Another group of essential nutrients is the vitamins. Like essential amino acids and fatty acids, vitamins are carbon compounds that an animal requires for its normal growth and metabolism, but cannot synthesize for itself. Most vitamins function as coenzymes or parts of coenzymes and are required in very small amounts, compared with the essential amino acids and fatty acids, which have structural roles.
The list of vitamins varies from species to species. Most mammals, for example, can make their own ascorbic acid (vitamin C). However, primates (including humans) do not have this ability, so for primates, ascorbic acid is a vitamin. If we do not get vitamin C in our food, we develop a disease known as scurvy, characterized by bleeding gums, loss of teeth, subcutaneous hemorrhages, and slow wound healing. Scurvy was a serious and frequently fatal problem for sailors on long voyages until a Scottish physician, James Lind, discovered that the disease could be prevented if the sailors ate fresh greens or fresh fruit. Eventually the British Admiralty made limes standard provisions for its ships, and ever since, British sailors have been called "limeys." The active ingredient in limes was named ascorbic ("without scurvy") acid.
Humans require 13 vitamins. Table 50.2 lists these vitamins, their dietary sources, and their functions. They are di
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