The human body requires vitamin A to operate properly, and like many vitamins it must be drawn from food-based sources. Animal-based foods such as liver supply vitamin A in ready-to-use form, while plant-based foods provide raw materials -- beta carotene and other carotenoids -- that your body uses to manufacture vitamin A. Vitamin A can be dangerous in excess, but beta carotene from dietary sources is essentially harmless. Beta carotene from supplements is more concentrated and can be problematic.
The Artificial Tan
If you eat a diet high in naturally occurring beta carotene from yellow vegetables such as carrots, sweet potatoes and winter squash or from green vegetables such as broccoli and chard, you might experience an odd result. High levels of beta carotene in your diet can give your skin a curiously orange tint, similar to the effect of an artificial-suntan product. It's not harmful, but unless you plan to impersonate a carrot or pumpkin at Halloween, it isn't especially desirable. The effect will subside if you reduce your consumption of beta carotene from food or supplements or both.
Cancer and Supplements
Several studies over the years have noted that people eating diets high in beta carotene showed lower incidence of some cancers, especially lung cancers. That doesn't hold true for people taking beta carotene supplements. In fact, the landmark 1996 Carotene and Retinol Efficacy Trial, or CARET -- intended to verify the effectiveness of supplements in preventing cancer -- found that current and former smokers taking beta carotene supplements actually showed an increased risk of contracting the disease.
Although dietary beta carotene is relatively innocuous, the concentrated form found in supplements can have undesirable interactions with specific medications. The University of Maryland Medical Center notes that beta carotene, taken in conjunction with vitamins E and C and the mineral selenium -- all found in multivitamins -- can reduce the effectiveness of some statins. It can also accelerate liver damage when combined with excessive alcohol consumption. Habitual drinkers, or those taking statins, should consult a physician before taking beta carotene supplements.
Doing the Math
Your total consumption of vitamin A and beta carotene, from dietary sources or supplements, should be keyed to recommended dietary allowances and kept below the acceptable upper limit, or UL. For adults, the RDA of preformed vitamin A is 3,000 international units and the UL is 10,000 IU. The RDA for vitamin A is equal to 6,000 IU of supplemental beta carotene and 18,000 IU of dietary beta carotene.
- Office of Dietary Supplements: Vitamin A
- Ask the Dietitian: Vitamin A and Carotenes
- Journal of the National Cancer Institute: Risk Factors for Lung Cancer and for Intervention Effects in CARET, the Beta-Carotene and Retinol Efficacy Trial
- University of Maryland Medical Center: Beta Carotene
- HealthAliciousNess: Top 10 Foods Highest in Beta Carotene
- National Institutes of Health: Dietary Supplement Label Database
- Linus Pauling Institute: Vitamin A
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