Looking at risk factors for tree nut sensitization

Tree nut allergies can be dangerous, causing anaphylaxis and even death. There have been few studies that really examined what early-life risk factors can help predict these allergies, and how prevalent they really are—until now.

A new study, published in Clinical and Experimental Allergy, examined the prevalence of tree nut allergies, and what types of allergic reactions were most common at different stages of life. Symptoms of tree nut allergies were assessed at age 12, 16, and 24 years, and immunoglobulin E (IgE) sensitization was tested at 24 years of age. Nuts included in the study were hazelnut, walnut, pecan, cashew, pistachio, Brazil nut, and almond.¹

Hazelnuts were found to be most common tree nut allergy in people who developed sensitization, 20.6% of the study group, but only 7.3% experienced clinical symptoms with this allergy. Even less—6.1%—were sensitized and developed symptoms to hazelnuts.

Most of the study participants were allergic to all types of tree nuts, but hazelnut-only allergies were the second most common phenotype.

In addition to a range of ages and types of nuts, the study also investigated ranges of symptoms and severity of allergic reactions. Potential risk factors examined in the assessment included eczema, asthma, inherited allergy, gender, and the presence of other food.

The study found that 21.2% of study participants were sensitized to tree nuts, and 9.8% of participants experienced allergy symptoms. Most of the people who were sensitized to tree nuts—63%—had no symptoms at all.

“We were surprised that the majority of the tree nut sensitized individuals in our cohort did not report any symptoms at all. We had expected most of the sensitized individuals to at least report mild oral allergy syndrome symptoms, related to cross-reactions to birch pollen. This is important as this implies that extract based IgE-testing for tree nuts without a specific clinical suspicion should not be performed as it may lead to unnecessary avoidance of tree nuts,” said study co-author Jessica Bager, MD, of the Karolinska Institutet in Stockholm, Sweden.

Some trends were identified in the study group, especially among participants who had egg allergies, eczema, or asthma at preschool age. These individuals were at a higher risk of developing future tree nuts allergies, according to the report. Later in life—in the group assessed at age 24 years—tree nut allergies were more common in people who currently had eczema or asthma.

In regard to how much exposure to tree nuts was required to cause a reaction, the study group found that whole nut extract allergies were more common in the groups who were sensitized to tree nuts but developed no symptoms. On the other hand, people in the study group who were sensitized to tree nut storage proteins—molecules that are not inactivated by heating or digestion—and not just nut extracts were most likely to experience tree nut allergy symptoms.

“Because our study reveals that most extract‐based tree nut‐sensitized individuals do not have tree nut allergy, our conclusion is that extract based IgE-testing for tree nuts without a specific clinical suspicion should not be performed,”Bager said.“Also, we confirmed that testing for specific allergen molecules is a more reliable method to find clinically relevant allergy, rather than extract based IgE-testing.”

Overall, the study concluded that most adults with allergies to tree nut extracts were asymptomatic, and that immune-mediated allergy to tree nut proteins were more often linked to symptomatic allergic reactions. Participants who had other allergic-type presentations in childhood—including eczema, asthma, and egg allergies—were more likely to develop tree nut allergies as they aged.

“We found that tree nut whole extract sensitization is common but usually asymptomatic [and] that storage protein sensitization is a more reliable indicator of tree nut symptoms. Tree nut allergy is associated with early onset, persistent and severe atopic disease,” Bager said. “Our findings also suggest that early atopic manifestations are associated with later tree nut storage protein sensitization.”

Bager said she hopes the study will help clinicians tailor both testing and food avoidance education based on this new risk information.

“We hope that less patients undergo extract based IgE-testing without clinical suspicion,” she explained. “On the same note we hope that less asymptomatic patients avoid tree nuts based only on sensitization.

Reference

1. Bager J, Tedner S, Andersson N, et al. Prevalence and early‐life risk factors for tree nut sensitization and allergy in young adults. Clinical & Experimental Allergy. August 6, 2021. Epub ahead of print. doi:10.1111/cea.13994