Vitamin B₆- A collective term for a group of water-soluble substances which include pyridoxine, pyridoxal and pyridoxamine. Pyridoxine, pyridoxal and pyridoxamine are all derivatives of pyradine and differ only in the functional group attached to this molecule. Pyridoxine occurs primarily in plants in comparison to pyridoxal and pyridoxamine, which are obtained from animal derived food. Pyridoxine, pyridoxal and pyridoxamine can equally serve as precursors of the biologically active enzyme, pyridol phosphate. Pyridoxal phosphate serves as a coenzyme in a number of reactions, particularly those involving the metabolism of amino acids and in the breakdown of glycogen. For example, histamine can be made from the amino acid histidine, from a reaction that requires pyridoxal phosphate.

Sources of vitamin B₆

Vitamin B₆ can be obtained from most foods, especially meat, liver, egg yolk, vegetables, and whole grain cereals.

RDA of vitamin B₆

The amount of pyridoxine required increases with the intake of protein. Since pyridoxine is involved with the metabolism of amino acids and proteins are composed of amino acids, more of the vitamin is required as protein intake increases. The RDA of pyridoxine is 2.2 mg (milligrams) for the adult males and 2.0 mg for adult females. This is based on a daily protein consumption of 100g. In individuals who participate in activities such as weighlifting, where increased amounts of protein are required and consumed, the amount of pyridoxine required additionally increases.

vitamin B₆ deficiency

Clinically overt deficiency of vitamin B₆ is rare but has been observed in newborns fed with formulas low in the vitamin, and in women taking oral contraceptives and in those suffering with alcoholism.

vitamin B₆ toxicity

Toxicity from vitamin B₆ from intakes of greater than 2 g/day (2000 mg/day) has been observed and is characterized by neurological symptoms.

vitamin B₆ interactions

Isoniazid, a drug used for the treatment of tuberculosis, can cause a vitamin B₆ deficiency. Isoniazid accomplishes this by forming an inactive derivative with pyridoxal phosphate, rendering the molecule useless. The action of levadopa, a drug used to treat parkinsonism, is antagonized by pyridoxine.