Vitamin B-12 Status Differs among Pregnant, Lactating, and Control Women with Equivalent Nutrient Intakes

Background: Limited data are available from controlled studies on biomarkers of maternal vitamin B-12 status. Objective: We sought to quantify the effects of pregnancy and lactation on the vitamin B-12 status response to a known and highly controlled vitamin B-12 intake. Methods: As part of a 10-12 wk feeding trial, pregnant (26-29 wk gestation; n = 26), lactating (5 wk postpartum; n = 28), and control (nonpregnant, nonlactating; n = 21) women consumed vitamin B-12 amounts of similar to 8.6 mu g/d (mixed diet (similar to 6 mu g/d) plus a prenatal multivitamin supplement (2.6 mu g/d)]. Serum vitamin B-12, holotranscobalamin (bioactive form of vitamin B-12), methylmalonic acid (MMA), and homocysteine were measured at baseline and study-end. Results: All participants achieved adequate vitamin B-12 status in response to the study dose. Compared with control women, pregnant women had lower serum vitamin B-12 (-21%; P = 0.02) at study-end, whereas lactating women had higher (P=0.04) serum vitamin B-12 throughout the study (+26% at study-end). Consumption of the study vitamin B-12 dose increased serum holotranscobalamin in all reproductive groups (+16-42%; P <= 0.009). At study-end, pregnant (vs. control) women had a higher holotranscobalamin-to-vitamin B-12 ratio)P= 0.04) with similar to 30% (vs. 20%) of total vitamin B-12 in the bioactive form. Serum MMA increased during pregnancy (+50%; P< 0.001) but did not differ by reproductive state at study-end. Serum homocysteine increased in pregnant women (+15%; P = 0.009) but decreased in control and lactating women (-16-17%; P < 0.001). Despite these changes, pregnant women had similar to 20% lower serum homocysteine than the other 2 groups at study-end (P <= 0.02). Conclusion: Pregnancy and lactation alter vitamin B-12 status in a manner consistent with enhanced vitamin B-12 supply to the child. Consumption of the study vitamin B-12 dose (similar to 3 times the RDA) increased the bioactive form of vitamin B-12, suggesting that women in these reproductive states may benefit from vitamin B-12 intakes exceeding current recommendations. This trial was registered at clinicaltrials.gov as NCT01127022.