Inorganic constituents of breast milk from vegetarian and nonvegetarian women: relationships with each other and with organic constituents

Abstract

Changes in concentrations of minerals, trace elements, protein, lactose and total lipids during 20 mo of lactation and correlations between levels of these milk constituents were studied in a carefully defined set of 222 milk samples collected from 52 women, one-half of whom were vegetarians. Milk samples from vegetarians and those from nonvegetarians contained similar levels of iron, copper, zinc, sodium, potassium, calcium, magnesium, lactose and fat. Following a brief but sharp initial decrease, levels of protein and iron did not change significantly between mo 2 and 20 of lactation. Levels of zinc, copper, sodium and potassium declined for the first 6 mo of lactation. Levels of lipid, sodium and zinc increased during later months of lactation while that of calcium decreased. Levels of lactose, copper, potassium and magnesium remained unchanged during mo 7-20. Stepwise multiple regression analysis showed positive correlations between levels of three pairs of inorganic constituents during the first 6 mo of lactation: copper and zinc, copper and potassium, and potassium and calcium. During the subsequent 14 mo of lactation, potassium was correlated with copper. The level of iron was positively correlated with that of lipid, while that of calcium was negatively correlated with that of lipid. These relationships, and others reported in the paper, are discussed in relation to current hypotheses of the mechanism of milk secretion and the binding of inorganic to organic milk constituents.