Vitamins; Introduction, absorption and functions
Vitamins: Essential Dietary Components Vitamins are essential, organic substances needed in small amounts in the diet. They are not a source of energy. Instead, they aid in energy metabolism as well as in the growth, development, and maintenance of body tissues. During the first half of the 20th century, scientists identified each of the 13 vitamins now recognized as essential. For the most part, as the vitamins were discovered, they were named alphabetically: A, B, C, D and E. Later, some substances originally classified as B-vitamins were dropped from the list because they were shown to be non-essential substances. The B-vitamins originally were thought to have a single chemical form but turned out to exist in many forms. Thus, the label "vitamin B" now comprises 8 B-vitamins. Vitamins A, D, E and K dissolve in organic solvents, such as ether and benzene, and are referred as fat-soluble vitamins . The B-vitamins and vitamin C, in contrast, dissolve in water and refe...