Vitamin B6: A group of closely related chemical compounds with related names -- pyridoxine, pyridoxal and pyridoxamine -- that are transformed within the body to yet another form of vitamin B6, pyridoxal phosphate, that acts as a coenzyme. (A number of vitamins serve as coenzymes, substances that enhance the action of enzymes and thereby aid in catalyzing biochemical reactions.)
The vitamin B6 group is especially important to the function of the central nervous system, skin, and blood. Vitamin B6 is involved in the formation of red blood cells since pyridoxal phosphate is the rate-limiting substance in making heme, a component of hemoglobin, the key oxygen-carrying pigment in red blood cells.
The diet rarely lacks vitamin B6. Most foods contain it. However, deficiency of vitamin B6 within the body may occur due to poor absorption of it from the intestine or inactivation of it by some drugs (e.g., anticonvulsants, corticosteroids, estrogens, isoniazid, and penicillamine). Other causes of vitamin B6 include alcoholism and conditions such as hyperthyroidism and diabetes that increase the metabolic demand, creating a relative shortage of vitamin B6.
Vitamin B6 deficiency causes convulsions in infants and anemia in adults. An outbreak of convulsions in infants followed the inadvertent destruction of vitamin B6 in infant formulas. Several genetic syndromes also involve problems with vitamin B6.