Vitamins have been discovered over the last century as a result of the
investigations into what caused certain diseases. Vitamins are defined by two
essential characteristics. A vitamin must be a vital organic dietary substance
that is not carbohydrate, fat, or protein, and is necessary in very small
quantities to perform a metabolic function or prevent a deficiency state. A
vitamin cannot be manufactured by the body and therefore must be supplied by
food. The discovery of vitamin D has lead to the belief that it is more a
hormone than a vitamin, but still is discussed with vitamins.
There are two main classifications of vitamins according to their solubility in
solutions: fat-soluble and water-soluble. The fat-soluble vitamins are vitamin
A, vitamin E, vitamin D, and vitamin K. The presence of fat is required for the
assimilation of these vitamins in the body.
