Is sialic acid in milk food for the brain?

Abstract The rapid brain growth of infants places exceptionally high demands on the supply of nutrients from the diet. Human milk is the best source of food for brain growth and cognition. One of nature's richest sources of sialic acid, a vital component of brain gangliosides and the building block of polysialic acid (PSA) on neural cell adhesion molecule (NCAM), is found in human breast milk. However, infant formulas contain very little amounts. Gangliosides and polysialylated NCAM in the brain have an important role in cell-to-cell interactions, neuronal outgrowth, modifying synaptic connectivity, and memory formation. An exogenous source of sialic acid may be critical under conditions of extremely rapid brain growth, particularly during the first months after birth. Here we review the major differences in sialic acid concentration between human milk and infant formulas, and how sialic acid-bearing nutrients are metabolized. The role of this essential micronutrient in the developing brain is examined, particularly with respect to PSA, which has a major effect on brain plasticity.