Breast milk can protect babies against food allergies – but only if the mother has consumed the catalyst foods first.
In a mouse-model study published in the Journal of Experimental Medicine, researchers at the Boston Children’s Hospital, US, set out determine whether maternal consumption of allergy-inducing foods such as peanuts and milk resulted in protective antibodies being transferred to babies via breast milk.
The mechanism has been suggested many times before, but results in human studies have been conflicting. A 2001 report in the Journal of the American Medical Association found that peanut protein contained in breast milk was a likely source of “occult exposure” to the allergen, potentially sensitising the infant to an allergenic response the next time peanuts are encountered.
A 2017 study in The Journal of Allergy and Clinical Immunity found (in a small cohort) that the presence of house dust mite allergens in breast milk could sensitise infants to allergic rhinitis and other respiratory illnesses.
And a review published in 2017 in the journal Current Nutrition and Metabolic Care looked at several recent studies and concluded that World Health Organisation guidelines recommending breast feeding “for the prevention of allergies are not supported by the recent study results.”
One of the issues with human studies into the role of breast milk in either boosting or preventing allergies lies in determining the timing of exposure and reaction.
“Whether mothers should eat allergenic foods during pregnancy or avoid them has been controversial,” says Michiko Oyoshi, who led the research.
“Different studies have found different results, in part because it’s hard in human studies to know when mothers and babies first encountered a specific food. But in a mouse model, we can control exposure to food.”
To make their findings, Oyoshi’s team fed pregnant mice allergy-inducing foods. The immune systems of the adult mice produced antibodies – namely, allergen-specific regulatory T immune cells – which were subsequently passed to the infants through breast milk.
The infants were then protected against allergenic reaction to the same foods. They showed no signs of anaphylaxis, nor of other allergy-indicators such as the production of immunoglobulin-E or a type of white blood cell called mast cells.
In further tests, the scientists transferred allergy-specific antibodies from female mice that had been exposed to allergens to those that had not. The unexposed mice transferred the antibodies to their young through breast milk, resulting in protection.
In addition, the same experiments were conducted on specially bred mice that have “humanised” immune systems. The same results were observed, suggesting, the scientists say, that the process might work with human mothers and infants as well.
However, they are quick to sound a note of caution, pending human trials.
“Our study does not suggest that mothers’ peanut eating will guarantee a healthy baby,” says Oyoshi.