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Plasma Vitamin B₆ Vitamers before and after Oral Vitamin B₆ Treatment: A Randomized Placebo-controlled Study

¹ Department of Clinical Biochemistry AKH, Aarhus University Hospital, Nørrebrogade 44, DK-8000 Aarhus C, Denmark.

² Department of Pharmacology,
³ Institute of Medicine, and
⁴ Locus for Homocysteine and related Vitamins, University of Bergen, N-5021 Bergen, Norway.

^aAuthor for correspondence. Fax 45-89493060; e-mail vakbor{at}hotmail.com.

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.

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