Cobalamin and haptocorrin in human milk and cobalamin-related variables in mother and child: a 9-mo longitudinal study.

Background: Measurement of milk cobalamin is hampered by the high content of the cobalamin-binding protein haptocorrin, and limited data are available relating trustworthy measures of milk cobalamin to cobalamin status in healthy mothers and their children. Objectives: The objectives were to explore the concentration of cobalamin and haptocorrin in foremilk and hindmilk during the first 9 mo of lactation and to relate these results to biomarkers of an impaired cobalamin status of mother and child. Design: Milk samples from 25 mothers were collected at 2 wk, 4 mo, and 9 mo postpartum for the measurement of cobalamin and haptocorrin. Plasma samples from a larger cohort of lactating mothers (n. = 107) and their infants (n = 108) were collected at the same time points for the measurement of cobalamin, holotranscobalamin, total transcobalamin, total haptocorrin, and methylmalonic acid. Results: Median (range) concentrations of cobalamin in hindmilk were 760 (210-1880), 290 (140-690), and 440 (160-1940) pmol/L at 2 wk, 4 mo, and 9 mo, respectively; the respective haptocorrin concentrations were 25 (9-102), 22 (4-100), and 180 (30-460) nmol/L. We found slightly lower values in foremilk. A decrease in milk cobalamin at 4 mo was associated with decreases in plasma cobalamin (P < 0.0001) and holotranscobalamin (P < 0.0001) in the infants. Strong positive associations in paired maternal-infant cobalamin concentrations were found at all time points. Conclusions: Foremilk and hindmilk contained comparable amounts of cobalamin and haptocorrin, but marked changes were observed during 9 mo of lactation. At 4 mo, low concentrations of milk cobalamin mirrored biochemical changes in infants, which suggests an impaired cobalamin status and indicates that nutrition from only mother's milk may not be sufficient for the supply of cobalamin from this age. This trial was registered by the Danish Data Protection Agency at www.datatilsynet.dk/english as 2008-41-2185.