The effect of prolonged and exclusive breastfeeding on the risk of allergy and asthma has been the subject of debate for decades. While some studies report a beneficial effect on the risk of atopic dermatitis, the evidence on asthma, hay fever, and food allergies remain mixed.

Michael Kramer and colleagues conducted a cluster randomized trial that included 31 maternity hospitals and clinics in Belarus. A total of 13,889 mother-infant pairs were followed for a period of 6.5 years. Hospitals and clinics were randomly assigned to an experimental or control group. Breastfeeding promotion intervention strategies modeled after the WHO/UNICEF baby friendly hospital initiative were implemented at the experimental sites; control sites continued the practices and policies in place at the time of randomization.

The experimental intervention led to a substantial difference in the duration of any breastfeeding at 3 months (72.7% versus 60%), 6 months (49.8% versus 36.1%), 9 months (36.1% versus 24.4%), and 12 months (19.7% versus 11.4%). In addition, the prevalence of exclusive breastfeeding was sevenfold higher in the experimental group at 3 months (43.3% versus 6.4%) although low in both groups at 6 months (7.9% versus 0.6%).

Despite the increase in breastfeeding rates (any and exclusive), the investigators found no reduction in the risk of asthma, other allergic diseases, and positive skin prick tests at age 6.5 years. The reliability of skin testing is influenced by many variables, including the technique of the tester, the device used for administration, the potency of the extracts, the spacing between the antigens, the position of the arm, and even the time of day. But even after excluding data from 6 sites due to suspiciously high rates of positive skin prick tests, the relative odds of positive skin prick tests were twofold to threefold higher in the experimental group than in the control group.

The investigators concluded that given the increase in atopic disease (asthma, hay fever, atopic dermatitis) in recent years simultaneous with increases in breastfeeding rates, it appears breastfeeding does not have a protective effect at the population level. Given the complexity of atopic disease and its strong genetic component, it has long been suggested that breastfeeding more likely delays the onset of symptoms and causes the symptoms, when they do appear, to be less severe. This can be still be significant if you are a parent of an infant or young child with atopic disease.

It’s also important for parents to understand that the results of this one study don’t diminish the importance of breastfeeding for maternal and infant health.