Milk folate secretion is not impaired during iron deficiency in humans.

The purpose of this study was to examine whether maternal iron and/or folate status influences human milk folate secretion and is responsible for growth faltering of Otomi infants in Capulhuac, Mexico. Breast-feeding mothers (n = 71) were randomized at 22 +/- 13 d (baseline) postpartum to receive a daily multivitamin supplement containing folic acid (400 microg) with and without iron (18 mg). Mothers provided blood and milk samples at baseline, and at 82 +/- 15 and 138 +/- 18 d postpartum. Iron supplementation significantly improved hematocrit and transferrin receptor concentrations but had no influence on maternal folate status or milk folate or iron concentrations. Forty-three percent of mothers (29/68) had low blood folate concentrations at baseline, whereas only 6% (4/66) had low blood folate concentrations at approximately 138 d postpartum. Milk folate concentrations did not differ between Fe-deficient and Fe-sufficient women and provided adequate levels of dietary folate by approximately 82 d postpartum. While milk iron concentrations were unrelated to maternal iron status, they decreased during lactation, and, by approximately 138 d, they provided only 55% of the current recommendation. In conclusion, milk folate concentrations appear to be well preserved during maternal iron deficiency; hence, faltering growth among infants in Capulhuac, Mexico is unlikely the result of reduced milk folate concentration secondary to maternal Fe deficiency. However, milk Fe concentrations showed a temporal decline. Whether the disjuncture between recommended and actual Fe intakes among infants born with low Fe reserves and weaned to foods low in bioavailable Fe has functional consequences is worthy of further investigation.