The distribution of total vitamin B12, holotranscobalamin, and the active vitamin B12 fraction in the first 5weeks postpartum.

Abstract

Total vitamin B12 levels decrease significantly during pregnancy and recover to normal values within 8-week postpartum. Holotranscobalamin (holoTC) reflects the active part of vitamin B12 and has been shown to remain constant during pregnancy and postpartum. A mechanism of redistribution of vitamin B12 is suggested, with a shift toward holoTC if there is insufficient total vitamin B12 available. Our objective was to examine vitamin B12 deficiency and the active vitamin B12 fraction in postpartum women. Total vitamin B12 and holoTC were measured in 171 women within 48hours (T0) and at 5weeks (T5) postpartum. Vitamin B12 deficiency was defined as total vitamin B12<180pmol/L or holoTC <32pmol/L. The active vitamin B12 fraction was defined as holoTC/total vitamin B12. Without intervention, vitamin B12 deficiency based on both serum total vitamin B12 and holoTC changed from 75% and 60%, to respectively 10% and 6% at T5. The fraction of active vitamin B12 was significant higher in vitamin B12 deficient women at both time points and across time (P<.0001 and P=.002). A high fraction of active vitamin B12 was only present in women with total vitamin B12 deficiency at T0. At T5, no high vitamin B12 fraction was found. The changes in total vitamin B12 levels seem to be based on a physiological changes rather than vitamin B12 deficiency. The results of this study confirm the hypothesis that a shift toward the metabolic active vitamin B12 (holoTC) occurs in women with insufficient available total vitamin B12.