HEALTH AND MEDICAL PRODUCTS:VITAMINS.

VITAMINS

Within complex biological organisms, nutrients such as proteins, carbohydrates, and fats serve as building blocks and combine with various other substances to yield energy and maintain cellular functioning. These chemical reactions are catalyzed (accelerated) by individual enzymes, which are located in specific body regions. Vitamins are potent organic (carbon- based) compounds that mainly function as coenzymes (or parts of coenzymes) that individually act in concert with each enzyme to accomplish a specific type of reaction catalysis process. Vitamins are classified as either fat-soluble or water-soluble. Fat-soluble vitamins (e.g., A, D, E, and K) bind to ingested fats and are absorbed into the body along with their digestive products. Except for vitamin K, fat-soluble vitamins are generally stored within the body. Water-soluble vitamins (e.g., B complex and C) are absorbed along with water from the gastrointestinal tract, and unless metabolically used, they are usually excreted in the urine. A noted exception regarding absorption is water-soluble vitamin B12, which must first bind to a chemical called intrinsic factor, which is produced by the stomach, to be absorbed into the body.

These essential organic compounds are biologically required only in small amounts, but deficiency tends to result in a diseased state for the individual. With a few noted exceptions (e.g., vitamins D, K, and B3), most vitamins are not manufactured within the body and thus must be obtained via food sources or direct vitamin supplementation. The value of certain foods in maintaining health was recognized long before the first vitamins were actually isolated and characterized. Nearly 3,500 years ago, for example, Egyptians recognized that night blindness (caused by vitamin A deficiency) could be treated with specific foods. In the eighteenth century, it was demonstrated that the addition of citrus fruits to the diet could prevent the development of scurvy (caused by vitamin C deficiency). In the nineteenth century, it was shown that substituting un- polished for polished rice in a rice-based diet could prevent the development of beriberi (caused by vitamin B1 deficiency). In 1906, British biochemist F. Hopkins demonstrated that foods contained necessary “accessory factors” in addition to proteins, carbohydrates, minerals, and water. The word “vitamin” became a modern vocabulary term as shortened from the original word vitamine, as used by Polish chemist C. Funk in 1912 to describe the “vital amine” (a compound containing a nitro- gen bound to three hydrogen atoms [-NH3] that is vital to our health) antiberiberi accessory growth factor substance then discovered in unpolished rice. The term “vitamin” soon came to be applied to all accessory growth factors in general when many scientists identified, purified, and synthesized the thirteen vitamins and discovered that not all of the factors contained the nitrogen-based chemical amine groups. Vitamins were originally categorized based on their body function and assigned letter names to simplify discussion. As their chemical structures were deter- mined, chemical names were also used.

Human vitamin requirements are generally expressed in terms of the recommended dietary allowance (RDA). These RDA values, as established by the Food and Nutrition Board of the National Academy of Sciences/National Research Council in the United States and by the Food and Agriculture Organization and World Health Organization for different worldwide population groups, represent the amount of essential nutrients that, if acquired daily, are considered sufficient to meet the known nutritional requirements of most healthy individuals within the population. In some cases, the average requirements are not known with precision; RDA values are then based on average dietary intake within a population, plus extra as a margin of safety to account for increased demands (e.g., during illnesses, etc.). While once expressed in terms of international units, the strength of a vitamin or the amount of a vitamin necessary to produce a certain biological effect is currently expressed directly in micrograms or milligrams (metric weights). Many vitamins work together to regulate several body processes, and either an overabundance or insufficient amount of vitamins may potentially disturb the internal balance, or homeostasis, within the body and potentially lead to a disease state or, in some cases, death.

Fat-soluble vitamins, including A, D, E, and K, seem to have highly specialized functions. The intestine absorbs fat-soluble vitamins, and the lymphatic system transports these vitamins to various body regions. Be- cause fat-soluble vitamins easily dissolve in lipids (fats), hydrocarbons, and similar solvents, they normally diffuse through the cell membranes and into other lipids of the body, including adipose (fat) tissue and the lipid inclusions within the liver. Thus, the body usually maintains a significant storage reserve of these vitamins, and normal metabolism may persist for quite a long time (usually several months) after dietary sources of these vitamins have been excluded.