title: Unmetabolized folic acid and total folate concentrations in breast milk are unaffected by low-dose folate supplements.
abstract: BACKGROUND
  Many 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).
  
  
  OBJECTIVE
  The 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.
  
  
  METHODS
  In this 16-wk randomized, placebo-controlled intervention, 69 lactating women were randomly assigned to receive [6S]-5-methylTHF (416 microg/d, 906 nmol/d) or a placebo, or were assigned to receive folic acid (400 microg/d, 906 nmol/d) within 1 wk postpartum. Total milk folate, FBP, and unmetabolized folic acid concentrations were measured at 16 wk.
  
  
  RESULTS
  Unmetabolized folic acid was detected in 96% of milk samples tested representing approximately 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.
  
  
  CONCLUSIONS
  Maternal 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.
authors.affiliation: Physiology & Experimental Medicine, The Hospital for Sick Children, Toronto, ON, Canada. lisa.houghton@otago.ac.nz
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Houghton
authors.forename: Jimao
authors.initials: J
authors.lastname: Yang
authors.forename: Deborah L
authors.initials: DL
authors.lastname: O'Connor
mesh_terms: D000293:Adolescent; D000328:Adult; D001682:Biological Availability; D002352:Carrier Proteins / Q000378:metabolism*; D019587:Dietary Supplements; D004311:Double-Blind Method; D005260:Female; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000008:administration & dosage* / Q000032:analysis* / Q000378:metabolism; D005527:Food, Fortified; D006801:Humans; D007774:Lactation / Q000378:metabolism*; D008895:Milk, Human / Q000737:chemistry*; D011247:Pregnancy; D011956:Receptors, Cell Surface / Q000378:metabolism*; D013763:Tetrahydrofolates / Q000008:administration & dosage* / Q000032:analysis* / Q000378:metabolism; D014803:Vitamin B Complex / Q000008:administration & dosage / Q000032:analysis / Q000378:metabolism; D055815:Young Adult
chemical_list: D002352:Carrier Proteins; D058973:Folate Receptors, GPI-Anchored; D011956:Receptors, Cell Surface; D013763:Tetrahydrofolates; D014803:Vitamin B Complex; D005492:Folic Acid; C005984:5-methyltetrahydrofolate