Vitamin B12 metabolism and status during pregnancy, lactation and infancy.

This overview of vitamin B12 metabolism and requirements during the continuum of pregnancy and lactation has identified several gaps in our knowledge. More information is needed concerning the roles of the different transcobalamins during pregnancy and lactation, including their impact on placental and mammary transfer of cobalamin and their effect on intestinal absorption in the infant. Knowledge is needed about the relative importance of maternal stores and current dietary intake on fetal storage of the vitamin, and on its concentration in breast milk. Because there is some evidence that infant's urinary methylmalonic acid excretion is reduced by intakes slightly higher than the current RDA, the adequacy of the current RDA for vitamin B12 during infancy should be verified. Finally, it is possible that vitamin B12 deficiency is more common in pregnant and lactating women and their young children in developing countries than has been recognized previously, due primarily to malabsorption. It is important to confirm whether or not this is the case, in view of its potential impact on infant neurobehavioral development and the relative ease with which supplements of the vitamin could be provided.