Most people see the beauty of nature in pristine white sand beaches, the serenity of the forest, the first crocus buds popping out of the ground, etc. For me, (a self-proclaimed science nerd) there is nothing more beautiful about nature than a complex biological mechanism that imparts health.
Case in point: breast milk.
We know that breastfeeding is healthy. Beyond the nutrient composition that makes breast milk good food for babies, what else is in breast milk that makes it the liquid gold some moms claim it to be? In particular, what about the claims that breast milk protects against allergies?
An excellent 2010 review in Mucosal Immunology by Verhasselt takes an in-depth look at the mechanisms by which components in breast milk interact with an infant’s immune system. It seems that the route by which breast milk influences allergies all begins in the gut.
Verhasselt begins with the concept of oral tolerance:
Janeway’s Immunobiology defines oral tolerance as, “ The suppression of specific systemic immune responses to an antigen by the prior administration of the same antigen by the oral (enteric) route.”
In plain English this means that by eating and drinking different foods you get used to the antigens (usually proteins that may elicit an antibody response) they contain. As you come to “tolerate” them, your immune system will not produce an inflammatory/allergic response in future encounters with the same antigen.
Achieving oral tolerance to a wide range of antigens is important, so that individuals do not suffer from food allergies.
Breast milk helps achieve oral tolerance in several ways:
First, breastfeeding allows for regular exposure to very small amounts of antigens. Any potential antigens ingested by the mother will be found in her breast milk. This may include common allergens like proteins from cow’s milk, eggs, peanuts, wheat, and even airborne allergens that the mother may be exposed to. These small amounts seems to be an appropriate dose for helping to confer oral tolerance.
Next, the form of the antigens present in breast milk are more easily tolerated by the infant. The processing that a dietary antigen goes through in the mother’s digestive system before it ever reaches her circulation or enters breast milk seems to help confer toleragenic (more easily tolerable) properties when ingested by the infant in this form.
Further, breast milk usually contains high levels of secretory IgA (s-IgA), a class of antibodies that is present in mucosal secretions and is the predominant class of antibodies found in the gut. S-IgA is able to trap food antigens, and while the mechanism is not fully worked out yet, seems to be important in conferring antigen-specific oral tolerance.
In newborns, there is a certain amount of gut permeability—meaning that there are gaps between the epithelial cells that line the intestines. As the gut matures, these gaps close. Increased permeability seems to be associated with the development of allergies. Colostrum (early breast milk) and more mature breast milk contain gut epithelial growth factors which promote gut closure, protecting against any antigens sneaking past the gut barrier.
In addition, breast milk contains a compound called transforming growth factor- β (TGF- β). This is a cytokine (cell-signaling molecule) involved in regulatory T-cell induction which further promotes oral tolerance.
Finally, the bugs. Much recent research suggests that the microbial composition of the gut impacts the immune system. At birth, the gut of the newborn is sterile, but then quickly becomes colonized by microbes. Some microbes are beneficial and other pathogenic. Of the beneficial bugs, some are more helpful than others. For example, Bifidobacterium and Lactobacillus strains of bacteria have been shown to be most beneficial in allergy prevention. Breast milk contains various nutrients (like glycoproteins and oligosaccharides) that promote the growth of these beneficial strains of bacteria.
So, there are several components in breast milk and mechanisms by which this “liquid gold” does seem to contribute to a lower incidence of allergies. These elaborate mechanisms do make me marvel at the beauty of this nature-provided prevention strategy.
Does this mean I should blame my allergies on my mother’s decision not to breastfeed?
Of course not! There are many other factors that figure into the allergy equation—notably genetics, and other environmental exposures.
Does this provide possible avenues for future allergy prevention?
Possibly. It seems to me that if a breastfeeding mother makes a point to eat a variety of foods during lactation—including possible allergens, it may help to promote oral tolerance in her child. Certainly, further research into this strategy as an effective approach is needed.
However, this is pretty interesting research in that seems to challenge the classic advice to parents to avoid giving their children any common allergens in the first year of life.
Murphy, K. (2012). Janeway’s Immunobiology (8th ed.) New York, NY: Garland Science, Taylor & Francis Group, LLC.
Verhasselt, V. (2010). Oral tolerance in neonates: from basics to potential prevention of allergic disease. Mucosal Immunology; 3(4):326-33. doi: 10.1038/mi.2010.25.