Breast Milk and Breastfeeding

Milk is abundant at our local grocery store in the form of dairy products and infant formulas. This ubiquity of homogenized milk in our modern environment has the potential for the general public, and even researchers, to think of milk unidimensionally. Milk is not just food, however, but is also medicine and signal. Hundreds, possibly thousands, of other milk “bioactives” provide immunity and physiological regulation for the infant. Importantly, milk is not uniform across mothers or within an individual mother across time. Maternal health, nutrition, culture, reproductive history, early-life conditions, and genes all contribute to differences in milk composition. Less understood are the consequences of that variation for infant development and fitness outcomes. Here I will present emerging research that addresses the magnitude, sources, and consequences of inter-individual variation of bioactive constituents in mother's milk. A better understanding of variation in milk composition, especially for milk constituents linked to infant cognition, neurodevelopment, behavior, and metabolism, enhances an evolutionary biological perspective of parent-offspring dynamics. Moreover, biological and social scientific research on this topic can be directly translated into more personalized clinical recommendations and health optimization for mothers and their infants. Identifying the composition and function of milk informs the manufacture of more representative infant formulas, the importance of institutional support, and the necessity for greater advocacy for mothers.