Longitudinal changes in the mineral content of human milk.

Thirty-eight lactating women, from 1 to 31 months postpartum, provided monthly milk samples for determination of calcium, magnesium, manganese, copper, iron, and zinc. Subjects remained in the study an average of 4 consecutive months, with a maximum participation of 9 months. Subject variation accounted for the majority of variance in the raw data. After statistically controlling subject effect, copper, iron, and zinc levels were shown to be significantly related to duration of lactation. Prediction equations for these three minerals were developed, making it possible to calculate, on an individual basis, the copper, iron, and zinc levels of milk to be produced in future months. Data were also collected to determine possible correlations between breast milk mineral levels and the maternal dietary intake, serum levels, or hair concentration of these same minerals. No significant correlation was found between the milk mineral content and any of the three parameters under study.