Unmetabolized folic acid and total folate concentrations in breast milk are unaffected by low-dose folate supplements

Abstract

BackgroundMany lactating women in North America are exposed to high synthetic folic acid intakes because of food fortification and vitamin supplement use. Few data exist on the potential long-term effect of high folic acid intakes on milk folate concentrations, whereas no data are available on the effect of supplemental [6S]-5-methyltetrahydrofolate ([6S]-5-methylTHF). ObjectiveThe aim of the present study was to investigate the effect of 3 treatments (placebo, folic acid, and [6S]-5-methylTHF) on milk folate and folate-binding protein (FBP) concentrations and to determine whether unmetabolized folic acid is present in milk. DesignIn this 16-wk randomized, placebo-controlled intervention, 69 lactating women were randomly assigned to receive [6S]-5-methylTHF (416 μg/d, 906 nmol/d) or a placebo, or were assigned to receive folic acid (400 μg/d, 906 nmol/d) within 1 wk postpartum. Total milk folate, FBP, and unmetabolized folic acid concentrations were measured at 16 wk. ResultsUnmetabolized folic acid was detected in 96% of milk samples tested representing ≈8% of total milk folate concentrations. Total milk folate, FBP, and the proportion of unmetabolized milk folic acid did not differ between treatments; however, FBP concentrations were significantly lower than those published before mandatory folic acid fortification of the food supply. ConclusionMaternal intake of synthetic folic acid leads to the appearance of unmetabolized folic acid in milk and, seemingly, a down-regulation of milk FBP synthesis. The impact of these changes on the bioavailability of folate in infants requires further exploration.