Gut microbiota maturity mediates the protective effect of siblings on food allergy

The mechanisms underlying the protective effect of older siblings on allergic disease remain unclear but may relate to the infant gut microbiota.

We sought to investigate whether having older siblings decreases the risk of IgE-mediated food allergy by accelerating the maturation of the infant gut microbiota.

In a birth cohort assembled using an unselected antenatal sampling frame (n = 1074), fecal samples were collected at 1 month, 6 months, and 1 year, and food allergy status at 1 year was determined by skin prick test and in-hospital food challenge. We used 16S rRNA gene amplicon sequencing to derive amplicon sequence variants. Among a random subcohort (n = 323), microbiota-by-age z scores at each time point were calculated using fecal amplicon sequence variants to represent the gut microbiota maturation over the first year of life.

A greater number of siblings was associated with a higher microbiota-by-age z score at age 1 year (β  = 0.15 per an additional sibling; 95% CI, 0.05-0.24; P = .003), which was in turn associated with decreased odds of food allergy (odds ratio, 0.45; 95% CI, 0.33-0.61; P < .001). Microbiota-by-age z scores mediated 63% of the protective effect of siblings. Analogous associations were not observed at younger ages.

The protective effect of older siblings on the risk of developing IgE-mediated food allergy during infancy is substantially mediated by advanced maturation of the gut microbiota at age 1 year.