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

J Nutr. 2015 Jul;145(7):1507-14. doi: 10.3945/jn.115.210757. Epub 2015 May 20.


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 ∼8.6 μg/d [mixed diet (∼6 μg/d) plus a prenatal multivitamin supplement (2.6 μg/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 ∼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 ∼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 (∼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 as NCT01127022.

Keywords: controlled feeding study; holotranscobalamin; homocysteine; lactation; methylmalonic acid; pregnancy; reproductive state; vitamin B-12; women of reproductive age.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Biomarkers / blood
  • Breast Feeding
  • Choline / administration & dosage
  • Choline / blood
  • Dietary Supplements
  • Dose-Response Relationship, Drug
  • Double-Blind Method
  • Energy Intake*
  • Female
  • Healthy Volunteers
  • Homocysteine / blood
  • Homocysteine / urine
  • Humans
  • Lactation / blood
  • Methylmalonic Acid / blood
  • Micronutrients / administration & dosage*
  • Postpartum Period
  • Pregnancy
  • Recommended Dietary Allowances
  • Vitamin B 12 / administration & dosage
  • Vitamin B 12 / blood*
  • Young Adult


  • Biomarkers
  • Micronutrients
  • Homocysteine
  • Methylmalonic Acid
  • Choline
  • Vitamin B 12

Associated data