Reference Values for Minerals in Human Milk: the Mothers, Infants and Lactation Quality (MILQ) Study

This fifth article in the series presenting reference values for nutrients in human milk describes minerals. The Mothers, Infants and Lactation Quality (MILQ) and Early-MILQ studies collected human milk samples throughout the first 8.5 mo of lactation in 1242 well-nourished women in Bangladesh, Brazil, Denmark, and The Gambia. All minerals were measured by inductively coupled plasma-mass spectrometry. Although pooled MILQ medians from 1 to 6 mo are within ∼10% of the concentration used by the Institute of Medicine (IOM) for magnesium, potassium, calcium, and copper, they are ∼50% of the IOM value for zinc and selenium, and ∼75% of the IOM value for sodium and iron. For zinc, sodium, and iron, the discrepancy can be explained by the IOM's use of values from early lactation (<3 mo) when the milk nutrient concentrations are higher; in contrast, for potassium the IOM benchmark concentration is consistent with later lactation (6 mo) in MILQ. Pooled median MILQ phosphorus from 1 to 6 mo is 120% of the concentration selected by the IOM. Milk iodine concentrations in MILQ varied among sites, reflecting the differing national policies for salt iodization. Total daily median mineral intakes from 1 to 6 mo were 49%-55% of IOM adequate intakes (AIs) for zinc and selenium, 74%-90% of AIs for sodium, iron, and magnesium, and 110%-125% of AIs for copper, potassium, calcium, and phosphorus. For zinc, sodium, iron, and potassium, differences can be explained by the reference time frame during lactation. The MILQ study mineral concentrations are provided as percentile curves to enable comparison and interpretation. Importantly, the MILQ data show marked changes in milk mineral concentrations during the first 6 mo of lactation, an observation often missed because of the absence of data representing a spectrum of time postpartum in previously published data.