Vitamin B6 Deficiency

Overview :

Vitamin B₆ is a water-soluble vitamin. The recommended dietary allowance (RDA) for vitamin B₆ is 2.0 mg/day for the adult man and 1.6 mg/day for the adult woman. Vitamin B₆ in the diet generally occurs as a form called pyridoxal phosphate. In this form, it cannot be absorbed by the body. During the process of digestion, the phosphate group is removed, and pyridoxal is produced. However, the body readily absorbs pyridoxal, and converts it back to the active form of the vitamin (pyridoxal phosphate).

Poultry, fish, liver, and eggs are good sources of vitamin B₆, comprising about 3-4 mg vitamin/kg food; meat and milk contain lesser amounts of the vitamin. The vitamin also occurs, at about half this level, in a variety of plant foods, including beans, broccoli, cabbage, and peas. Vitamin B₆ tends to be destroyed with prolonged cooking, with storage, or with exposure to light.

As mentioned, vitamin B₆ takes various forms. One of these forms, called pyridoxine, is relatively stable. For this reason, pyridoxine is the form of vitamin B₆ that is used in vitamin supplements, or when foods are fortified. Apples and other fruits are poor sources of the vitamin, containing only 0.2-0.6 mg vitamin/kg food.

Vitamin B₆, used mainly in the body for the processing of amino acids, performs this task along with certain enzymes. The enzyme that participates in this type of complex is aminotransferase. Several types of aminotransferase exist. With vitamin B₆ deficiency, while aminotransferase continues to occur in the various organs of the body, there is an abnormally low level of the active vitamin B₆/aminotransferase complex present. Thus, this vitamin deficiency results in the impairment of a variety of activities in the body. With supplement correction of the vitamin B₆ deficiency, the aminotransferase then readily forms the active complex, and normal metabolism is restored.

Vitamin B₆ converts certain amino acids (glutamic acid, aspartic acid, glycine) to energy. This allows the body to process all dietary protein, even when the dietary protein is in excess of the body's needs. Vitamin B₆ also allows the body to synthesize certain amino acids. For example, if the diet is deficient or low in certain amino acids, such as glycine or serine, vitamin B₆ enables the body to make them from sugar. Vitamin B₆ is used also for the synthesis of certain hormones, such as adrenaline.