Lysozyme, lactoferrin, and secretory immunoglobulin A content in breast milk: influence of duration of lactation, nutrition status, prolactin status, and parity of mother.

Milk lactoferrin (LF), lysozyme (LZ), and secretory IgA (sIgA) were measured cross-sectionally in 127 Zaïrean mothers, lactating greater than or equal to 18 mo. The 54 urban mothers were of marginal nutrition status [body mass index (BMI) 22.6 +/- 2.6 kg/m2 and albumin 33.1 +/- 4.5 g/L]. The neighboring rural mothers were of significantly (P less than 0.001) poorer nutrition status (BMI 20.5 +/- 2.2 kg/m2 and albumin 27.7 +/- 5.4 g/L). In both urban and rural mothers, as lactation progressed LF decreased by 33% and 55% whereas sIgA remained unchanged and LZ steadily increased. There was more LZ and sIgA in rural milk, contrasting with the poorer maternal nutrition. As calculated from individual milk yields, the urban infants were fed daily with twice as much LF and sIgA but with similar amounts of LZ as were the rural infants. In the early stage of lactation, the milk of both groups of Zaïrean mothers contains more sIgA than that of a group of west European (Belgian) mothers (n = 20), but the LF and LZ contents were rather similar.