Background: Folate requirements increase during pregnancy and lactation. It is recommended that women who could become pregnant, are pregnant, or are lactating consume a folic acid (FA)-containing supplement. Objectives: We sought to determine breast-milk total folate and unmetabolized folic acid (UMFA) contents and their relation with FA-supplement use and doses in a cohort of Canadian mothers who were enrolled in the MIREC (Maternal-Infant Research on Environmental Chemicals) study. Design: Breast-milk tetrahydrofolate (THF), 5-methyl-THF, 5-formyl- THF, 5,10-methenyl-THF, and UMFA were measured with the use of liquid chromatography-tandem mass spectrometry (n = 561). Total daily supplemental FA intake was based on self-reported FA-supplement use. Results: UMFA was detectable in the milk of 96.1% of the women. Total daily FA intake from supplements was associated with breast folate concentration and species. Breast-milk total folate was 18% higher (P , 0.001) in supplement users (n = 401) than in nonusers (n = 160), a difference driven by women consuming .400 mg FA/d (P ≥ 0.004). 5-Methyl-THF was 19% lower (P , 0.001) and UMFA was 126% higher (P , 0.001) in supplement users than in nonusers. Women who consumed .400 mg FA/d had proportionally lower 5-methyl-THF and higher UMFA than did women who consumed ≥400 mg FA/d. Conclusions: FA-supplement use was associated with modestly higher breast-milk total folate. Detectable breast-milk UMFA was nearly ubiquitous, including in women who did not consume an FA supplement. Breast-milk UMFA was proportionally higher than 5-methyl-THF in women who consumed .400 mg FA/d, thereby suggesting that higher doses exceed the physiologic capacity to metabolize FA and result in the preferential uptake of FA in breast milk. Therefore, FA-supplement doses .400 mg may not be warranted, especially in populations for whom FA fortification is mandatory.

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Keywords Breastmilk, Folate, Folic acid, Supplements, Unmetabolized folic acid
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Journal American Journal of Clinical Nutrition
Page, R. (Rachael), Robichaud, A. (André), Arbuckle, T.E. (Tye E.), Fraser, W.D. (William D.), & MacFarlane, A.J. (2017). Total folate and unmetabolized folic acid in the breast milk of a cross-section of Canadian women. American Journal of Clinical Nutrition, 105(5), 1101–1109. doi:10.3945/ajcn.116.137968