Mineral composition of donor human milk and its associations with maternal and infant factors in a Japanese population

Mineral composition of donor human milk (DHM) is important for the nutritional management of preterm infants, but data remain limited, particularly in Asian populations. This study determined calcium (Ca), inorganic phosphorus (IP), and zinc (Zn) concentrations in DHM from a Japanese human milk bank and their associations with maternal and infant factors. We analyzed 457 DHM samples from 331 donors, including 106 preterm and 351 term samples. Mineral concentrations were measured by a colorimetric assay, and associations with maternal and infant factors were evaluated using linear mixed-effects models accounting for repeated samples. Zn concentrations were higher in preterm DHM than in term DHM in the unadjusted comparison (141 [100–183] µg/dL vs. 113 [72–147] µg/dL, p < 0.001), but the difference was not significant after adjustment for postpartum week. Ca and IP concentrations did not differ between groups. Postpartum week was negatively associated with all minerals (all p < 0.001). Maternal age was positively associated with IP, while parity 2 was associated with lower Ca than parity 1. These findings identify postpartum week as a major source of variation in DHM mineral composition and may inform future approaches to DHM compositional assessment and nutritional management of preterm infants.