Vitamin B

Vitamin B6 is present in three forms: pyridoxal, pyridoxine, and pyridox-amine. All forms can be converted to the active vitamin-B6 coenzyme in the body. Pyridoxal phosphate (PLP) is the predominant biologically active form. Vitamin B6 is not stable in heat or in alkaline conditions, so cooking and food processing reduce its content in food. Both coenzyme and free forms are absorbed in the small intestine and transported to the liver, where they are phosphorylated and released into circulation, bound to albumin for transport to tissues. Vitamin B6 is stored in the muscle and only excreted in urine when intake is excessive.

PLP participates in amino acid synthesis and the interconversion of some amino acids. It catalyzes a step in the synthesis of hemoglobin, which is needed to transport oxygen in blood. PLP helps maintain blood glucose levels by facilitating the release of glucose from liver and muscle glycogen. It also plays a role in the synthesis of many neurotransmitters important for brain function. This has led some physicians to prescribe megadoses of B6 to patients with psychological problems such as depression and mood swings, and to some women for premenstrual syndrome (PMS). It is unclear, however, whether this therapy is effective. PLP participates in the conversion of the amino acid tryptophan to niacin and helps avoid niacin deficiency. Pyridoxine affects immune function, as it is essential for the formation of a type of white blood cell.

Populations at risk of vitamin-B6 deficiency include alcoholics and elderly persons who consume an inadequate diet. Individuals taking medication to treat Parkinson's disease or tuberculosis may take extra vitamin B6 with physician supervision. Carpal tunnel syndrome, a nerve disorder of the wrist, has also been treated with large daily doses of B6. However, data on its effectiveness are conflicting.

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