Researchers reviewed 146 previous studies that examined when babies were given foods that often trigger reactions, as well as their risk of food allergies or autoimmune diseases.
They discovered that the timing of food introduction may affect allergy risk, but they found no similar link for autoimmune disease.
The researchers reported with "moderate certainty" that babies who were given eggs when they were 4 months to 6 months old had a lower egg allergy risk. And children given peanuts between 4 months and 11 months of age had a lower peanut allergy risk than those who were older.
The study, published Sept. 20 in the Journal of the American Medical Association, said early introduction could head off 24 cases of egg allergy per 1,000 people and 18 cases of peanut allergy per 1,000 people.
The evidence was not as strong for early introduction of fish.
The researchers found low certainty that giving a baby fish before 6 months to 12 months of age would reduce the risk of nasal allergies or hay fever (allergic rhinitis). And they reported very low certainty that doing so before 6 months to 9 months of age would reduce their risk for food allergies.
The evidence surrounding gluten was clearer: Timing does not appear to affect the likelihood of celiac disease, an immune disorder that causes bowel damage.
Guidelines on food introduction have been relaxed in recent years. Parents are no longer advised to delay offering foods like eggs and peanuts to their children for fear of triggering allergies, the study authors said.
More study would be needed before revising current guidelines, the authors said.
Dr. Matthew Greenhawt is an allergy specialist at Children's Hospital Colorado in Aurora, who wrote an editorial accompanying the study.
"Delay of introduction of these foods may be associated with some degree of potential harm, and early introduction of selected foods appears to have a well-defined benefit," Greenhawt wrote.
"These important points should resonate with allergy specialists, primary care physicians, and other health care professionals who care for infants, as well as obstetricians caring for pregnant mothers, all of whom are important stakeholders in effectively conveying the message that guidance to delay allergen introduction is outdated," he said.
The American College of Allergy, Asthma & Immunology provides more information on food allergies.
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