D A Bender, University College London, London, UK © 2005 Elsevier Ltd. All rights reserved.
Vitamin B6 has a central role in amino acid metabolism as the coenzyme for a variety of reactions, including transamination and decarboxylation. It is also the coenzyme of glycogen phosphorylase and acts to modulate the activity of steroid and other hormones (including retinoids and vitamin D) that act by regulation of gene expression.
Severe deficiency disease has only been reported in a single outbreak in infants fed overheated formula. However, a significant proportion of people in developed countries have marginal vitamin B6 status, and this may be associated with enhanced responsiveness to steroid hormone action and may be a factor in the development of hormone-dependent cancer of the breast, uterus, and prostate. A number of drugs have antivitamin activity, and prolonged use may lead to secondary development of pellagra, as a result of impaired tryptophan metabolism.
Estrogens do not cause vitamin B6 deficiency. However, there is evidence that high doses of vitamin B6 may overcome some of the side effects of estrogenic steroids used in contraceptives and as menopausal hormone replacement therapy. At very high levels of intake, supplements may cause sensory nerve damage.
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