We are gratified by the interest expressed by Drs Fischer, Thacher, and Pettifor regarding our recent article1 and the important problem of vitamin D deficiency in young children. We respect each of them as experts in this field and particularly welcome the global context that they provide.
First, we appreciate the point raised about the potential presence of vitamin D deficiency in the mothers of the infants studied. This variable was not examined in our study and would have been informative. There are data that suggest that breast milk is deficient in vitamin D, often related to the presence of this deficiency in mothers.2- 4 When a mother is vitamin D–depleted, she cannot excrete adequate concentrations of the vitamin into breast milk to prevent deficiency in an infant. Infants with mothers who are vitamin D–deficient may be deficient both in utero and during early infancy. Without vitamin D supplementation after birth, a breastfed infant remains or may become even more severely deficient. In parts of the world where food is scarce, this becomes particularly problematic. Considering this global context, some means of providing extra vitamin D to deficient infants and toddlers is clearly needed, either through sunlight, supplementation for those infants who are breastfed, or provision of fortified formula/milk for toddlers. We also appreciate the point raised about the prevalence of calcium deficiency in both this country and other parts of the world and its effect on vitamin D metabolism and therefore supplemental needs.