Vitamin A

Vitamin A is retinol. Carotene compounds (found, for example, in egg yolk, butter and cream) are gradually converted by the body to vitamin A (retinol). A form of vitamin A called retinal is responsible for transmitting light sensation in the retina of the eye. Deficiency of vitamin A leads to night blindness. The word "vitamin" was coined in 1911 by the Warsaw-born biochemist Casimir Funk (1884-1967). At the Lister Institute in London, Funk isolated a substance that prevented nerve inflammation (neuritis) in chickens raised on a diet deficient in that substance. He named the substance "vitamine" because he believed it was necessary to life and it was a chemical amine. The "e" at the end was later removed when it was recognized that vitamins need not be amines. The letters (A, B, C and so on) were assigned to the vitamins in the order of their discovery. The one exception was vitamin K which was assigned its "K" from "Koagulation" by the Danish researcher Henrik Dam. The vitamins include: {{}}Beta carotene: An antioxidant which protects cells against oxidation damage that can lead to cancer. Beta carotene is converted, as needed, to vitamin A. Food sources of beta carotene include vegetables such as carrots, sweet potatoes, spinach and other leafy green vegetables; and fruit such as cantaloupes and apricots. Excessive carotene in the diet can temporarily yellow the skin, a condition called carotenemia, commonly seen in infants fed largely mushed carrots. Vitamin B1: Thiamin, acts as a coenzyme in body metabolism. Deficiency leads to beriberi, a disease of the heart and nervous system. Vitamin B2: Riboflavin, essential for the reactions of coenzymes. Deficiency causes inflammation of the lining of the mouth and skin. Vitamin B3: Niacin, an essential part of coenzymes of body metabolism. Deficiency causes inflammation of the skin, vagina, rectum and mouth, as well as mental slowing. Vitamin B6: Pyridoxine, a cofactor for enzymes. Deficiency leads to inflammation of the skin and mouth, nausea, vomiting, dizziness , weakness and anemia. Folate (folic acid): Folic acid is an important factor in nucleic acid synthesis (the genetic material). Folate deficiency leads to megaloblastic anemia. Vitamin B12: An essential factor in nucleic acid synthesis (the genetic material of all cells). Deficiency leads to megaloblastic anemia, as can be seen in pernicious anemia. Vitamin C: Ascorbic acid, important in the synthesis of collagen, the framework protein for tissues of the body. Deficiency leads to scurvy, characterized by fragile capillaries, poor wound healing, and bone deformity in children. Vitamin D: A steroid vitamin which promotes absorption and metabolism of calcium and phosphorus. Under normal conditions of sunlight exposure, no dietary supplementation is necessary because sunlight promotes adequate vitamin D synthesis in the skin. Deficiency can lead to osteomalcia in adults and bone deformity (rickets) in children. Vitamin E: Deficiency can lead to anemia. Vitamin K: An essential factor in the formation of blood clotting factors. Deficiency can lead to abnormal bleeding.

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vitamin A n any of several fat-soluble vitamins or a mixture of two or more of them whose lack in the animal body causes keratinization of epithelial tissues (as in the eye with resulting night blindness and xerophthalmia): as

a) a pale yellow crystalline highly unsaturated alicyclic alcohol C₂₀H₂₉OH that is found in animal products (as egg yolk, milk, and butter) and esp. in marine fish-liver oils (as of cod, halibut, and shark) and that is used in various forms in medicine and nutrition called also retinol, vitamin A₁

b) a yellow viscous liquid alicyclic alcohol C₂₀H₂₇OH that contains one more double bond in a molecule than vitamin A₁ and is less active biologically in mammals and that occurs esp. in the liver oil of freshwater fish called also vitamin A₂

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a fat-soluble vitamin that occurs preformed in foods of animal origin (especially milk products, egg yolk, and liver) and is formed in the body from the pigment b-carotene, present in some vegetable foods (for example cabbage, lettuce, and carrots). Retinol is essential for growth, vision in dim light, and the maintenance of soft mucous tissue. A deficiency causes stunted growth, night blindness, xerophthalmia, keratomalacia, and eventual blindness. The recommended daily intake is 750 µg retinol equivalents for an adult (1 µg retinol equivalent = 1 µg retinol or 6 µg b-carotene).

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1. retinol or any of several related fat-soluble compounds having similar biological activity; the vitamin acts in numerous capacities, particularly in the functioning of the retina, the growth and differentiation of epithelial tissue, the growth of bone, reproduction, and the immune response. Deficiency of vitamin A causes skin disorders such as xeroderma and follicular hyperkeratosis, increased susceptibility to infection, nyctalopia, xerophthalmia, and other eye disorders, anorexia, and sterility. As vitamin A, it is mostly found in liver, particularly of fish, egg yolks, and the fat component of dairy products; its other major dietary source is the provitamin A carotenoids of plants. 2. a preparation of retinol or esters of retinol formed from edible fatty acids, usually acetic and palmitic acids, used in the prophylaxis and treatment of vitamin A deficiency. Vitamin A is toxic when taken in excess; see hypervitaminosis A. The term vitamin A is sometimes used to refer specifically to retinol.