Concentration and distribution of sialic acid in human milk and infant formulas

Abstract

Human milk, including milk from mothers of preterm infants, is a rich source of oligosaccharide-bound sialic acid, which contrasts with the relatively small amounts found in infant formulas. The nutritional significance of sialic acid is presently unknown, but it is plausible that it is a conditional nutrient that contributes to sialic acid accretion in the brain.

The role and potential of sialic acid in human nutrition

“…In contrast, infant formulas contain most sialic acid bound to glycoproteins (70%) (Wang et al, 2001b). Carlson (1985) made similar observations.…”

“…We investigated the milk of 20 full-term mothers and 14 preterm mothers (mean gestational age 3173 weeks) at four stages of lactation (colostrum, transition, 1 and 3 months) and compared with 21 different formulas. A Bio-Gel P-2 column was used to separate sialic acid from milk and a colorimetric method was used to quantitate the amount (Wang et al, 2001b). We found total sialic acid levels were highest in colostrum (3.7270.15 mmol/l in full term and 4.2770.15 mmol/l in preterm) and decreased over time.…”

“…Both glycoprotein and glycolipid fractions of human milk contain lower levels of sialic acid than that of the free oligosaccharide fraction. Determination of sialic acid levels in infant formulas established that most sialic acid occurs in the glycoprotein fraction, and that the content of sialic acid in the oligosaccharide fraction is dependent on the whey: casein ratio of the formula (Neeser et al, 1991;Wang et al, 2001b). Bovine mature milk, which is currently used to produce infant formulas has a low sialic acid content of 0.05-0.62 mmol/l (Carlson, 1985;Neeser et al, 1991;Sanchez-Diaz et al, 1997;Wang et al, 2001b), equivalent to less than one-quarter of the level in mature human milk (1 month…”

“…The role and potential of sialic acid B Wang and J Brand-Miller lactation) (Wang et al, 2001b). Preterm formulas contained the most sialic acid (0.6370.12 mmol/l) followed by the 'follow-on' formulas (0.4370.03 mmol/l).…”

“…Cow's milkbased formulas containing 60% whey (ie whey:casein ratio in protein component ¼ 60:40) contained more sialic acid (0.3770.01 mmol/l) than those containing 20% whey (0.2170.02 mmol/l). The majority of sialic acid in infant formulas is bound to protein (70%) followed by free oligosaccharides (28%), with only 1% in the free form (Wang et al, 2001b). Thus infants fed bovine milk, bovine-based formula or soybean-derived formulas receive little or no sialic acid, while breast-fed babies receive an early diet rich in sialic acid.…”