tailieunhanh - Chapter 071. Vitamin and Trace Mineral Deficiency and Excess (Part 9)

Dietary Sources The retinol activity equivalent (RAE) is used to express the vitamin A value of food. One RAE is defined as 1 µg of retinol ( mmol), 12 µg of βcarotene, and 24 µg of other provitamin A carotenoids. In older literature, vitamin A was often expressed in international units (IU), with 1 RAE being equal to IU of retinol and 20 IU of β-carotene, but these units are no longer in current scientific use. Liver, fish, and eggs are excellent food sources for preformed vitamin A; vegetable sources of provitamin A carotenoids include dark green and deeply colored. | Chapter 071. Vitamin and Trace Mineral Deficiency and Excess Part 9 Dietary Sources The retinol activity equivalent RAE is used to express the vitamin A value of food. One RAE is defined as 1 gg of retinol mmol 12 gg of 0-carotene and 24 gg of other provitamin A carotenoids. In older literature vitamin A was often expressed in international units IU with 1 RAE being equal to IU of retinol and 20 IU of 0-carotene but these units are no longer in current scientific use. Liver fish and eggs are excellent food sources for preformed vitamin A vegetable sources of provitamin A carotenoids include dark green and deeply colored fruits and vegetables. Moderate cooking of vegetables enhances carotenoid release for uptake in the gut. Carotenoid absorption is also aided by some fat in a meal. Infants are particularly susceptible to vitamin A deficiency because neither breast nor cow s milk supplies enough vitamin A to prevent deficiency. In developing countries chronic dietary deficit is the main cause of vitamin A deficiency and is exacerbated by infection. In early childhood low vitamin A status results from inadequate intakes of animal food sources and edible oils both of which are expensive coupled with seasonal unavailability of vegetables and fruits and lack of marketed fortified food products. Concurrent zinc deficiency can interfere with the mobilization of vitamin A from liver stores. Alcohol interferes with the conversion of retinol to retinaldehyde in the eye by competing for alcohol retinol dehydrogenase. Drugs that interfere with the absorption of vitamin A include mineral oil neomycin and cholestyramine. Deficiency Vitamin A deficiency is endemic where diets are chronically poor especially in Southern Asia Sub-Saharan Africa some areas of Latin America and the Western Pacific including parts of China. Vitamin A status is usually assessed by measuring serum retinol normal range pmol L 30-100 pg dL or blood spot retinol or by tests of dark .