Vitamin, specific nutrient compounds essential for body growth or metabolism and which can be supplied by a balanced diet or, when necessary, in the form of supplements. Enzymes and coenzymes are necessary for metabolism, especially the processes by which the body absorbs and utilizes nutrients. But there are certain coenzymes the body can obtain only from vitamins. Vitamins are denoted by letters and are often divided into fat-soluble and water-soluble kinds. Fat-soluble vitamins can be stored in the body's fat; water-soluble vitamins pass out of the body through urine. The A, D, E, and K vitamins are fat soluble; the B and C vitamins are water soluble.
Vitamin A, or retinol, is essential for skeletal growth, healthy epithelial tissue, and eyesight. It is found in milk, butter, and egg yolks. Green leafy or yellow vegetables contain a substance called carotene, which the body converts to Vitamin A. Vitamin A deficiency can cause skin, eye, or mucous membrane lesions. Overdoses can be harmful to the skin. Vitamin D, or calciferol, is a crucial factor in calcium metabolism, especially the growth and maintenance of bone. It is found in human skin and is activated with exposure of the skin to sunlight. Vitamin D deficiency can cause rickets or bow legs. An overdose can cause kidney damage. Vitamin E, or tocopherol, appears to play a role in blood cell and nervous system tissues, but its precise functions and properties have yet to be determined. It is found in peanuts, vegetable oils, wheat germ, and green leafy vegetables. Vitamin K provides essential cofactors for the production of certain clotting factors in the liver. It is used to treat some clotting disorders. Vitamin K is contained in liver and green leafy vegetables.
Important members of the B group include B1 or thiamine; B2 or riboflavin; niacin; B6 or pyridoxine; folic acid; and B12 or cyanocobalamin. Thiamine acts as a coenzyme in carbohydrate metabolism. It occurs naturally in whole grains, yeast, nuts, and lean pork. Its deficiency, seen in rice-eating populations and alcoholics, causes beriberi. Riboflavin is also a coenzyme active in oxidation reactions. It is found in milk, green leafy vegetables, and liver and organs. A deficiency will cause lesions of the skin, mouth, or eyes. Niacin is a general term for nicotinic acid and nicotinamide, coenzymes in carbohydrate metabolism. Niacin occurs in wheat germ, lean meat, fish, and peanuts. A deficiency causes pellagra and, if the deficiency is extreme, it can cause death. Pyridoxine provides an enzyme important in energy storage and its deficiency can lead to anemia. It occurs naturally in lean meat, whole grains, milk, and egg yolks. Folic acid is an essential cofactor in the metabolism of nucleic acid and a deficiency of the vitamin, which is not uncommon in pregnancy, can cause anemia. Folic acid occurs naturally in yeast and in green leafy vegetables. Cyanocobalamin is essential for all the body's cells and a deficiency can lead to pernicious anemia. It occurs naturally in bivalves and fish, eggs and lean meat, and rigorous vegetarians are at particular risk of deficiency. Pantothenic acid, biotin, choline, inositol, and para-aminobenzoic acid are other members of the B-group. Vitamin C, another of the water-soluble vitamins, is also known as ascorbic acid and plays an important role in the healing process, blood cell formation, and bone and tissue growth. It occurs naturally in citrus fruits, cabbage, berries, peppers, and tomatoes. Deficiency leads to scurvy, and extreme and prolonged deficiency causes death. The beneficial effects of Vitamin C in the prevention and treatment of the common cold have yet to be conclusively determined.