Human Milk Composition to 24 Months

Human infants, as altricial mammals, are born with relatively immature central nervous, immune and intestinal systems, requiring high care input, of which lactation is a core evolved adaptation unique as a reproductive strategy as unique to all mammals. Milk is a remarkably complex bio-fluid containing thousands of bioactive molecules acting individually and in synchrony to drive and programme which provides developmental cues through a variety of signalling mechanisms that drive the normal development of each organ system. Recent discoveries in the field of the microbiome, gut-brain axis development and essentiality of human milk provision for normal development have highlighted the critical nature of breastfeeding human milk consumption for normal development over at least the first year of life. Rapid brain development occurs in the early postnatal phase, along with patterning of the gut microbiome and initial maturation of the immature neonatal immune system. Given the evolutionary pressures that drove species-specific milk composition were likely to be based onresulted from enhanced immunity and antimicrobial function, with with nutrition as a relatively recent secondary function, , it is unsurprising that the normal duration of breastfeeding by mothers living in cultures untouched by Western lifestyle is at least 2 years, and beyond until the child reaches immunological maturity. Children's immunity remains incompletely developed until they are over 5 yr, and human milk presumably supports the infant into childhood until they reach immune maturity.