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Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc
is increased with infection, and especially with fever (Alvarez et al., 1995; Stephensen et al., 1994). For these reasons, with parasitic infestation and during infection, the requirement for vitamin A may be greater than the requirements set in this report, which are based on generally healthy individuals.
Protein Energy Malnutrition. Protein synthesis generally, and specifically retinol binding protein synthesis, is reduced with severe protein energy malnutrition (PEM) (marasmus and kwashiorkor), and therefore release of retinol from the liver (assuming stores are present) is also reduced (Large et al., 1980). With successful dietary treatment of PEM, growth and tissue weight gain will be stimulated, and the relative requirement of vitamin A will increase during the recovery period.
Vegetarianism. Preformed vitamin A is found only in animal-derived food products. A clinical sign of vitamin A deficiency, night blindness, is prevalent in developing countries where animal and vitamin A-fortified products are not commonly available. Although carotenoids such as β-carotene are abundant in green leafy vegetables and certain fruits, because it takes 12 μg of dietary β-carotene to provide 1 retinol activity equivalent (RAE) (as compared to previous recommendations where 1 μg of retinol was thought to be provided by 6 μg of β-carotene [NRC, 1989 and Table 4-3]), a greater amount of fruits and vegetables than previously recommended are required to meet the daily vitamin A requirement for vegetarians and those whose primary source of vitamin A is green leafy vegetables.
Analyzing intakes of vitamin A and β-carotene and using an RAE of 12 μg for dietary β-carotene indicate that the RDA for vitamin A can be met by those consuming a strict vegetarian diet containing the deeply colored fruits and vegetables (1,262 μg RAE) that are major sources of β-carotene in the United States (Chug-Ahuja et al., 1993) (Table 4-6). The United States has several vitamin A-fortified foods, including milk, cereals, and infant formula. Furthermore, certain food products, such as sugar, are being fortified with vitamin A in some developing countries. If menus are restricted in the amounts of provitamin A carotenoids consumed and such fortified products are not part of routine diets, then vitamin A supplements may be required.
Populations Where Consumption of Vitamin A-Rich Foods is Limited. Three major intervention trials have been conducted in developing countries to evaluate the efficacy of provitamin A carotenoids in