Carotenoids and vitamin A are nutrients crucial to infants’ development. To date, there is limited data on their availability in breastmilk and the associated dietary factors, especially in Hong Kong, where people follow a westernized Chinese diet. This study determined the selected breastmilk’s carotenoid and vitamin A (retinol) contents by ultraperformance liquid chromatography with photodiode detection (UPLC-PDA) and the dietary intakes by three-day food records in 87 Hong Kong lactating mothers, who were grouped into tertiles based on their daily carotenoid intake. Low vitamin A intake (530.2 ± 34.2 µg RAE/day) and breastmilk retinol level (1013.4 ± 36.8 nmol/L) were reported in our participants, suggesting a poor vitamin A status of the lactating participants having relatively higher socioeconomic status in Hong Kong. Mothers in the highest tertile (T3) had higher breastmilk carotenoid levels than those in the lowest (T1) (p < 0.05). There were significant associations between maternal carotenoid intakes and breastmilk lutein levels in the linear regression models (p < 0.05) regardless of dietary supplement intake. Furthermore, maternal dark green vegetable intakes were associated with breastmilk retinol, lutein, and β-carotene levels. These findings can serve as dietary references for lactating mothers to enhance breastmilk carotenoid and vitamin A contents for the benefits of child growth and development.

The nutritional contents of breastmilk (BM) directly participate in neonatal metabolism via breastfeeding. Currently, there is limited research on BM metabolites and proteins compositions, and their alterations during the long lactation period in Hong Kong mothers. In this study, liquid chromatography–mass spectrometry‐based metabolomics, lipidomics and proteomics studies were applied to compare the compositions in BM of Hong Kong lactating mothers at the 2nd, 6th, and 12th months after delivery. Distinct metabolomics and lipidomics signatures in 6th month versus 2nd month and 12th month versus 2nd month were observed, and a total of 19 differential metabolites and 105 lipids were identified. Metabolomics study showed the significant alterations in key pathways involved in biotin metabolism, amino acid, and fatty acid‐associated metabolisms. Lipidomics analysis indicated the accumulation of triglyceride and ceramide during the lactation period. The remodeling of glycerophospholipids was also observed during 12‐month period. Moreover, 28 differentially expressed proteins were identified and mainly associated with GO functions and KEGG pathways of ribosome and complement and coagulation cascades, which were validated by network analysis. Our research contributes to the understanding of the BM compositions and differences during the long lactation period in postpartum women of Hong Kong.