Mice were fed hazelnut extract with or without prior administration of omeprazole (a proton-pump inhibitor) or concurrent administration of sulcrafate (which has antacid activity). The doses of the drugs were equivalent to what would be given to humans, on a body-weight basis. Mice given the antiulcer drugs, but not the other mice, formed anaphylactogenic IgG1 toward hazelnut and developed type I skin reactivity to hazelnut extract. In a second study, 153 patients (mean age, 65.9 years) from a gastroenterology clinic who had been taking H2-blockers or proton pump inhibitors for 3 months because of dyspepsia or chronic gastritis were screened for specific IgE to hazelnut and inhalant allergens. Five patients (3.3%) had hazelnut-specific IgE, 4 of the 5 showed specific skin reactivity, 3 of the 5 had a positive reaction to oral provocation, and 2 of the 5 had a food allergy to hazelnut. None of these 5 patients showed sensitization to pollens that cross-react with hazelnut. Of 50 other patients from the same clinic who were not receiving antiulcer drugs, none showed evidence of sensitization to hazelnut allergens. The researchers concluded that the use of antiulcer drugs may lead to the development of immediate-type hypersensitivity toward hazelnut.

Comment: Hazelnut is the most frequent cause of IgE-mediated food allergy, with a prevalence of 21-53% in patients with food allergies in Europe. In approximately 5% of nut-allergic patients, severe systemic reactions (including asthma and hypotension) have been reported. While hazelnut allergy typically results from sensitization to cross-reacting pollen, severe allergic reactions to hazelnuts can occur without associated pollen allergy. Oral sensitization to hazelnut could presumably occur if antigens reach the intestinal mucosa intact. However, most of the major allergens in hazelnut extracts are not resistant to gastric and pancreatic digestion and, therefore, do not act as classic food allergens. On the other hand, such antigens might survive the digestive process intact, if the gastric acid secretion is blocked or neutralized.

Scholl I, et al. Antiulcer drugs promote oral sensitization and hypersensitivity to hazelnut allergens in BALB/c mice and humans. Am J Clin Nutr 2005;81:154-160.