A new study from McMaster involving 2.8 million children around the world has revealed the most important early-life factors that influence whether a child becomes allergic to food.
The study, one of the largest of its kind to examine food allergies, furthers our understanding of how allergies develop, concluding that a combination of genetic, environmental, microbial and social factors influence allergies, rather than a single cause.
Researchers carried out a systematic review and meta-analysis of 190 studies on childhood food allergy, including those that confirmed allergy using gold-standard food challenge testing. About 5 per cent of children develop a food allergy by age six, found the study, published in JAMA Pediatrics on Feb. 9.
“Our study highlights that genetics alone cannot fully explain food allergy trends, pointing to interactions — or a ‘perfect storm’ — between genes, skin health, the microbiome, and environmental exposures,” says senior author Derek Chu, an assistant professor with McMaster’s departments of Medicine and Health Research Methods, Evidence and Impact.
The study systematically examined more than 340 factors that may influence allergy. Some of the identified early-life factors that raise the risk of food allergies are:
- Infants who experience eczema in the first year of life are three to four times more likely to develop a food allergy. Wheezing or nasal allergies are also linked to higher risk.
- Children with allergic parents or siblings were more likely to develop a food allergy, especially when both parents had allergies.
- Waiting too long to introduce allergenic foods such as peanut, nuts, eggs, or other common allergens can increase the chance of developing a food allergy. Researchers found babies who try peanuts after 12 months are more than twice as likely to become allergic to the legume.
- Another significant factor involves the use of antibiotics. The study highlights how antibiotic use in the first month of life can lead to a higher risk of food allergy. Antibiotics taken later in infancy and during pregnancy can lead to an increased risk, but to a lesser degree.
The findings help identify which infants are most at risk and could benefit most from early prevention strategies. The study also revealed early-life factors that were not associated a higher risk of allergies to food for children, including low birthweight, post-term birth, partial breastfeeding, material diet and stress during pregnancy.
“This study has broadened our understanding of food allergies. Future studies should measure and adjust for the same key factors, include more diverse populations, and use food challenge testing more often. New randomized clinical trials and updated guidelines are urgently needed to move our findings into action,” Chu says.
The research was funded by the Canadian Institutes of Health Research and the AAAAI/ACAAI Joint Task Force on Allergy Practice Parameters.