Nestlé Nutrition Institute Workshop Series Vol. 94

Lactation and the process of breastfeeding has been integral to the survival and long-term well-being of neonates and infants of most mammalian species. Mothers’ milk has been considered as a complete source of nutrition for the suckling infant from times immemorial, often with many magical healing powers. It is only in the past 2 centuries that significant scientific information has become available about the evolution of the mammary glands and the development of lactation and its impact on the suckling mammalian neonate. Since the observations of Paul Ehrlich over 120 years ago, it is now clear that mammalian breastfeeding is associated with significant reduction in infant mortality, protection against enteric, respiratory, and other mucosal and systemic infections, and protection against the development of allergic disorders. Recent observations have demonstrated that breastfeeding has a profound impact on the development and function of the neonatal immune system, mucosal microbiological homeostasis, and long-term protection against autoimmune and other inflammatory disease states and malignancy. The nutritional and immunobiological benefits attributed to breastfeeding are related to the diverse spectrum of specific cellular and soluble products present in the early colostrum and milk. It is now clear that the immunologic activity in the products of lactation represents the effector functional elements of the common mucosal immune system. The discovery of the secretory IgA (SIgA) immunoglobulin isotype in the milk, followed by the identification of antibacterial, antiviral, and antiparasitic activity in the milk associated with SIgA and demonstration of important elements of cellular immunity in the milk represent crucial milestones in the understanding of lactation as the single most important element of neonatal health in most mammalian species.