TThe active coenzyme forms of vitamin B6 are pyridoxal phosphate (PLP) and pyridoxamine 5’ phosphate (PMP). They play a vital role in the function of approximately 100 enzymes that increase the speed of (‘catalyze’) essential chemical reactions in the human body (1, 2, 3, 4, 5) and are involved in amino acid metabolism (5). For example, PLP functions as a coenzyme for an enzyme that catalyzes the release of glucose from stored glycogen (‘glycogen phosphorylase’), and is involved in reactions used to generate glucose from amino acids (‘gluconeogenesis’) (4, 5).
In the brain, neurotransmitters, such as ‘serotonin’, ‘dopamine’, and ‘gamma-aminobutyric acid’ (GABA) are synthesized using PLP-dependent enzymes (4).
PLP also functions as a coenzyme in the synthesis of heme, an iron-containing component of ‘hemoglobin’, found in red blood cells to transport oxygen throughout the body. PLP is able to bind to the hemoglobin molecule and affect its ability to pick up and release oxygen (42). However, the impact of this on normal oxygen delivery to tissues is not known (4).
PLP is a coenzyme for a critical reaction in the synthesis of vitamin B3, niacin, from the essential amino acid ‘tryptophan’; thus, adequate vitamin B6 decreases the requirement for dietary niacin (4).
Steroid hormones, such as ‘estrogen’ and ‘testosterone’, exert their effects in the body by binding to steroid hormone receptors in the nucleus of the cell and altering gene expression (‘transcription’). PLP binds to steroid receptors in a manner that inhibits the binding of steroid hormones, thus decreasing their effects. The binding of PLP to steroid receptors for estrogen, progesterone, testosterone, and other steroid hormones suggests that the vitamin B6 status of an individual may have implications for diseases affected by steroid hormones, including breast and prostate cancers (4).
PLP serves as a coenzyme for a key enzyme involved in the synthesis of nucleic acids. The effect of vitamin B6 deficiency on the function of the immune system may be partly related to the role of PLP in one-carbon metabolism.
The European Food Safety Authority (EFSA), which provides scientific advice to assist policy makers, has confirmed that clear health benefits have been established for the dietary intake of vitamin B6 in contributing to:
Authored by Dr Peter Engel in 2010, reviewed and revised by Angelika Friedel on 14.06.2017