Since the beginning of Homo sapiens as a species, breastfeeding has been the main feeding practice for newborns. The earliest documented cases of neonatal breastfeeding date as far back as 2000 BC, and the importance of this practice has been well understood for centuries as a primary source of nutrition for infants. Alternative feeding practices have an equally long history, with evidence of animal milk found in vessels buried with newborn infants also dating back to 2000 BC. When various forms of milk were first analyzed for their health benefits during the 18th century, scientists realized the potential health benefits of human milk and tried to replicate its components in a synthesized formula. Thus birthed the invention of formula milk, which represented a new chapter in infant feeding that has since become a common choice of supplementation or replacement for breastfeeding, particularly for mothers who are unable to breastfeed due to health, cultural, or societal reasons.
The health benefits of breastfeeding extend beyond nourishment, and is crucial to the development of a healthy immune system. To many, the nutrients found in breast milk and formula are one and the same, a notion that is, in fact, far from the truth. Apart from the vitamins and macromolecules gained from breast milk, the immunological factors and healthy microbes that are transferred help reduce the risk of numerous diseases such as asthma, obesity, type 1 diabetes, as well as respiratory and gastrointestinal disorders. Dietary guidelines provided globally by the World Health Organization (WHO) typically recommend feeding for 6 consecutive months with only breast milk, followed by an additional 1.5 years of breast milk alongside the gradual introduction of age-appropriate food.
The first two years after birth also encompass a physiologically vulnerable and malleable period that can be significantly affected by diet. Breast milk is packed with rich bioactive nutrients, bacteria, and immune cells and their secreted molecules, which can safely promote infant gut health and immune system development.
While still in the womb, a fetus’ immune system is under development, and the first B and T cells begin to form as early as the second or third month of pregnancy. However, since the mother’s womb is sterile, these immune cells have never been tested against any environmental threat and remain inactivated. In addition to these inexperienced cells, the fetus also receives antibodies from the mother through the placenta. These antibodies are referred to as immunoglobulin Gs (IgGs), which are a class of antibodies commonly found in circulation and are the only ones capable of passing through the placental barrier. Upon birth, the infant is exposed to an entirely new environment, and the passive immune protection provided by the mother’s IgGs will stick around until the infant’s immune system activates and can take control. This passive immune protection can protect the infant for a short period following birth, but is one class of antibodies enough?
The short answer: sort of, but the more classes of antibodies present, the broader the scope of protection and the more this passive immune system can “cover its bases”. Breast milk includes another important antibody, IgA, a common antibody type found near mucosal tissues. Other classes of antibodies can also be present, such as IgM and IgG, depending on the mother’s environment and history of infection. Additionally, breast milk contains other immunomodulatory factors, such as nucleotides, amino acids, polyunsaturated fatty acids, soluble immune effector proteins, antibacterial proteins/peptides, and even immune cells, such as macrophages and neutrophils. All these modulators are crucial for immunity at birth, as the infant’s immune system, at this stage, is highly limited. The mother’s immune cells and effector molecules not only help protect the baby from foreign particles but also help to form tolerance to harmless food components.
The microbiota, a diverse community of bacteria that covers the body, inside and out, is largely implicated in human health and interacts with the host immune system to protect against invading pathogens. With regards to microbiota, a fetus’ gut is a blank slate, upon which different microorganisms will colonize based on the circumstances of birth. This first introduction of an infant’s gut to healthy microbiota is typically in the vaginal canal during birth; if birthed through a different method, then the first time is often when fed breast milk. Like immune components, breast milk is packed with beneficial bacteria that can promote healthy infant gut colonization and maturation. Studies have shown that two major groups of bacteria in breast milk, Bifidobacteria and Lactobacilli, can metabolize oligosaccharides present in the milk to help promote intestinal barrier integrity and inhibit the settlement of pathogenic bacterial species. Early gut microbial colonizers will eventually occupy their niche in the gut; through competition for nutrients and space, they limit further colonization by other microbes, eventually reaching homeostasis to help maintain a balance between the immune system and the external gut environment. Commensal bacteria are known to play key roles in stimulating sub-populations of immune cells, such as promoting the development of T cells with anti-inflammatory functions, and IgA-producing B cells, that help integrate the immune system.
Given the rich source of immune cells and immunomodulatory components in breast milk, simply breastfeeding for the first 6 to 24 months of an infant’s life can greatly reduce the risk of hospitalization due to severe infections; inflammation-related symptoms such as diarrhea, acute otitis media, and asthma; and other health concerns such as obesity.
Despite the benefits that breastfeeding provides over other methods, formula feeding is still a popular choice among new parents. The advantage of anyone being able to feed your child, along with less frequent feeding times, increased satiation rates, and excess amounts of nutrients, make it out to be a very easy and reliable feeding method during what is, undeniably, a very stressful time for new parents. However, while formula milk has provided an accessible option for mothers who are unable or choose not to breastfeed – for example due to biological issues related to lactation, the social norms of their culture, or economic issues related to the lack of paid family leave – breastfeeding remains the best option to support both nutritional and developmental needs of growing infants.
Rafeed Khan
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