Pregnancy and child

Breast milk ‘protects against allergies’

Breastfeeding could “help babies avoid asthma caused by allergies in later life”, reported The Daily Telegraph . When the mother is exposed to an allergen, such as pollen or dust, “her milk passes these allergens [to her child], which wards off future allergies”, the newspaper said.

The newspaper report is based on a French study that found that exposing breastfeeding mice to an airborne allergen helped prevent allergic asthma in their offspring. As this is an animal study, direct application of these findings to human health is a step too far. More research will be needed before these findings translate into treatment or prevention strategies for human children.

Where did the story come from?

Valérie Verhasselt and colleagues from L’Institut National de la Santé et de la Recherche Médicale and other academic institutes in France carried out this research. The study was funded by Le Fondation Pour la Recherche Médicale and by a grant from the European Union (DC-THERA) It was published in the peer-reviewed medical journal: Nature Medicine .

What kind of scientific study was this?

This was a laboratory experiment in mice and their offspring. The researchers were interested in the effect on offspring mice if the breastfeeding mother mice was exposed to a substance in the air that causes an allergic reaction (an allergen).

The researchers exposed one group of breastfeeding mice to an airborne allergen (ovalbumin) while a second group was not exposed. When the offspring of the two groups had reached adulthood, the researchers exposed them to the same airborne allergen and carried out various tests to compare what effects the allergen had on the lungs and on their immune responses. They compared the number of white blood cells in the lungs, the production of mucus in the airways and other immune responses.

The researchers then tried to work out how the protection was being transferred to the offspring. First, they measured whether there was any allergen present in the breast milk. They then used mother mice that were genetically modified so that parts of their immune system did not work properly. This allowed the researchers to establish what exactly was passing through the milk to protect the offspring, to work out whether it was the actual allergen or a by-product of the mother’s immune response to it.

Previous studies had suggested that a particular chemical – transformational growth factor (TGF-β) – needed to be present in the immune system in order to protect it against an allergic reaction. The researchers investigated whether this was the case by injecting TGF-β into breastfeeding mice and then compared the protection in adult offspring with that in offspring breastfed by mothers with a TGF-β deficiency.

What were the results of the study?

Mice from mothers who were exposed to the allergen were less likely to have an immune response to the same allergen when they were exposed as adults. The researchers confirmed that this protection was conferred by the allergen (ovalbumin) passing through breastmilk to the offspring.

They also found that the mechanism that protected the offpring from an allergic response was achieved by the suppression of a particular element of the immune response (CD4+ T cells). This suppression required the action of the chemical, transformational growth factor (TGF-β). 

What interpretations did the researchers draw from these results?

The study found that “antigen-specific” protection was transferred from breastfeeding females to their offspring through breast milk. Using the findings from other studies, the researchers say that the airborne allergen most likely ends up in breast milk by transfer through the gut. The researchers conclude that their findings give new “insights into the mechanisms underlying tolerance induction in neonates”.

What does the NHS Knowledge Service make of this study?

This laboratory study uses well known methods to assess the mechanisms by which protection from lung disease is conferred on mice through breastfeeding. The findings will be interesting to the scientific community as they shed light on complex processes involved in the immune system. The researchers acknowledge that their study did not assess the effects on the offspring when the mothers have an allergic reaction to the allergen. Exposure in this study was to one airborne allergen only and the findings should not be taken to represent exposure to all other allergens.

Although The Daily Telegraph suggests that breast fed babies have fewer and less serious allergies than formula-fed babies, the evidence is not clear-cut. The newspaper goes on to quote the researchers who themselves say that “epidemiological studies on the relationship between breastfeeding and the development of allergic diseases have yielded conflicting results”.

These are interesting findings, but until more work is done to follow up their relevance to the situation in humans, prevention and treatments based on this technology are someway off.

Sir Muir Gray adds...

Breast is best!

NHS Attribution