Inclusion Criteria:  Availability of informed verbal consent Plan to reside in the defined study area for the next 12 months Mothers intend to breastfeed their children for at least 8 months, and exclusively for 4 months  Exclusion Criteria:  Severe systemic illness requiring hospitalization Growth retardation Severe congenital malformations Plasma cobalamin concentration <148 pmol/L (These children will be treated for vitamin B12 deficiency and not included in the RCT, but will be included in the cohort design)