The relationship between maternal serum and breast milk vitamin B12 concentrations in a primarly supplemented versus an unsupplemented group : assesed at eight weeks postpartum

BACKGROUND: Vitamin B12 is an essential nutrient for adequate infant growth and development and breast milk is the only dietary source of vitamin B12 to the exclusively breast-fed infant. Little is known on the relationship between maternal serum vitamin B12 and breast milk vitamin B12. A better understanding of this relationship will provide insight into the determinants of milk vitamin B12 concentrations, including maternal vitamin B12 supplementation, for optimal infant vitamin B12 status. OBJECTIVE: To determine the association between maternal serum and breast milk vitamin B12 concentrations at eight weeks postpartum in both a supplemented and unsupplemented population and to explore these associations with infant serum vitamin B12 concentrations in the supplemented group. METHODS: Vitamin B12 concentrations were measured in infant serum, maternal serum and breast milk samples (n=186) collected from two previous studies; in Canada (supplemented) and New Zealand (unsupplemented). Supplemented participants were provided with a prenatal supplement containing 12µg of vitamin B12 during pregnancy to eight weeks postpartum. Breast milk and maternal blood were available from both studies, with infant blood only available from the supplemented group. Serum samples were measured using an Elecsys immunoassay analyzer, while an IMMULITE chemiluminescence machine measured breast milk vitamin B12 concentrations. RESULTS: The supplemented group had significantly higher serum vitamin B12 concentrations (Geometric mean: 665pmol/l; 95%CI: 601,685) compared to the unsupplemented group (403pmol/l, 365, 445). Maternal serum vitamin B12 was associated with breast milk vitamin B12 in the supplemented and unsupplemented groups (r=0.577, p<0.0001; r=0.414 p=0.01, respectively). Infant serum vitamin B12 concentrations were associated with both maternal serum vitamin B12 (r=0.299 p=0.001) and breast milk B12 (r=337 p