Vitamin B12 concentrations in milk from Norwegian women during the six first months of lactation

Authors: HENJUM, SIGRUN - University Of Oslo; MANGER, MARIT - Children'S Hospital Oakland Research Institute; HAMPEL, DANIELA - University Of California, Davis; BRANTSÆTER, ANNE - The Norwegian Institute Of Public Health; Shahab-Ferdows, Setti; BASTANI, NASSER - University Of Oslo; STRAND, TOR - University Of Bergen; REFSUM, HELGA - University Of Oslo; Allen, Lindsay - A

Submitted to: European Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/2020
Publication Date: 1/30/2020
Citation: Henjum, S., Manger, M., Hampel, D., Brantsæter, A.L., Shahab-Ferdows, S., Bastani, N.E., Strand, T.A., Refsum, H., Allen, L.H. 2020. Vitamin B12 concentrations in milk from Norwegian women during the six first months of lactation. European Journal of Clinical Nutrition. 74:749-756. https://doi.org/10.1038/s41430-020-0567-x.
DOI: https://doi.org/10.1038/s41430-020-0567-x

Interpretive Summary: Little is known about maternal and milk vitamin B12 concentrations in high-income countries. Therefore, we measured vitamin B12 in milk during the first 6 months postpartum in 175 Norwegian women and investigated its relationship to maternal B12 consumption, and maternal urinary methylmalonic acid (MMA), a B12 indicator, as well as creatinine-adjusted MMA (MMA/Cr). We found that the average milk B12 concentration was 327 pmol/L (range 140–1089), and mothers daily B12 intake was 5 µg. The use of B12 supplements had no effect on milk B12, and MMA/Cr was low in all women. When mothers were exclusively breastfeeding, MMA/Cr and lactation stage were identified as predictors of human milk B12 concentrations. We did not observe any relationships between total B12 intake of the mothers and milk B12 concentration, or between total B12 intake and MMA/Cr. Thus, in our study population, the maternal B12 status and human milk B12 concentrations are likely sufficient, given that the mother sufficiently consumed B12 and by their low urinary MMA concentrations. Even though maternal B12 status did not change during the first 6 months of lactation, their milk B12 concentration declined during the same time window, reducing the amount of B12 available to the infant through the milk.

Technical Abstract: Background: Human milk vitamin B12 (B12) concentrations depend on maternal status and intake; only few data are available in high-income countries. Objective: We assessed human milk B12 concentrations during the first 6 months postpartum in Norwegian women and its association with maternal dietary B12 intake and maternal urinary methylmalonic acid (MMA) concentration. Methods: In this cross-sectional study, 175 mothers, exclusively (80%) or partially (20%) breastfeeding, were included. Milk B12 was measured by IMMULITE®/IMMULITE® 1000 B12 competitive protein binding assay and urinary MMA relative to creatinine (MMA/Cr) by liquid chromatography–tandem-mass spectrometry. Maternal habitual B12 intake and supplement use were estimated using a food frequency questionnaire. Results: Mean human milk B12 concentration was 327 pmol/L (range 140–1089), with 402 pmol/L at 1 month (n = 21), 333 pmol/L at four months (n = 32), and 299 pmol/L at 6 months (n = 21). Maternal B12 intake was 5 µg/d, 89% met the Estimated Average Requirement, and supplement use did not affect milk B12 concentrations. MMA/Cr was low in all women compared with published data. In exclusively breastfeeding women, MMA/Cr (beta (95% CI) -42.5 (-82.5, -2.5) and time since birth (-4.9 (-9.6, -0.3)) were significant predictors of human milk B12 concentrations. There was no association between total B12 intake and milk B12 concentration or between total B12 intake and MMA/Cr. Conclusions: Maternal B12 status and human milk B12 concentrations are likely sufficient, based on adequate maternal B12 dietary intake combined with low urinary MMA concentrations. Nevertheless, milk B12 concentration fell during 6 months postpartum while maternal B12 status did not change.