Sialic Acid in Human Milk and Infant Formulas in China: Concentration, Distribution, and Type

This study compared the concentrations, types, and distributions of sialic acid in human milk at different stages of the postnatal period with those in a range of infant formulas. Breast milk from mothers of healthy, full-term, and exclusively breastfed infants were collected on the 2nd (n=246), 7th (n=135), 30th (n=85), and 90th (n=48) day after birth. The sialic acid profiles of human milk, including their distribution, were analyzed and compared with 24 different infant formulas. Outcome of this observational study was the result of natural exposure. Only sialic acid of type Neu5Ac was detected in human milk. Total sialic acid concentrations were highest in colostrum and reduced significantly over the next three months. Approximately 68.7%-76.1% of all sialic acids in human milk were bound to oligosaccharides. Two types of sialic acids, Neu5Ac and Neu5Gc, have been detected in infant formulas. Most sialic acid was present in infant formulas combined with protein. Breastfed infants could receive more sialic acid than formula-fed infants with the same energy intake. Overall, human milk is a preferable source of sialic acid than infant formulas in terms of total sialic acid content, dynamics, distribution, and type. These sialic acid profiles in the natural state are worth to be considered by the production of formulas, because they may have a great effect on infant nutrition and development.