Moderately low vitamin B 12 does not compromise transmethylation in adults on a free diet: implications for assessment of vitamin B 12 status

Abstract

Lower reference limits for vitamin B₁₂ are often defined solely in relation to haematological criteria. This may be misleading and there is evidence indicating that biochemical anomalies should also be considered. In 50 patients we measured creatine, as the major product of B₁₂-mediated remethylation, to see if this helps the definition of the B₁₂ reference interval and to investigate the possible effect of low B₁₂ on essential transmethylation. Vitamin B₁₂ values were grouped into six fractiles covering the range 50-500 ng/L; the corresponding creatine results were assessed by analysis of variance giving F=0·94 and a significance of 0·466. Although no correlation between B₁₂ and creatine was found, and therefore no obvious effect on transmethylation of low B₁₂ concentration, this must be interpreted with respect to methionine availability. Other factors indicate that biochemical perturbations should be taken into account when defining vitamin B₁₂ reference intervals.