People with nut allergies may really only be sensitive to birch pollen

SOLNA, Spain — Nut allergies have led to food policy changes in schools, airplanes, and workplaces around the country. For some, allergic reactions can be potential fatal. But are all nut allergies created equal? According to a new study, most people diagnosed with a nut allergy may actually only have a sensitivity to birch pollen.

Tree nut allergies are among the most common food allergies in both children and adults. The six tree nut allergies most commonly reported are sensitivities to walnut, almond, hazelnut, pecan, cashew and pistachio. 

When a person with an allergy to a particular tree nut is exposed to that tree nut, proteins in the nut bind to specific antibodies made by the person’s immune system. This binding triggers the person’s immune defenses, leading to reaction symptoms that can be mild or very severe.

Research shows more than two percent of the child population is affected by allergies to tree nuts, and many will carry these allergies into adulthood. Peanuts and tree nuts account for 70 to 90 percent of all food-related deaths by anaphylaxis, whereas tree nuts alone stand for 18 to 40 percent.

A new discovery has shown that people who say they have a hazelnut allergy did not report any symptoms when exposed only to molecules found in hazelnuts. They were, however, instead sensitized to a molecule closely related to birch pollen.

Peanuts were not considered in the study as they are a legume, similar to beans and peas.

“We found that almost all individuals sensitized to hazelnut extract were also sensitized to birch and only few were sensitized to the allergens associated with more explicit symptoms. In fact, the majority of the participants sensitized to hazelnut did not report any symptoms to hazelnut and were sensitized only to a molecule that is closely related to birch pollen and hence is predicted to induce mild to no symptoms. Thus, most tree nut-sensitized individuals have no clinical tree nut allergy,” the authors write.

The study of more than 2,000 Swedish people tested as a child, a teenager and as an adult also reveals that while being sensitive to tree nuts is common, most people have never experienced symptoms. Early eczema, egg allergy and asthma were found to be factors signified associated with an increased risk of tree nut allergies when participants reached 24 years old.

The researchers also found allergen molecules were better diagnostic tools for predicting allergic symptoms to tree nuts compared with analyzing allergen extracts, which can lead to misdiagnosis.

“This study increases the understanding of tree nut allergy in a general population, followed from infancy up to adulthood. For example, our study reveals that most extract‐based tree nut‐sensitized individuals do not have tree nut allergy and hence extract-based testing for tree nuts without a specific clinical suspicion should not be performed,” the authors conclude.

The findings are published in the journal Clinical and Experimental Allergy.

South West News Service writer Joe Morgan contributed to this report.