A large number of biologically active components have been found in human milk (HM), and in both human and animal models, studies have provided some evidence suggesting that HM composition can be altered by maternal exposures, subsequently influencing health outcomes for the breastfed child. Evidence varies from the research studies on whether breastfeeding protects the offspring from noncommunicable diseases, including those associated with immunological dysfunction. It has been hypothesized that the conflicting evidence results from HM composition variations, which contain many immune active molecules, oligosaccharides, lactoferrin, and lysozyme in differing concentrations, along with a diverse microbiome. Determining the components that influence infant health outcomes in terms of both short- and long-term sequelae is complicated by a lack of understanding of the environmental factors that modify HM constituents and thereby offspring outcomes. Variations in HM immune and microbial composition (and the differing infantile responses) may in part explain the controversies that are evidenced in studies that aim to evaluate the prevalence of allergy by prolonged and exclusive breastfeeding. HM is a "mixture" of immune active factors, oligosaccharides, and microbes, which all may influence early immunological outcomes. This comprehensive review provides an in-depth overview of existing evidence on the studied relationships between maternal exposures, HM composition, vaccine responses, and immunological outcomes.
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Declaration of interest. D.M. has received consultancy payment from Dairy Goat Co-Operative (NZ) Ltd. and has given paid lectures for Merck Sharp and Dohme (MSD). D.T.G. received an unrestricted research grant from Medela AG and has received travel funding and support for lectures. J.O.W. has received research grant income from Danone in relation to studies of the value of prebiotics in allergy prevention, and Airsonette to evaluate temperature-controlled laminar airflow for asthma; he is also on a Danone, Union Chimique Belge (UCB) and Airsonette scientific advisory board and has given paid lectures for the companies. J.O.W. is supported by the National Institute for Health Research Collaboration for Leadership in Applied Health Research and Care (NIHR CLAHRC) for North West London and is its Early Years theme lead. The views expressed in this paper are those of the authors and not the NIHR or Department of Health.
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- breast milk
- human milk
- immune active molecules
- immunological outcomes
- vaccine response