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vitamin A
a fat-soluble vitamin that helps to maintain epithelial tissues that cover the body and line certain internal organs. It is
also essential for proper growth of skeletal and soft tissues, and is necessary for light-sensitive retinal pigments in the eye that make night vision possible. The particular manifestation of vitamin A deficiency depends upon the age of the patient. Among the most common
symptoms is night blindness. The skin may also be affected, becoming dry and pimply like a toad's skin. There are two forms of vitamin A: retinol (vitamin A1) and dehydroretinol (vitamin A2). It is manufactured by animals and humans from carotenes found in green leafy and yellow vegetables, including kale, broccoli, spinach, carrots, squash, and sweet potatoes. It is
obtained directly by eating animal products such as liver, eggs, whole milk, cream, and cheese. A toxic syndrome called hypervitaminosis A can result from excessive intake of this vitamin.
Copyright 2007. An Elsevier publication. All rights reserved.
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