Vitamin A, also called retinol, is a fat-soluble vitamin that is essential for humans. Adequate intake is important for normal vision and immune function. Dietary vitamin A can be provided as both preformed vitamin A and provitamin A carotenoids that are precursors to vitamin A. Preformed vitamin A is abundant in animal-derived foods like liver, kidney, eggs, and dairy products. Carotenoids, like beta-carotene, are found in darkly colored fruits and vegetables. Preformed vitamin A is efficiently absorbed through the intestines, while carotenoids may either be absorbed through the intestines intact or cleaved to form vitamin A prior to absorption. The proportion of beta-carotene converted to vitamin A decreases as beta-carotene intake increases, limiting the risk of vitamin A toxicity 1.
Dietary preformed vitamin A and provitamin A carotenoids have vitamin A activity that can be expressed as retinol activity equivalents (RAEs) or international units (IU). In the U.S., 1 RAE is equal to 3.33 IU vitamin A. The U.S. Food and Drug Administration (FDA) has established a Reference Daily Intake (RDI) of 5,000 IUs vitamin A for adults and children 4 or more years of age (21CFR101.9). RDIs are a set of dietary references for essential vitamins and minerals that are considered amounts sufficient to meet the daily requirements of healthy individuals. RDIs serve as the basis for calculating the percent daily value (%DV) amounts found on dietary supplement and food labels.