Background: The effects of high-dose folic acid (FA) supplementation in healthy individuals on blood folate concentrations and immune response are un

Background: Pregnant women with low cobalamin concentrations are unable to provide the necessary amount of cobalamin to their fetuses. The effect of low maternal cobalamin concentrations on transmethylation metabolism in pregnant women and their newborns is unknown. Objective: We investigated the relation between maternal and neonatal cobalamin concentrations and changes in total homocysteine (tHcy), S-adenosylmethionine (SAM), and S-adenosylhomocysteine (SAH). Design: Hematologic data and concentrations of cobalamin, red blood cell folate, serum folate, tHcy, methylmalonic acid, SAM, SAH, and other metabolites were measured in 119 serum specimens from pregnant Brazilian women (gestational age: 37–42 wk) and their newborns' placental veins at the time of delivery. Results: The tHcy concentrations were higher in placental vein serum from newborns whose mothers had low cobalamin. Serum SAH concentrations were elevated and serum SAM and methionine concentrations were decreased in pregnant women with lower cobalamin concentrations. SAM:SAH was significantly decreased in both cobalamin-deficient pregnant women and their newborns. Conclusions: Lower maternal cobalamin concentrations are associated with higher tHcy and lower SAM:SAH in newborns. Because SAM:SAH is closely linked with the activity of numerous enzymatic methylation reactions, these results suggest that methylation could be impaired in cobalamin-deficient pregnant women and their newborns.