Multiple nut allergies more common than previously thought

August 5, 2020

Children who are allergic to 1 type of nut are often allergic to multiple nuts or seeds, according to a recent report.

Children who are allergic to 1 type of nut allergy are more likely to have another, according to a recent report.

The study, published in the Journal of Allergy and Clinical Immunology, evaluated coexistent nut and seed allergies in children across Europe, tracking prevalence and similarities between types of allergens.1 Researchers found that, overall, there were more coexistent nut and sesame seed allergies than previously reported.

Peanut and tree nuts are the most common food allergen, increasing by 2.1% in children in the United States over the past 30 years. Across Europe, the team found geographical differences in tree nut allergy prevalence based on pollen sensitization.

“Sensitization to nuts is affected by pollen sensitization because of cross-reactive allergens, and only a proportion of children sensitized to nuts will truly be allergic,” the report notes.

Peanut and tree nut allergies often cause severe, anaphylactic, and sometimes fatal reactions, and sesame seed allergies are also associated with severe reaction, the research team notes. These allergies often start early in life with a single tree nut or peanut allergy, and those children usually develop multiple nut allergies over time. A report from the United Kingdom found that 1 cohort of children had a 23.5-fold increase in multiple nut allergies over roughly a decade. Therefore, having peanut, tree nut or sesame seed allergies increases the risk of frequent food allergy reactions significantly, and quality of life drops as the number food allergies rise.

According to the report, 20% to 50% of individuals in the study self-reported co-existent peanut and tree nut allergies on a questionnaire at the start of the study. These results may not be accurate, though, the study notes, as individuals may overestimate allergy symptoms and cross-reactivity between peanuts and tree nuts.

Oral food challenges were done on study participants to get a more accurate number of co-existent allergies. Previous estimates of co-existent peanut and tree nut allergies after oral food challenges were around 30%, but more of these studies were limited and done retrospectively. Additionally, in prior reports, 58% to 84% of children with sesame seed allergies also had allergic reactions to peanuts, and about a quarter of children with peanut allergies also had sesame seed allergies.

The goal of the study was to evaluate these past observations against new testing with oral food challenges, examining reactions to peanuts, 9 different tree nuts, and sesame seeds in children with at least 1 proven nut or seed allergy. Children were assessed from different regions in Europe for comparison purposes—London, Geneva, and Valencia.

Children with life-threatening reactions in the past were excluded from the study, and a total of 159 across the 3 regions participated. Twenty-one later dropped out of the study for various reasons, including fear of a serious reaction. A total of 866 oral food challenges were performed on the remaining children, and 60.7% of the children in the study were allergic to more than 1 nut or seed. A single nut allergy was found in about 39% of the study group, and the maximum number of allergies any participant had was to 9 of the nuts or seeds tested.

Peanut allergies were the most common overall at 49%, followed by walnut allergies at 42.6% and cashew allergies at 34.3%. This number could be skewed, the researchers note, as the highest number of participants came from London, where peanut allergies were most prevalent. Cashew and pistachio allergies were most common among the Geneva group, and walnut and pecan allergies were most common in Valencia. If the number of children from each area were equal, the research team suggests that walnuts actually would have been the most common allergen, followed by peanuts and then pecans. Valencia had no cases of sesame seed allergies at all,.

Most children came to the study with their index, or presenting, allergy as the peanut, followed by walnut, hazelnut, and cashew. According to the research team, no children listed pecans as their index allergen. Sesame seeds, Brazil nuts, pistachios, almonds, macadamia, and pine nuts were sometimes, but seldom, listed as index allergens. The latter were among the most often consumed seeds and nuts before the study was conducted, the report notes.

In looking at common threads among children with multiple nut and seed allergies, researchers found that children older than 36 months of age had a higher chance of multiple nut allergies. In Geneva, there was also a connection between other non-nut food allergies and an increased risk of multiple nut allergies. This was not found in other areas. Age, and other conditions like asthma, were not associated with an increased risk of multiple nut allergies, the study notes. Researchers also found that allergies to certain nuts—macadamia, pistachio, and pecan­—were only present in children with 3 or more other nut allergies. Hazelnut and walnut allergies were present in most of the children with 3 or more nut allergies, too, according to the study. Children who could eat cashews, peanuts, walnuts, or pecans before the study were generally allergic to fewer nuts.

There were several other links noted between nuts in children with co-existent allergies, according to the report. Cashew and pistachio allergies were the most highly correlated, followed by walnut and pecan. The relationships varied though, as 97% of children with pistachio allergies were allergic to cashews, but only 83.3% of children allergic to cashews were allergic to pistachios. The case was similar for walnuts and pecans. Again, 97% of children with pecan allergies were allergic to walnuts, but only 75% of children with walnut allergies were allergic to pecans. Additional clusters and correlations are listed within a table in the study.

Oral food challenges can be difficult and stressful to conduct, and some children even dropped out of the study for fear of severe reactions to the food challenges as noted earlier. Overall, there were few severe reactions, but epinephrine was required for a lot of the positive food challenges. Reactions to almonds, macadamia nuts, and walnuts required epinephrine most often. Brazil nuts, sesame, and macadamia had the highest severity of symptoms during the challenges, with sesame seeds producing reactions in the highest number of organ systems in the London cohort.

Overall, the research found that the prevalence of multiple, co-existent nut allergies was about 20% higher than previously reported. Although oral food challenges present a lot of risk, they also allowed the study team to make connections between common allergen relationships. Children were encouraged to begin consuming nuts to which they didn’t develop a reaction during the study, despite the fact that current guidance is for children with 1 nut allergy to avoid consuming any nuts. The study team is working to see if the children in the study group followed this advice, and what their ongoing reactions have been. Ongoing results could be used to reduce the number of diet restrictions for individuals with nut allergies.

Reference

1. Brough H, Caubet J, Mazon A, et al. Defining challenge-proven coexistent nut and sesame seed allergy: a prospective multicenter European study. Journal of Allergy and Clinical Immunology. 2020:145(4):1231-1239. doi:10.1016/j.jaci.2019.09.036