New Insights into Human Milk Oligosaccharide Profiles in China: Findings from a Large-Scale Analysis of Human Milk

Background/Objectives: This study systematically analyzed the concentration dynamics of human milk oligosaccharides (HMOs) and the distribution characteristics of secretory (Se) and Lewis (Le) phenotypes in China. Methods: A total of 1462 breast milk samples were collected from lactating mothers in six major regions of China, including Changchun, Lanzhou, Chengdu, Tianjin, Guangzhou, and Shanghai. We quantified 17 major HMOs by high-performance anion exchange chromatography-pulsed amperometric detection (HPAEC-PAD), and Se/Le phenotypes were determined to evaluate regional differences and distribution patterns. Results: Total HMO concentration in breast milk showed a significant downward trend within 200 days postpartum and stabilized after 200 to 400 days. Fucosylated HMOs accounted for the highest proportion 60.0-83.0%, among which 2'-FL had the largest concentration 903.4-2832.7 mg/L; acetylated HMOs 8.4-17.6% and sialylated HMOs 8.2-25.3% accounted for relatively lower proportions. This study further divided breast milk into four phenotypes based on HMO characteristics: 72.49% of the samples were Se+/Le+, 6.145% were Se+/Le-, 20.12% were Se-/Le+, and 1.24% were double negative (Se-/Le-). Se+ and Le+ phenotypes accounted for 78.7% and 92.6% of the total population, respectively. The total concentration of HMOs in breast milk of different phenotypes was significantly different, with the average total HMO concentration of Se+/Le+ breast milk being the highest (8342 mg/L), while that of Se-/Le- breast milk being the lowest (4532 mg/L). Se+ phenotype was associated with higher levels of fucosylated HMOs, including 2'-fucosyllactose (2'-FL) and lacto-N-fucopentaose I (LNFP I), and lower levels of lacto-N-tetraose (LNT) and sialyl-lacto-N-tetraose b (LST b) compared to other phenotypes. Most HMOs reached their highest concentrations during the colostrum (CM) and transitional milk (TM) stages, followed by a progressive decline with lactation, with phenotype-specific variations evident across all HMOs. Notably, certain HMOs, such as 3-FL, 3'-SL, DFL, and LNDFH II, exhibited distinct temporal patterns. Conclusions: This study revealed the Se/Le phenotype distribution and dynamic characteristics of HMOs in the Chinese mother-infant population, offering a valuable reference for global breast milk composition databases and infant nutrition research.