Dynamics of the Main Immunologically and Nutritionally Available Proteins of Human Milk during Lactation

Microparticle-enhanced nephelometric immunoassays were specifically developed for the quantification ofα -lactalbumin, β -casein, serum albumin, lactoferrin, and lysozyme in human milk. These components, immunoglobulin A and total proteins were assayed in 780 samples collected from 79 mothers during the first 12 weeks of lactation. The data obtained provide a precise description of the dynamics of human milk evolution over time and allow to depict six periods. In the early post-partum period (days 1–4), colostrum contains principally immunological components. The relative concentrations of immunologically and nutritionally available proteins are reversed during the following short transition period (days 5–8). Milk then secreted (days 9–18 and 19–28) appears to have principally a nutritious function. During the two following periods (days 28–49 and 50–84), milk appears well balanced in its nutritional and immunological components, supplying breast-fed infants with appropriate food intake for growth and development and passively protecting them by reincreasing concentrations of immunological components.