Vitamins. Group of orange multivitamin pills on a white plastic spoon. Vitamins are complex organic substances required in small amounts for the normal functioning of the body; as well as for healthy growth and development. Most cannot be made in the body and so are essential components of a healthy diet. There are 13 vitamins A,C,D,E,K and the eight B group vitamins. A lack of sufficient quantities of any of the vitamins in the diet can lead to specific vitamin deficiency diseases.