Pyridoxine is 3-hydroxy 4,5 dihydroxy methyl - 2- methyl pyridine (Fig 8.8) The metabollically active form of vitamin B6 is pyridoxal phosphate.
Three forms of vitamin B6 exist in nature which are pyridoxine, pyridoxal and pyridoxamine. The functions of vitamin B6 are closely related to protein metabolism, the synthesis and breakdown of amino acids, conversion of tryptophan to niacin, the production of antibodies, the formation of heme in hemoglobin, the formation of hormones important in brain function and others.
Meat, especially organ meats, whole grain cereals, peanuts and wheat germ are rich sources. Milk and green vegetables supply smaller amounts.
Although most of the body’s vitamin B6 is associated with glycogen phosphorylase in muscle, this is relatively stable and well conserved.
The requirement depends not on energy expenditure and glycogen metabolism, but on the intake of protein. The average requirement is 13 μg/g dietary protein.
Infants - 0.3 mg / day
Children - 0.6 - 1.2 mg / day
Adults - 1.6 - 2 mg/day
Pregnant and lactating women - 2.5 mg/day
Pyridoxine is readily absorbed from the small intestine. The excess amount if ingested is not stored in the body but is excreted in urine.
Deficiency of vitamin B6 is extremely rare. Nervous disturbances such as irritability, insomnia, muscular weakness, fatigue and convulsion have been recorded in infants. The cause of the convulsions severe impairment of the activity of the enzyme glutamate decarboxylase, which is dependent on pyridoxal phosphate. The product of glutamate decarboxylase is GABA (γ-amino butyric acid) which is a regulatory neurotransmitter in the central nervous system.