Vitamins are certain chemicals the body needs in small amounts to function properly. They work in a variety of ways, mostly as "helpers;" for example, many of the B vitamins help the body use protein, fats, and carbohydrates.

Vitamins are divided into two categories:

• Water-soluble vitamins include all the B vitamins and vitamin C. Water-soluble vitamins travel freely through the body, and the part that the body doesn't use passes through the kidneys and leaves the body as urine or stool. The body needs water-soluble vitamins in frequent, small doses, and they are unlikely to reach toxic levels.
• Fat-soluble vitamins include vitamins A, D, E, and K. Fat-soluble vitamins are stored in the body's cells and are not passed out of the body as easily as water-soluble vitamins. They do not need to be taken in as frequently as water-soluble vitamins (although adequate amounts are needed), and they are more likely to reach toxic levels if a person takes in too much.