Plasma vitamin B6 vitamers before and after oral vitamin B6 treatment: a randomized placebo-controlled study

Background: Vitamin B6 has attracted renewed interest because of its role in homocysteine metabolism and its possible relation to cardiovascular risk. We examined the plasma B6 vitamers, pyridoxal 5′-phosphate (PLP), pyridoxal (PL), pyridoxine (PN), and 4-pyridoxic acid (4-PA) before and after vitamin B6 supplementation. Methods: Patients (n = 90; age range, 38–80 years) undergoing coronary angiography (part of the homocysteine-lowering Western Norway B-Vitamin Intervention Trial) were allocated to the following daily oral treatment groups: (A), vitamin B12 (0.4 mg), folic acid (0.8 mg), and vitamin B6 (40 mg); (B), vitamin B12 and folic acid; (C), vitamin B6; or (D), placebo. EDTA blood was obtained before treatment and 3, 14, 28, and 84 days thereafter. Results: Before treatment, PLP (range, 5–111 nmol/L) and 4-PA (6–93 nmol/L) were the predominant B6 vitamers identified in plasma. During the 84-day study period, the intraindividual variation (CV) in patients not treated with vitamin B6 (groups B and D) was 45% for PLP and 67% for 4-PA. Three days after the start of treatment, the increases in concentration were ∼10-, 50-, and 100-fold for PLP, 4-PA, and PL, respectively. No significant additional increase was observed at the later time points. The PLP concentration correlated to the concentrations of 4-PA and PL before treatment, but not after treatment. The PL concentration correlated with 4-PA before and after treatment. Conclusions: Vitamin B6 treatment has an immediate effect on the concentrations and the forms of B6 vitamers present in plasma, and the changes remain the same during prolonged treatment. Our results suggest that the B6 vitamers in plasma reflect vitamin B6 intake.