French scientists claim to have added an important piece to the ongoing debate over whether breastfeeding protects children from asthma. Published in the January 29, 2008 issue of Nature Medicine, the researchers found that breastfeeding protects mice from developing asthma. When the mouse mother is exposed to an allergen, like pollen or dust, her milk passes the allergen to her baby where it acts as a stimulus for preventing future allergies. This may explain why some children are more prone to developing asthma than others.

The prevalence of asthma has increased significantly in recent years. Asthma is a chronic disease characterized by airway obstruction. Asthma occurs when T helper type 2 cells fail to respond to environmental allergens in the air. It is believed that exposure to environmental allergens during infancy is crucial to the development of asthma, but epidemiological studies on the relationship between breastfeeding and allergic disease has produced conflicting results.

The French researchers exposed lactating mice to airborne dust containing ovalbumin, a well-known asthma allergen that is found in egg whites. Mice that were breastfed by their mothers appeared to be less susceptible to developing asthma-like symptoms such as wheezing, than were those not breastfed. The authors have suggested that a component in breastmilk—transforming growth factor beta (TGF-ß) is responsible for the asthma protection.

“Breastfeeding induced tolerance may rely on both the chronic administration of an allergen (tobacco smoke, pollen, or mites) at a low dose, a setting known to promote tolerance induction, and the presence of milk-borne TGF beta,” said the researchers.

“This study may pave the way for the design of new strategies to prevent the development of allergic disease,” the scientists added.

If these results can be replicated using human subjects, it may help to explain why allergen avoidance in early life does not prevent allergic disease in later life. The researchers cautioned that this study did not measure levels of allergens in breastmilk. And no consideration was given to the mother’s exposure to airborne allergens when they were breastfeeding.

Scientists from a wide range of biomedical fields have used the mouse model for research because of its close genetic and physiological similarities to humans as well as the ease with which its genes can be manipulated and analyzed, so extrapolating observations in mice to men is not as much of a stretch as one might think.

Although much remains to be learned about how breastfeeding affects the development of allergic disease, there is general consensus that exclusively breastfed for the first six months of life is one of the best strategies for ensuring optimal health.