Dietary polyphenols are phytonutrients exhibiting multiple health benefits in humans including those in infants. However, data on breast milk (poly)phenolic composition are limited, especially among Asian populations. This study aimed to assess the levels of dietary polyphenols and their microbial-derived metabolites in the breast milk of Hong Kong lactating women, and how maternal diet correlated with the phenolic composition in breast milk. Breast milk samples from 89 healthy Hong Kong lactating women (aged 19–40 years) were collected. Maternal intake of plant-based foods and polyphenols was estimated through 3-day dietary records and the Phenol-Explorer database. Twelve commonly consumed polyphenols including their microbial-derived metabolites in breast milk were quantified using an optimized and validated UHPLC-MS/MS method. The effect of maternal intake on breast milk phenolic levels was then examined via the Pearson correlation test. The mean concentrations of individual phenolic compounds ranged from 5.1 nmol L⁻¹ (chlorogenic acid) to 731.5 nmol L⁻¹ (3,4-dihydroxybenzoic acid). Despite suboptimal intake of fruits and vegetables among our participants, breast milk phenolic levels were comparable to those of foreign populations. Significant correlations were found between dietary intake and multiple phenolics, particularly legume and daidzein (r = 0.33, P = 0.001), and tea and epicatechin (r = 0.30, P = 0.03). Regarding phenolic metabolites, 3,4-dihydroxyphenylacetic acid was significantly correlated with several polyphenols, particularly quercetin (r = 0.34, P = 0.002), and equol was exclusively correlated with daidzein (r = 0.46, P < 0.001). Our findings support that intake of plant-based foods significantly affects breast milk phenolic composition. Future investigation on the bioavailability and health outcomes in infants is warranted to substantiate the transferability of these bioactive phytonutrients from mother to child through lactation, and to promote maternal intake of polyphenol-rich foods.

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.