vitamin A also called retinol Fat-soluble alcohol, most abundant in fatty fish and especially in fish-liver oils. It is not found in plants, but many vegetables and fruits contain beta-carotene (see carotene), which is readily converted in the body to vitamin A. It functions directly in vision, especially night vision. A derivative, retinaldehyde, is a component of the visual pigments, including rhodopsin, in the retina. Humans require vitamin A in very small amounts. Unlike carotenes, it is toxic in large amounts and is readily destroyed by exposure to heat, light, or air.
vitamin B complex Water-soluble organic compounds with loosely similar properties, distribution in natural sources, and physiological func¬ tions. Most are coenzymes, and all appear essential to the metabolic pro¬ cesses of all animal life. They include thiamin (B x ), riboflavin (B 2 ), niacin, vitamin B 6 , pantothenic acid, fouc acid, biotin, and vitamin B 12 (cobal- amin); some authorities also include choline, carnitine, lipoic acid, inos¬ itol, and para-aminobenzoic acid. Vitamin B 6 is needed for metabolism of amino acids and prevention of skin and nerve disorders. Vitamin B 12 prevents pernicious anemia and is involved in nucleic-acid synthesis, fat metabolism, and conversion of carbohydrate to fat. The B complex vita¬ mins are particularly abundant in cereal grains, meats, nuts, and some fruits and vegetables.
vitamin C or ascorbic acid Water-soluble organic compound impor¬ tant in animal metabolism. Most animals produce it in their bodies, but humans, other primates, and guinea pigs need it in the diet to prevent scurvy. It is essential in collagen synthesis, wound healing, blood-vessel maintenance, and immunity. Some studies have found a moderate benefit of vitamin C in reducing the duration and severity of the common cold. It works as an antioxidant in the body and is used as a preservative. It is easily destroyed by oxygen. Excellent sources are citrus fruits and fresh vegetables.
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2012 I vitamin D ► Vivekananda
vitamin D Any of a group of fat-soluble alcohols important in calcium metabolism in animals to form strong bones and teeth and prevent rickets and osteoporosis. It is formed by ultraviolet radiation (sunlight) of sterols (see steroid) present in the skin. The most important of these sterols are 7-dehydrocholesterol, formed by metabolic processes in animals, and ergosterol, present in vegetable oils. The action of sunlight on the skin con¬ verts these two compounds, respectively, to cholecalciferol (vitamin D 3 ) and ergocalciferol (vitamin D 2 ). Vitamin D is added to margarine, milk, and cereals for the benefit of those who may not get enough sunlight in winter. As little as 5 micrograms each day appeal - adequate for children. Because the body cannot excrete it, prolonged high intake can cause a toxic reaction including fatigue, nausea, and abnormal calcium accumulation.
vitamin E or tocopherol Vto-'ka-fo-.rolX Fat-soluble organic com¬ pound found principally in certain plant oils and leaves of green veg¬ etables. Vitamin E acts as an antioxidant in body tissues and may prolong life by slowing oxidative destruction of membranes. Certain rodents require it for normal reproduction. Besides uses in foods and in nutritional research and supplements, it is used to retard rancidity in fats, especially vegetable oils.
vitamin K Any of several fat-soluble compounds essential for the clot¬ ting of blood. A deficiency of vitamin K in the body leads to an increase in clotting time. In 1929 a previously unrecognized fat-soluble substance present in green leafy vegetables was found to be required for coagula¬ tion of the blood; its letter name comes from the Danish word koagula- tion. A pure form was isolated and analyzed structurally in 1939; several related compounds having vitamin-K activity have since been isolated and synthesized. The form of vitamin K that is important in mammalian tis¬ sue is of microbial origin. A synthetic vitamin K precursor called mena¬ dione is used as a vitamin supplement.
Vitellius \vi-'tel-e-3s\, Aulus (b. ad 15—d. Dec. 20, 69, Rome) Roman emperor (69), the last of Nero’s three short-lived successors. Vitellius was commander of the Lower German army when Nero died and was pro¬ claimed emperor by his troops. When he marched on Italy, Otho, a rival emperor, committed suicide. Vitellius entered Rome but there had to con¬ tend with Vespasian, whose army had also proclaimed him emperor; the troops of Vitellius lost to those of Vespasian. Vitellius’s Praetorian Guard prevented him from abdicating, but he was captured by troops, dragged through the streets, tortured, and killed.
Viti Levu \'ve-te-'la-vu\ Island (pop., including adjacent islands, 1996: 594,791), Fiji, South Pacific Ocean. The country’s largest island, it has an area of 4,011 sq mi (10,388 sq km). Suva, the Fijian capital, is situ¬ ated on the island’s southeastern coast. It was sighted by Capt. William Bligh in 1789. A central mountain range divides the island into wet and dry sections. Mount Tomanivi, the highest point in Fiji, rises 4,341 ft (1,323 m). Islanders grow sugar, pineapples, cotton, rice, and tobacco. There is a goldfield in the north-central part of the island.
vitiligo \,vit- 3 l-'I-go\ or leukoderma Skin disorder manifested by smooth, white spots on various parts of the body. Though the pigment¬ making cells of the skin, or melanocytes, are structurally intact, they have lost the ability to synthesize the pigment. The reason for the condition is unclear. Individuals with vitiligo (about 1% of the adult population) are usually in good general health, but vitiligo presents a cosmetic problem that can be serious in dark-skinned individuals. Normal skin color rarely returns, and there is no known cure.
Vitoria \ve-'tor-y3\ City (pop., 2002 est.: 299,400), eastern Brazil. Located on the western side of Vitoria island in Espfrito Santo Bay, it was founded by the Portuguese in 1535 and was made a provincial capital in 1823. It was Brazil’s leading port for exporting iron ore until the 1960s. Its economy is based now on textile factories, sugar refineries, and other small manufacturing plants as well as on the shipment of coffee.
Vitoria \ve-'tor-e-3\ -Gasteiz City (pop., 2001: 216,852), capital of Basque Country autonomous community, northeastern Spain. The official name derives from the combined Spanish (Vitoria) and Basque (Gasteiz) names for the city. Founded as Victoriacum by the Visigothic king Leovig- ild in 581, it was granted a charter in the 12th century. In 1200 Alfonso VIII captured it and incorporated it into his kingdom. In 1813 it was the scene of a battle in which allied forces under English Gen. Arthur Welle¬ sley (later duke of Wellington) defeated the French, driving them from Spain and leading to the end of the Peninsular War. Now a manufactur¬ ing centre, it retains several medieval buildings.
vitriol, oil of See sulfuric acid
Vitruvius \v3-'tru-ve-3s\ in full Marcus Vitruvius Pollio (fl. 1st century bc) Roman architect, engineer, and author of the celebrated trea¬ tise De architectural a handbook for Roman architects. Little is known of his life except what can be gathered from his writings. The treatise is divided into 10 books covering almost every aspect of architecture and city planning. His wish was to preserve the Classical Greek tradition in the design of temples and public buildings, and his prefaces contain many pessimistic remarks about the architecture of the time. His work was the chief authority on ancient Classical architecture throughout the antique revival of the Renaissance, the Classical phase of the Baroque, and the Neoclassical period.