What beta carotene is: Beta carotene, like some other carotenoids (natural plant pigments found in many deep yellow/ orange fruits and vegetables), can be converted by the body into vitamin A, as needed. It is an antioxidant.
Claims, purported benefits: Prevents cancer and heart disease; boosts immunity; supports good vision. It is an ingredient in many eye-health supplements, including those marketed to treat age-related macular degeneration.
What the studies show: Over the years, some good research—mostly involving beta carotene from food— has suggested that this vitamin-like substance may lower the risk of cancer and possibly other diseases. Thus, some nutrition experts have recommended beta carotene pills. But a decade ago two first-rate studies found that the supplements could increase the risk of lung cancer in smokers. A 2008 review published in the journal Cancer concluded that beta carotene supplements (20 to 30 milligrams a day, the amounts used in the studies) increase the risk of lung cancer in smokers by 24 percent. There’s no evidence implicating beta carotene from food.
Other studies have suggested that people who consume the most beta carotene (generally from food)— and possibly other carotenoids—have a reduced risk of heart disease and/or type 2 diabetes. But some studies found no such benefit. And a Danish meta-analysis in 2007 concluded that beta carotene supplements may, in fact, increase mortality rates slightly.
Side effects: Large amounts of beta carotene can turn your skin slightly yellow or orange, which is harmless. The supplements can be dangerous for smokers.
Bottom line: There is no daily recommended intake or safe upper level for beta carotene. Don’t assume that beta carotene in supplement form is beneficial or even harmless. Don’t take these pills, particularly if you’re a smoker. Most multivitamins contain low levels of beta carotene (about 1,000 IU, which is about 0.6 milligrams), an amount that is harmless. Still, no one knows what’s a safe dose for smokers.