[Sialic acid in breast milk and infant formula food]

Sialic acid (N-acetylneuraminic acid, NANA) is an essential component of mucins, glycoproteins and gangliosides and therefore important for the function of cell membranes, membrane receptors and the normal development of the brain. The capacity of the metabolic pathway for the synthesis of sialic acid from glucose and other carbohydrate sources in preterm infants and term-born neonates is currently unknown.

In the present study the overall nutritional sialic acid supply of infants was analysed by means of HPLC-based determination of sialic acid concentrations in a total of 51 human milk samples obtained from nursing mothers at different stages of lactation. The data were compared with 3 commercial preterm infant formulas, 7 adapted infant formulas, 11 partially adapted infant formulas, 4 follow-up and 2 soy-based formulas.

The sialic acid concentration in colostrum and transitory human milk was 1300 +/- 322 mg/l. After the 10th day of lactation the concentration dropped to 983 +/- 455 mg/l (p < 0.01). Preterm infant formulas contained 197 +/- 31, adapted formulas 190 +/- 31, partially adapted formulas 100 +/- 33, follow-up formulas 100 +/- 33 and soy-based formulas 34 +/- 9 mg sialic acid/l, respectively.

Formula-fed infants obtain less than 20% of the amount of sialic acid supplied if breast-fed. A sufficient sialic acid supply may be essential in very-low-birth-weight infants and neonates at risk for the normal development of brain function.