NUTRITION HOTLINE
By Reed Mangels, PhD, RD
QUESTION: If I eat a lot of carrots and sweet potatoes, do I have to worry about vitamin A toxicity?
CL, via e-mail
ANSWER: The short answer is, "No, you won't develop a vitamin A toxicity from eating a lot of carrots and sweet potatoes."
There are two forms of vitamin A in food. The first, called preformed vitamin A retinol, or retinyl ester, is found in foods from animal sources including dairy products, fish, and meat. This form of vitamin A would only be found in a vegan diet in supplements and fortified foods. Preformed vitamin A can be chemically synthesized.1
The second form of vitamin A comes from provitamin A carotenoids. These substances, which our body uses to make vitamin A, are found in plants, especially dark orange or yellow vegetables and fruits, leafy green vegetables, and tomatoes. The most important provitamin A carotenoid is beta-carotene. The two other provitamin A carotenoids are alpha-carotene and beta-cryptoxanthin. Even large amounts of the provitamin A carotenoids over a long period of time aren't associated with vitamin A toxicity.2 Some studies suggest that when blood vitamin A concentrations are high, a lower amount of provitamin A carotenoids are absorbed or converted to vitamin A. If you eat large amounts of food like carrots and sweet potatoes regularly, you may notice your skin has an orangish tint, which is especially visible on the soles of the feet and palms of the hands. This condition, called carotenodermia, is harmless and goes away when carotenoid intake is reduced.
In contrast, excess amounts of preformed vitamin A, either as a single massively large dose, or intakes consistently above what is considered a safe upper level, can cause vitamin A toxicity. Toxicity is usually reported following overuse of supplements containing preformed vitamin A, although there is at least one account of vitamin A toxicity after eating polar bear liver,3 which is very high in preformed vitamin A. Symptoms of vitamin A toxicity include dizziness, nausea, headaches, and joint and bone pain; vitamin A toxicity can be fatal. Some studies have found that high intakes of preformed vitamin A are associated with reduced bone density and increased fracture risk. Excess intakes of preformed vitamin A, typically from supplements, during pregnancy, can cause congenital birth defects. The Tolerable Upper Limit Level for preformed vitamin A is 3000 micrograms Retinol Activity Equivalents (10,000 IU) for adults including pregnant women. Provitamin A carotenoids from plants are a good way to get vitamin A without having to be concerned about toxicity. In addition, you'll get other benefits from fruits and vegetables, including fiber and vitamin C.
REFERENCES
1 Yacoubou, J. Vegetarian Journal's Guide to Food Ingredients. www.vrg.org/ingredients/index.php#vitamin_a. Partially updated 2010.
2 Grune T, Lietz G, et al. Beta-carotene is an important vitamin A source for humans. J Nutr. 2010;140:2268S-85S.
3 Rodahl K, Moore T. The vitamin A content and toxicity of bear and seal liver. Biochem J. 1943-37:166-8.
