Vitamins are compounds that you need in small amounts to remain
healthy and function normally. They help regulate the chemical
reactions the body undergoes to convert food into energy and for
tissue repair and regeneration. They're important for such
diverse functions as forming red blood cells to helping your
body fight and avoid infections. Vitamin doses are usually
measured in milligrams (MILL-uh-grams), micrograms, or
international units. Scientists group vitamins into two general
categories: those soluble (SAWL-you-bul) in fat and those
soluble in water. The fat-soluble vitamins, A, D, E, and K, are
stored in the body's fatty tissue and aren't regularly excreted
(eck-SKREE-ted) in the urine. The water-soluble vitamins,
Vitamin C and the B-complex vitamins, dissolve easily in water.
They're excreted in the urine, so they must frequently be
replaced. Vitamins and all other dietary supplements are
classified as 'foods' by the U-S Food and Drug Administration,
which regulates their safety and manufacturers'