Studies have shown that a daily intake of around 30 mg of beta-carotene increases the risk of lung cancer and prostate cancer in smokers and people working in asbestos-related industries.
Beta-carotene is used in the food industry as a colorant additive E160a. The recommended daily intake of beta-carotene is 3 mg.
Following these studies, the American Cancer Society (ACS) and the UK-based charity Cancer Research UK called for warning labels on packages of dietary supplements containing beta-carotene, advising smokers about the increased risk of lung cancer associated with such supplements.
Beta-carotene is an antioxidant, and early research showed that people who consumed many foods rich in beta-carotene and other antioxidants had a lower risk of developing cancer.
However, two recent large-scale independent studies demonstrated that taking beta-carotene in tablet form actually increases the risk of lung cancer in smokers.
The first study, published in 1994 in "The New England Journal of Medicine", involved more than 29,000 male smokers in Finland. Half of the participants received beta-carotene, while the other half received a placebo. The group taking beta-carotene showed an 18% higher incidence of lung cancer.
The second study was conducted in the United States and was published in 1996 in the "Journal of the National Cancer Institute". It involved 18,000 male and female smokers. In the group taking a combination of beta-carotene and vitamin A, the incidence of lung cancer was 28% higher than in the group that did not take any supplements. Cancer-related mortality in this group was also 17% higher. Due to the clarity of these results and the health risks involved, the study had to be terminated early.
Later research helped explain why beta-carotene increases cancer risk in smokers. Beta-carotene enhances the activity of carcinogens in tobacco smoke, which cause damage to the body's DNA. Scientists know that DNA damage by carcinogens is often one of the first steps in turning a healthy cell into a cancerous one.
Manufacturers of dietary supplements containing natural beta-carotene argue that the studies used synthetic beta-carotene, and the results might have been different if natural sources of carotene had been used. There is a wide body of evidence suggesting that beta-carotene supplementation may have beneficial effects on the body.
