Any of various chemically unrelated organic compounds that are necessary in small quantities for the normal functioning of the human body. Many act as coenzymes, small molecules that enable enzymes to function effectively. Vitamins must be supplied by the diet because the body cannot make them. They are normally present in adequate amounts in a balanced diet. Deficiency of a vitamin may lead to a metabolic disorder (“deficiency disease”), which can be remedied by sufficient intake of the vitamin. They are generally classified as water-soluble (B and C) or fat-soluble (A, D, E, and K). See separate entries for individual vitamins, also nicotinic acid, folic acid, and pantothenic acid.
Scurvy (the result of vitamin C deficiency) was observed at least 3,500 years ago, and sailors from the 1600s were given fresh sprouting cereals or citrus fruit juice to prevent or cure it. The concept of scurvy as a deficiency disease, however, caused by the absence of a specific substance, emerged later. In the 1890s a Dutch doctor, Christiaan Eijkman, discovered that he could cure hens suffering from a condition like beriberi by feeding them on whole-grain, rather than polished, rice. In 1912 Casimir Funk, a Polish-born biochemist, had proposed the existence of what he called “vitamines” (vital amines), but it was not fully established until about 1915 that several deficiency diseases were preventable and curable by extracts from certain foods. By then it was known that two groups of factors were involved, one being water-soluble and present, for example, in yeast, rice-polishings, and wheat germ, and the other being fat-soluble and present in egg yolk, butter, and fish-liver oils. The water-soluble substa
nce, known to be effective against beriberi, was named vitamin B. The fat-soluble vitamin complex was at first called vitamin A. As a result of analytical techniques these have been subsequently separated into their various components, and others have been discovered.
Any of a group of organic substances essential in small quantities to normal metabolism; SYN. vitamine.