Adult-onset Food Allergies Are More Common Than Once Thought

Food allergies are often associated with childhood: peanut-free classrooms, dairy-free treats at parties, and friends avoiding red dye, leaving you with their Halloween candy.

While childhood food allergies are more frequently studied, new findings from the American College of Allergy, Asthma and Immunology (ACAAI) annual meeting reveal that 45% of U.S. adults with food allergies developed at least one during adulthood.

Arriving Fashionably Late

A 2015 study by a Chicago research team revealed that over 15% of adult food allergy patients at Northwestern Medicine had at least one allergy that developed in adulthood. This initial study, though limited to a small Chicago sample, was expanded in a new national survey of over 50,000 adults, providing broader insights into the prevalence of adult-onset food allergies across the U.S.

The prevalence of adult food allergies has surged beyond expectations. A 2004 study estimated 2.5% of U.S. adults had shellfish allergies, but the 2017 study found this number rose to 3.6%. Similarly, tree nut allergies, previously estimated at 0.5% in 2008, now affect 1.8% of adults, marking a 260% increase. This means more adults are avoiding treats like Nutella and almond butter.

"Adult-onset allergies are particularly intriguing to study because they likely involve losing immune tolerance to foods that adults have previously consumed without issues," explains co-author Christopher Warren, a preventive medicine doctoral candidate at the University of Southern California, via email. "This differs from childhood food allergies, where the immune system fails to develop tolerance initially. These may represent two distinct biological mechanisms."

What's Going On?

Why do adults lose immunity to certain foods? Demographic trends from the study offer a clue. Certain groups are more prone to specific adult-onset food allergies. For example, Hispanic adults are over twice as likely to develop peanut allergies compared to whites, while Asians face a higher risk of shellfish allergies than whites.

"Several intriguing hypotheses are being explored to explain this phenomenon," says Warren. "For instance, cultural differences in preparing allergenic foods might influence allergy rates to those foods."

Warren notes that roasting peanuts with sugar (via the Maillard reaction) produces advanced glycation end products (AGEs), which increase allergenicity. In contrast, boiling reduces protein allergenicity. This may explain lower peanut allergy rates in Asia, where peanuts are boiled or fried, compared to the Americas, where dry roasting is common. Similarly, shellfish allergies are prevalent among Asian-American participants, aligning with studies in Asia showing shellfish as the most common allergy in older children and adults.

Diet may not be the sole factor influencing why specific populations develop allergies to certain foods more frequently.

"Recent findings from the HealthNuts cohort in Australia indicate that the Asian environment might offer protection against food allergies," Warren explains. "Asian children born in Australia face a higher risk of food allergies compared to those born in Asia who later move to Australia, likely due to differences in diet, bacterial exposure, and UV environments."

Warren and his team aim to explore food allergy prevalence differences in the U.S., examining whether similar patterns exist among migrants compared to those born in the country.