ABSTRACT
Vitamins are organic compounds that are essential in the diet in small amounts for the purpose of promoting and regulating body functions necessary for growth, reproduction,
Overview 56 ❚
Fat-soluble vitamins 60 ❚
Water-soluble vitamins 70 ❚
Summary 80 ❚
synthesized in the body or because their synthesis can be decreased by environmental factors. Notable exceptions to having a strict dietary need for a vitamin are vitamin A, which we can synthesize from certain pigments in plants, vitamin D, synthesized in the body if the skin is exposed to adequate sunlight, niacin, synthesized from the amino acid tryptophan, and vitamin K and biotin, synthesized to some extent by bacteria in the intestinal tract. To qualify as a vitamin, a compound must meet the following two criteria of an essential nutrient: (1) the body is unable to synthesize enough of the compound to maintain health; and (2) absence of the compound from the diet for a certain period produces deficiency symptoms that, if caught in time, are quickly cured when the substance is resupplied. A substance does not qualify as a vitamin merely because the body cannot synthesize it. Evidence must suggest that health declines when the substance is not consumed. Vitamins differ from carbohydrates, lipids, and proteins in the following ways:
• Structure – vitamins are individual units; they are not linked together as are the molecules glucose, fatty acids, and amino acids.
