vitamin
n. an organic substance that in minute quantities is essential for normal growth and health. Many vitamins function as coenzymes, aiding in the metabolism of carbohydrates, fats, and proteins. A few vitamins can be synthesized in the human body, but most must be supplied in the diet. The most important are vitamin A, the vitamin B complex (including thiamine, riboflavin, pyridoxine, cyanocobalamin [B12], folic acid, nicotinic acid, and pantothenic acid), vitamin C (ascorbic acid), vitamin E, and vitamin K. Vitamins were so named in 1913 by Polish-born U.S. biochemist Casimir Funk (1884–1967), based on his belief that all vitamins were amines.