Vitamins are molecules that are essential for normal body functioning. They make possible the processes in the body that digest, absorb, and use nutrients. There are 15 vitamins, most of which cannot be made by the body and must be supplied in the diet. Vitamins are needed in very small amounts by the body, but when they are not provided, deficiency diseases may occur. These diseases are relatively rare in Western countries, but some are still common in less wealthy parts of the world. The vitamins can be divided into two groups. Vitamins A, D, E, and K are fat-soluble vitamins. Vitamin C...ascorbic acid, and the B-group vitamins, B1...thiamine, B2... riboflavin, B3...niacin, B6, B12, folacin, pantothenic acid and biotin, are water-soluble.