BACKGROUNDOptimal mineral intakes are important for infant growth and development. However, data on mineral compositions of breast milk in Chinese women are scarce, and most were acquired before 1990. The objectives of this study were three-fold: (1) to investigate the mineral compositions of Chinese healthy mothers' breast milk in different lactation stages; (2) to explore correlations among mineral concentrations in breast milk; and (3) to explore the associated factors affecting mineral compositions in breast milk.

METHODSThe inductively coupled plasma mass spectrometry (ICP-MS) was used to analyze mineral concentrations in breast-milk of 444 healthy lactating women from three cities in China. A questionnaire was used to survey socio-demographic characteristics and pregnancy history. Food intakes by lactating women were measured using both food frequency questionnaire and one cycle of 24-hour dietary recall.

RESULTSMineral compositions of breast milk varied in different regions. Concentrations of most minerals were higher in the first one or two months of lactation, and then decreased with time, except for magnesium and iron. Inter-mineral correlations existed among several minerals. The calcium-to-phosphorus ratio was above 2:1 in each lactation stage. Women with caesarean section had higher concentration of iodine in the transitional milk (349.9 µg/kg) compared to women with natural delivery (237.5 µg/kg, P < 0.001). Dietary mineral intakes, supplements, food intake frequencies in the recent 6 months, maternal age and maternal BMI did not show significant correlations with concentrations of milk minerals (all P > 0.05).

CONCLUSIONSMilk minerals decreased with time, and changed most rapidly in the first one or two months of lactation. Caesarean section might affect the iodine level in transitional milk.