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

Vitamin B(6) has attracted renewed interest because of its role in homocysteine metabolism and its possible relation to cardiovascular risk. We examined the plasma B(6) vitamers, pyridoxal 5'-phosphate (PLP), pyridoxal (PL), pyridoxine (PN), and 4-pyridoxic acid (4-PA) before and after vitamin B(6) supplementation.

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 B(12) (0.4 mg), folic acid (0.8 mg), and vitamin B(6) (40 mg); (B), vitamin B(12) and folic acid; (C), vitamin B(6); or (D), placebo. EDTA blood was obtained before treatment and 3, 14, 28, and 84 days thereafter.

Before treatment, PLP (range, 5-111 nmol/L) and 4-PA (6-93 nmol/L) were the predominant B(6) vitamers identified in plasma. During the 84-day study period, the intraindividual variation (CV) in patients not treated with vitamin B(6) (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 approximately 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.

Vitamin B(6) treatment has an immediate effect on the concentrations and the forms of B(6) vitamers present in plasma, and the changes remain the same during prolonged treatment. Our results suggest that the B(6) vitamers in plasma reflect vitamin B(6) intake.