VITAMIN B6

a water-soluble organic compound that is an essential micronutrient for microorganisms and animals. It occurs in three forms: pyridoxine (or pyridoxol), pyridoxal, and pyridoxamine. Pyridoxine was first isolated in 1938 and synthesized in 1939. Pyridoxal and pyridoxamine, which were discovered in the 1940s, are responsible for most of the vitamin B6 activity in organisms. Vitamin B6 is active in its coenzyme form of pyridoxol phosphate and functions in the formation and breakdown of amino acids, and hence indirectly of protein, in living tissues. It is also involved in the synthesis of serotonin and norepinephrine (two neurotransmitters) and of heme (a molecular constituent of hemoglobin). No human disease has been found to be caused by a deficiency of vitamin B6 in the diet, although certain human ailments of obscure origin respond to its administration. In experimental animals, vitamin B6 deficiency produces symptoms that depend to some extent on the other constituents of the diet; e.g., the skin lesions in rats may not appear if certain fats are present in the food. About 1950 vitamin B6 deficiency was produced experimentally in human infants. In infants the deficiency first manifests itself in a convulsion that is readily controlled by administration of the vitamin. Many cases of such convulsions have been reported in infants fed a human-milk substitute with insufficient amounts of vitamin B6. Because heat treatment of cows' milk destroys the vitamin, the deficiency can be corrected by altering the processing of the milk. An adult human needs 2.0 to 2.2 mg of vitamin B6 daily. Pyridoxal, pyridoxamine, and pyridoxine are equally effective in the nutrition of animals, although in microorganisms pyridoxal and pyridoxamine are much more active than pyridoxine. Vitamin B6 is widely distributed in foodstuffs and is particularly abundant in cereal grains, meats, nuts, and some fruits and vegetables.