This article presents an overview of vitamin B6, covering aspects such as physiological functions, factors leading to deficiency, health issues associated with insufficient vitamin B6 levels, dosage ranges, as well as adverse effects and label warnings related to vitamin B6.
Functions of Vitamin B6
Vitamin B6 is involved in various metabolic, biochemical and enzymatic functions, such as those in energy metabolism, cardiometabolic health, metabolism of homocysteine, nervous system, mental health, inflammation, oxidative stress, and immune system. Table 1 shows some of the functions of vitamin B6.
Vitamin B6 and Biochemical and Enzymatic Processes PLP-dependent enzymes catalyse more than 140 distinct enzymatic reactions. 5, 7, 17 Enzymes that depend on PLP exhibit significant diversity, and the reactions they catalyse are believed to account for approximately 4 % of all recognised catalytic activities. 8 Some examples of PLPdependent enzymatic reactions include the synthesis of putrescine from L-ornithine, leading subsequently to the synthesis of spermidine and other polyamines, and the conversion of serine to glycine and tetrahydrofolate to 5,10-methylenetetrahydrofolate. 8
Vitamin B6 plays a vital role in the metabolism of carbohydrates, lipids, amino acids, and nucleic acids. It facilitates glycogen degradation in conjunction with glycogen phosphorylase, serving as a coenzyme in the transamination and decarboxylation of amino acids, and participating in reactions catalysed by amino acid synthases or racemases. 9 PLPdependent enzymes are involved in fatty acid metabolism. 5, 7 The enzyme δ-6-desaturase catalyses the synthesis of vital polyunsaturated fatty acids by the desaturation of linoleic acid and γ-linolenic acid. 7 Enzymes that depend on PLP play a crucial role in amino acid metabolism by facilitating key reactions such as transamination, racemisation, decarboxylation, and α, β-elimination. 7
Vitamin B6 and Energy Metabolism PLP plays a major role in energy metabolism. 14 Vitamin B6 is involved in the metabolism of protein, carbohydrates and lipids, 9, 19 11, 19
and in gluconeogenesis and glycogenolysis. 11 PLP is an important cofactor for the metabolism of glycogen. 7, 24 The PLP-dependent glycogen phosphorylase mediates the breakdown of stored glycogen by the release of glucose from glycogen. 7 Glycogen can be mobilised within the cell through the action of glycogen or starch phosphorylase, an enzyme that relies on PLP and catalyses the hydrolysis of α-1,4-glycosidic bonds, resulting in the production of glucose-1- phosphate. 5 Vitamin B6 is essential for supporting mitochondrial function. 14
Vitamin B6 and Cardiometabolic Health Low plasma levels of PLP in humans have been associated with high-risk atherosclerosis, stroke, and thrombosis. 9 PLP-dependent enzymes are involved in haemoglobin formation. 7 The ratelimiting enzyme in haem biosynthesis is the PLP-dependent 5-aminolevulinate acid synthase. 10 Vitamin B6 might influence the influx of Ca2 + into cells through voltage-gated ATPdependent purinergic receptors, indicating its potential involvement in the management of hypertension and cardiac dysfunction. 9 PLP regulates various cardiometabolic processes, including the management of blood pressure through its effect on the renin-angiotensin system, as well as the mechanisms of blood coagulation, thereby maintaining endothelial integrity and facilitating platelet aggregation. 9 Vitamin B6 contributes to cardioprotection by influencing the actions of histamine, GABA, and imidazole dipeptides, as well as by inhibiting the P2 × 7R-NLRP3 inflammasome. 9 Studies indicate that the consumption of glucose by healthy individuals results in reduced PLP levels. 9 PLP plays a crucial role in maintaining the homeostasis of carnosine, homocarnosine, and anserine, which serve as cardioprotective agents possessing antioxidant and antiinflammatory characteristics. 9
Metabolism of one-carbon units 14, 16, 19-21 Trans-sulphuration 13, 16, 20, 22 Synthesis of amino acids 5, 8, 13, 16 Regulation of DNA synthesis 14 Metabolism of DNA 16 Nucleic acid synthesis 23 Thymidine biosynthesis 4 5, 7, 10, 11, 18, 24
Metabolism of amino acids Protein metabolism 17, 19 Protein synthesis 23 Metabolism of amine substrates 11 Transamination reactions 5, 7, 8, 23 Deamination reactions 23 Decarboxylation 7, 23 Racemisation 7, 23 Aminotransferases 14 Cystathionine β-synthase 22 Cellular proliferation 23 Carbohydrate metabolism 17, 19 8, 10, 15, 16
Glucose metabolism Fatty acid metabolism 8, 10 Lipid metabolism 13, 16, 17, 19 Gluconeogenesis 19 19, 22
Metabolism of homocysteine
Protein folding and stabilisation of |
Catabolism of amino acids 5, 8 |
Iron-sulphur( FeS) biosynthesis 14 |
de novo synthesis of NAD + 14 |
proteins 5 |
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|
|
Neurological development 19 Synthesis and metabolism of
Reduces
5, 10, 16 neurotransmitters corticosteroid release peripherally 4 Cell signalling 15
Synthesis of haem 4, 16 Formation of haemoglobin 19 Iron utilisation by red blood cells 4 Porphyrin synthesis 4
13, 16
Modulation of transcription factors Synthesis
of the methyl donor |
Interleukin-2 production 23 |
Immunocompetence 4 |
s-adenosylmethionine( SAM) 14 |
|
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T-Helper cell activation 23 Antibody production 23 Supporting mitochondrial function 14 Oestrogen metabolism 4
Antioxidant 16 |
Scavenging of reactive oxygen species 5 |
Reducing the formation of reactive |
|
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oxygen species 17 |
Table 1. Functions of Vitamin B6
Reducing the generation of advanced glycation end products( AGEs) 17
JATMS | Winter 2025 | 69