How siblings protect babies from food allergies

Published: May 5, 2023

For more than three decades researchers have known that children from larger households are less likely to develop allergic disease and asthma, but the underlying mechanism has remained uncertain. Humans and their gut bacteria evolved together over time. The collection of bacteria that live in the human gut, known as ‘the gut microbiota’, plays a crucial role in keeping us healthy. Researchers from the Barwon Infant Study hypothesised that older siblings speed up the rate at which babies develop their gut microbiota and that this protects the baby from developing food allergy.

Findings from the Barwon Infant Study published in The Journal of Allergy and Clinical Immunology (JACI) provide new evidence regarding the role of gut bacteria in the prevention of food allergy. The team, led by Professor Peter Vuillermin, collected fecal samples over the course of infancy among over 1000 infants and then tested whether the children were allergic to five different foods at 1 year of age. The babies had a skin prick allergy test, and if this was positive, a food challenge. The most common forms of food allergy were egg and peanut. DNA from the fecal samples was used to measure the baby’s gut bacteria. The baby’s chronological age was then used to calculate a gut microbiota maturity score. A formal mediation analysis was then used to investigate the hypothesis that the protective effect of having more siblings on an infant’s risk of food allergy is mediated by accelerated maturation of the gut microbiota.

Babies with older siblings had a substantially more mature gut microbiome by 1 year of age. In turn, a more mature microbiota at 1 year of age was strongly associated with the absence of food allergy. Greater than 60% of protective effect of greater sibling numbers on the baby’s risk of food allergy was mediated by accelerated maturation of the gut microbiota. The effect did not relate to any single type or group of bacteria but rather appeared to relate to the overall composition of a more mature gut microbiota.

The observation that children from larger households are less likely to develop allergic disease formed the basis of the hygiene hypothesis and has been replicated in many studies. The findings for the Barwon Infant Study provide strong evidence that this protective effect is driven by older siblings impacting how rapidly the baby’s gut microbiota mature during late infancy.  

The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.

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