Main functions. PLP functions as a coenzyme for more than 160 different enzymatic reactions in the metabolism of amino acids, one-carbon reactions, glycogenolysis and gluconeogenesis, haem synthesis, niacin formation, and also in lipid metabolism, neurotransmitter synthesis and hormone action (Bjørke-Monsen & Ueland, 2023b; EFSA, 2016a; IOM, 1998b).
Indicator for recommended intake. Plasma PLP concentration reflects the tissue stores of vitamin B6 (biomarker of status) and has a defined cut-off value for an adequate vitamin B6 status (Bjørke-Monsen & Ueland, 2023b; EFSA, 2016a; IOM, 1998b).
Main data gaps. There are limitations in biomarkers of vitamin B6 intake and status, and information on the variability in the requirement is absent (EFSA, 2016a).
Deficiency and risk groups. Prolonged vitamin B6 deficiency, which is uncommon, is reported to cause peripheral neuropathy that leads to weakness, decreased reflexes, sensory loss, and ataxia, particularly in the lower limbs. Seizures, migraine, cognitive decline, and depression have also been linked to vitamin B6 deficiency (Bjørke-Monsen & Ueland, 2023b). Mean plasma values below 30 nmol/l are associated with perturbations of amino acid, lipid, and organic acid profiles in plasma (EFSA, 2016a).
Dietary reference values. Plasma PLP concentration is considered as the biomarker of status; it has a defined cut-off value for an adequate vitamin B6 status (30 nmol/l). AR is set to 1.3 mg/day in females based on balance studies, this was extrapolated to 1.5 mg/day in males (see Appendix 5). RI is set to 1.6 mg/day in females and 1.8 mg/day in males. UL is defined as 12.5 mg/d for both males and females (EFSA, 2023a).