The oligosaccharide composition of human milk: temporal and individual variations in monosaccharide components

Oligosaccharides are an important component of human milk, but little is known about variations in their composition. The aim of this study was to determine the temporal and inter-individual variations in carbohydrate composition of human milk during the first 3 months of lactation. Serial milk samples of 10 mothers (eight full-term and two preterm births) were analyzed to determine the concentration of lactose and three monosaccharide components derived from the non-lactose carbohydrate: sialic acid, N-acetylglucosamine, and fucose. In full-term milk, sialic acid and N-acetylglucosamine were found to decrease significantly (p < 0.05) from weeks 1 to 13 postnatally. On average (mean +/- SD), sialic acid decreased by 71% (from 879 +/- 157 to 256 +/- 82 mg/L; p < 0.05) and N-acetylglucosamine by 56% (from 1,459 +/- 282 to 646 +/- 214 mg/L; p < 0.05), while fucose decreased by only 35% (from 660 +/- 192 to 432 +/- 180 mg/L; p > 0.05). On average, lactose concentration increased by 17% over the same period, from 55.4 +/- 4.2 g/L in week 1 to 64.9 +/- 2.3 g/L at 3 months. Preterm milk contained higher concentrations of each component, but temporal changes were similar to those seen in full-term milk. Apart from temporal changes, there were large inter-individual differences in oligosaccharide composition: fucose varied four-fold, sialic acid threefold, and N-acetylglucosamine two-fold among women at the same stage of lactation. The changes observed may simply reflect the aging of the cells responsible for milk secretion, but they are also consistent with a programmed adaptation of the milk composition to the needs of the infant.