Longitudinal changes in the mineral content of human milk

The composition of human milk varies among women and even in an individual, but there is little longitudinal data on the mineral content and changes with the duration of lactation. Mineral content of monthly milk samples provided for up to 9 months from 38 women from 19 to 42 years and from 1 to 31 months postpartum were analyzed. Moisture percentage varied little, but ash levels declined steadily. Zinc and calcium showed the greatest declines followed by iron and copper. Magnesium and manganese did not change. Equations were developed to calculate the concentration of zinc, copper, or calcium in an individual's milk up to 31 months postpartum from a single sample analysis. Dietary intake analysis of 11 subjects indicated that 70% of the women took mineral supplements; iron reached recommended allowances, but calcium, zinc, and magnesium were below. Intake of copper, which has no recommended allowance, tended to be higher than suggested levels. Serum and hair mineral levels showed no significant relationship with the mineral content of milk.