke in smokers' lungs or exposure to asbestos creates a lung environment in which beta-carotene, as it breaks down, takes unusual forms that may assist cancer to develop.
Smokers, former smokers and people who have been exposed to asbestos should avoid taking large daily beta-carotene supplements.
A 2007 essay "Vitamin A," produced by the Linus Pauling Institute at Oregon State University, recommends that people should review any daily multivitamin pill that they are taking to make sure that it contains no more than 2,500 IU of Vitamin A.
If they are obtaining their Vitamin A through a supplement tablet or gel cap, it should contain no more than 5,000 IU of Vitamin A, and only 50 percent of that should come from beta-carotene.