Vitamins: What the Pharmacist Should Know
Wyandt, Christy M; Williamson, John S, Drug Topics
Most pharmacies today have a large inventory of vitamin supplements for sale, and the pharmacist is the key health-care professional available to provide information to the consumer about the appropriate use of these products. The primary purpose of this article is to provide sufficient information to the pharmacist about the traditional and emerging uses of vitamin supplements.
Vitamins and the diet The diet is the source of many nutrients that can be classifed as:
energy-yielding dietary components (carbohydrates, fats, and proteins);
sources of essential and nonessential amino acids (proteins); minerals; and
vitamins (water-soluble and lipid-soluble organic compounds)
Vitamins are a chemically diverse group of organic compounds that are needed to maintain health by regulating metabolism and assisting in the biochemistry of food digestion. Small quantities of each necessary vitamin must be provided exogenously, either because they cannot be synthesized in humans de novo or their rate of synthesis is too slow to produce sufficient quantities.
Most vitamins are provided through the diet, while vitamin D may be endogenously synthesized in the presence of ultraviolet light.
Vitamins are usually classified as water-soluble or lipidsoluble; their solubility influences their maintenance in the body. Water-soluble vitamins are stored in the body only to a limited extent, and frequent intake of these vitamins is needed to maintain adequate body levels. Lipid-soluble vitamins are maintained in the body much longer and therefore do not require frequent ingestion; however, they have a greater potential for toxicity.
Many vitamins become active only after transformation upon ingestion. For many water-soluble vitamins, activation results from phosphorylation and may require coupling to purine or pyrimidine nucleotides.
It is clearly understood that intake of the appropriate quantity of vitamins is essential for the maintenance of good health. The relationship between vitamins and various disease states is currently an important research topic, and it is important for the pharmacist to understand the role of vitamins in the treatment and prevention of disease and maintenance of good health.
In the United States, the National Academy of Science has a Food and Nutrition Board charged with recommending allowances of nutrients that will serve as a goal for good nutrition and will "encourage patterns of food consumption in the United States that will maintain and promote health." These allowances for water-soluble vitamins and for lipidsoluble vitamins are provided in Tables 1 and 2.
If the recommended level of vitamins is taken in, it is unlikely that a vitamin deficiency will occur. Although intake below the recommended daily allowance (RDA) does not necessarily indicate a deficiency, it is clear that the risk of vitamin deficiency increases in proportion to the extent to which the vitamin intake falls below the RDA.
Another consideration in making recommendations about vitamins is that they are generally reactive chemicals and therefore have the potential to interact negatively with pharmacologically active compounds. Table 3 provides a listing of several drug/nutrient interactions of which the pharmacist should be aware.
What follows is a detailed discussion about antioxidant vitamins as well as other water- and lipid-soluble vitamins. The antioxidant vitamins
The antioxidant vitamins are natural substances that may help prevent disease. Although the term antioxidant is widely used, it is seldom defined. For our purpose, an antioxidant will be defined as a substance that delays or inhibits oxidative damage to biological molecules.
All biological molecules are potential targets of oxidative damage. Although required for life, oxygen is toxic simply because it oxidizes organic molecules, including those composing human tissue. …