This study investigated the variation in oligosaccharide levels in the breast milk of south Chinese mothers in a prolonged breastfeeding period of up to 400 days postpartum. A total of 488 breast milk samples were collected from 335 healthy mothers at five different time points: 0-5 days, 10-15 days, 40-45 days, 200-240 days, and 300-400 days postpartum. A high-performance anion-exchange chromatography-pulsed amperometric detector (HPAEC-PAD) was used to quantify 2'-fucosyllactose (2'-FL), 3-fucosyllactose (3-FL), lacto-N-tetraose (LNT), lacto-N-neotetraose (LNnT), 3'-sialyllactose (3'-SL) and 6'-sialyllactose (6'-SL). In this study, we found six oligosaccharides that were present in breast milk from 0 to 400 days postpartum. The median value ranges of individual oligosaccharide components in this study were 1013-2891 mg/L 2'-FL, 193-1421 mg/L 3-FL, 314-1478 mg/L LNT, 44-255 mg/L LNnT, 111-241 mg/L 3'-SL, and 23-602 mg/L6'-SL. HMO levels decreased over the lactation periods, except for 3-FL, which increased throughout lactation. The predominant fucosylated and sialylated HMOs were 2'-FL and 6'-SL at 40-45 days postpartum and changed to 3-FL and 3'-SL at 200-240 days postpartum. Results from this study showed that lactating women continue to provide their offspring with a high level of 2'-FL one year after delivery, suggesting that 2'-FL may play an important role for infants in early life. Our findings also provide further evidence in support of breastfeeding after one-year postpartum.
Keywords: breast milk; human milk oligosaccharides; lactational stages; variation.