Many people take daily multivitamins to improve and maintain good health. Vitamin A, found in many dietary supplements, is known to support eye function, tissue growth, as well as bone, reproductive, and immune function.
What many people do not know is Vitamin A comes in many forms. The two main forms consumed by humans are retinol, found in animal sources of food, and beta carotene, an orange plant form. These forms are both metabolized by the body to the active form of vitamin A, retinoic acid.
Many people are also not aware that the recommended daily allowance (RDA) for vitamin A differs according to the form consumed. Food labels list vitamin A in International Units (IUs,) and the RDA use RAE, or Retinol Activity Equivalents for each type of Vitamin A available. For instance, it takes different IU amounts of beta-carotene from food and from dietary supplements to make 1 microgram of retinoic acid, the biologically active form of Vitamin A. So when examining the amount of vitamin A consumed in relation to one’s RDA, it is important to consider where the vitamin A comes from and in what form.
The recommended dietary allowance of vitamin A for an average adult (14 years +) is 700 micrograms RAE (2,300 IUs of retinol, or 4,600 IUs beta carotene from supplements) for females and 900 mircograms RAE (3,000 IUs of retinol, or 6,000 IUs of beta carotene from supplements) for males. Children require even less vitamin A, between 300 and 600 RAE depending on age (1,000- 2,000 IUs retinol, 2,000-4,000 IUs beta carotene from supplements.) Dietary supplements usually supply vitamin A in a combination of the forms of beta-carotene and preformed vitamin A, or retinol. Multivitamin supplements typically contain 2,500 to 10,000 IUs of Vitamin A.
One A Day’s Women’s multivitamin, for instance, contains 4,000 IUs of Vitamin A, with 50 % in the form of beta-carotene. 2,000 IUs of beta-carotene from a dietary supplement, once metabolized to retinoic acid, is equal to 300 RAE of Vitamin A. The remaining 2,000 IUs are found in the form of Vitamin A acetate, a preformed form equal to 600 RAE. So this vitamin totals 900 RAE of vitamin A, exceeding the RDA for women, 700, by 200 micrograms. A person also consumes various amounts of vitamin A in a typical diet, further exceeding the RDA. A ¬Ω cup of carrots contains around 450 micrograms RAE (9,000 IUs beta carotene from food) for instance, which is about half or more than your daily need.
The tolerable upper limit (UL) of Vitamin A for adults is 3,000 micrograms RAE, (10,000 IUs retinol, 20,000 IUs of beta carotene from supplements, or 60,000 IUs beta carotene from food) which will not typically be exceeded by common multivitamins. The UL for children can be as low as 600 micrograms RAE (2,000 IUs retinol, 4,000 IUs beta carotene from supplements.) However, Vitamin A is a fat-soluble vitamin, meaning excess amounts consumed are stored in the body, often in the liver. Hypervitaminosis A or Vitamin A toxicity, is more likely to occur when taking supplements containing preformed vitamin A and beta-carotene than when only consuming vitamin A from the diet. Chronic excessive intake of Vitamin A is associated with dizziness, nausea, skin irritation, joint pain, and, according to some studies, increased risk of lung cancer and cardiovascular disease. Excessive intake of preformed vitamin A is a known teratogen, meaning it can cause birth defects like malformations of the eye, skull, lung and heart.
THE BOTTOM LINE
A diet with variety in fruits and vegetables will typically fulfill an individual’s vitamin A need. Special consideration should be taken when choosing multivitamins with vitamin A, especially for children. When considering supplements, it is wise to reference established values for vitamins and minerals on government (.gov) website databases like the National Institute of Health: Office of Dietary Supplements.
National Institute of Health. "Dietary Supplement Fact Sheet: Vitamin A." Office of Dietary
Supplements. Office of Dietary Supplements, 25 July 2012. Web. 26 Mar. 2013.
"One a Day Women's: Overview." One a Day. N.p., 2012. Web. 26 Mar. 2013. <http://oneaday.com/
UConn Extension Nutrition Intern