The Prebiotic and Probiotic Properties of Human Milk: Implications for Infant Immune Development and Pediatric Asthma

Abstract

The incidence of pediatric asthma has increased substantially in recent decades, reaching a worldwide prevalence of 14%. This rapid increase may be attributed to the loss of "Old Friend" microbes from the human microbiota resulting in a less diverse and "dysbiotic" gut microbiota, which fails to optimally stimulate immune development during infancy. This hypothesis is supported by observations that the gut microbiota is different in infants who develop asthma later in life compared to those who remain healthy. Thus, early life exposures that influence gut microbiota play a crucial role in asthma development. Breastfeeding is one such exposure; it is generally considered protective against pediatric asthma, although conflicting results have been reported, potentially due to variations in milk composition between individuals and across populations. Human milk oligosaccharides (HMOs) and milk microbiota are two major milk components that influence the infant gut microbiota and hence, development of the immune system. Among their many immunomodulatory functions, HMOs exert a selective pressure within the infant gut microbial niche, preferentially promoting the proliferation of specific bacteria including Bifidobacteria. Milk is also a source of viable bacteria originating from the maternal gut and infant oral cavity. As such, breastmilk has prebiotic and probiotic properties that can modulate two of the main forces controlling the gut microbial community assembly, i.e., dispersal and selection. Here, we review the latest evidence, mechanisms and hypotheses for the synergistic and/or additive effects of milk microbiota and HMOs in protecting against pediatric asthma.

Keywords: asthma; human milk; human milk oligosaccharides; immune development; microbiota; pediatrics; prebiotic; probiotic.

Figure 1

Hypothesized pathways of association between breastfeeding and lung health. Breastfeeding influences infant gut microbiota development and stability during the critical developmental period in early life via two of its main components: human milk oligosaccharides (HMOs) and milk microbiota. HMOs exert a selective pressure within the infant gut microbial niche, preferentially promoting the proliferation of specific bacteria including Bifidobacteria. Milk is also a source of viable bacteria originating from the maternal gut and infant oral cavity. HMO composition is influenced by maternal genetics, geography, and season while microbiota is affected by maternal weight status, mode of breastfeeding and infant sex (Table 1). Variations in HMOs and milk microbiota could modulate the effect of breastfeeding on the infant gut microbiota, which in turn shapes the infant immune system and could ultimately influence lung health and asthma development.