VITAMINS are defined as carbon compounds that are needed in small amounts in the diet of animals. Amino acids, proteins, fats, carbohydrates, and minerals are excluded from this definition. Vitamins became known by the deficiency diseases that result from their absence. Such diseases have severe and distinctive signs and symptoms. The discovery, identification, and synthesis of the vitamins lessened the incidence of these diseases, including pellagra, rickets, scurvy, and others, so that they are now rare in the United States. The therapeutic effects of vitamins on deficiency diseases are so spectacular that popular attention has long been captivated by vitamins as components of the daily diet.
Foods that are good sources of vitamins often supply other important nutrients such as proteins and minerals. Many people are interested in warding off possible effects of partial or "subacute" vitamin deficiencies by selecting a good diet. Often, they also take pills containing synthetic