Dynamic Variations in Endogenous Peptides in Chinese Human Milk Across Lactation and Geographical Regions

<b>Background/Objectives</b>: This study characterized the endogenous peptide profile of human milk from a Chinese multicenter cohort (<i>n</i> = 200 mothers) using the Orbitrap Fusion Lumos LC-MS/MS. <b>Methods</b>: Samples were collected across different lactation stages (2 and 6 months postpartum) and seven geographic regions (Beijing, Chengdu, Guangzhou, Jinhua, Lanzhou, Weihai, and Zhengzhou). <b>Results</b>: In total, 6960 peptides derived from 621 proteins were identified. Peptides from the polymeric immunoglobulin receptor (PIGR) were more abundant in the 2nd month than the 6th month, providing a high antimicrobial activity and immune functions for the infants. Moreover, region-specific variations were observed, with milk from Lanzhou exhibiting significantly higher levels of β-casein (CASB) and butyrophilin subfamily 1 member A1 (BTN1A1) peptides compared to other cities. <b>Conclusions</b>: Furthermore, maternal dietary intake of oils and total fat correlated positively with the intensity of specific antimicrobial peptides, including CASB_199-216, CASB_200-226, and CASB_201-226. Infant growth parameters were inversely correlated with several antimicrobial peptides, although CASB_200-225 demonstrated positive associations. These findings offer novel insights into the dynamics of endogenous peptides in human milk and may guide breastfeeding recommendations and infant formula design.