Vitamins

 

Vitamins are chemically unrelated organic compounds that cannot be synthesized in adequate quantities by humans and, therefore, must be supplied by the diet. nine vitamins ( folic acid, cobalamin, ascorbic acid, phyridoxine, thiamine, niacin, riboflavin, biotin, and pantothenic acid) are classified as water-soluble, whereas four vitamins ( vitamins A,D, K and E) are termed fat-soluble ( Figure 28-1) Vitamins are required to per-form specific cellular functions, for example many of the water-soluble vitamins are precursors of coenzymes for the enzymes of intermediary soluble vitamins ( vitamin K) has coenzyme function, there vitamins are released, absorbed, and transported with the fat of the diet, they are not readily excreted in the urine, and significant quantities are stored in the liver and adipose tissue. infect, consumption of vitamins A and D in excess of the recommended dietary allowances can lead to accumulation of toxic quantities of these compounds,