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' claims. Those sold in
supplement forms are labeled either 'natural' or 'synthetic.' Synthetic
vitamins are copies of the natural vitamins isolated from food. They're
usually cheaper in price, and their potency can be controlled. There's a
difference of opinion as to which is better, and whether or not the body
can tell the difference. The amounts of various vitamins that the body
needs daily used to be referred to as the 'recommended dietary
allowances,' or 'R-D-A's.' Today, they're classified by the percentage of
the daily value for each nutrient, or 'percent D-V.