Bright I. Nwaru, PhD

Credit: University of Gothenburg

The first estimates on the prevalence of specific tree nut allergies (TNA) and tree nut sensitization were revealed in new findings, with the data including walnuts, hazelnuts, almonds, Brazil nuts, pistachios, cashews, pecan nuts.¹

These findings were the result of a meta-analysis of the 2014 European Academy of Allergy and Clinical Immunology (EAACI) systematic review of the European prevalence of food allergies and sensitization, with studies in the review being from 2000 - 2012.²

The new meta-analysis was led by Bright I. Nwaru, PhD, from the Krefting Research Centre at the University of Gothenburg in Sweden. Nwaru and colleagues sought to provide updates regarding several specific nut types to broaden the understanding of TNAs.

“In the current work, we present the prevalence estimates for specific TNA/sensitization, including hazelnut, walnut, almond, Brazil nut, cashew nut, pistachio, chestnut, pecan nut, and pine nut based on data published between 2000 and 2021,” Nwaru and colleagues wrote. “There were no available data on macadamia nut allergy.”

Background and Findings

The protocol was registered with the International Prospective Register of Systematic Reviews (PROSPERO), and their search strategy was drawn from the EAACI’s 2014 review and conducted using 6 electronic databases (MEDLINE, EMBASE, CINAHL, Web of Science, Cochrane Library, and Scopus). They looked into studies which had been published from September 2012 - June 2021.

The investigators’ search included all types of tree nuts and utilized both older and newer keywords to account for database developments. The team did not apply any language restrictions to the studies, and they used translations whenever they were deemed necessary.

The types of research considered by the research team to be eligible included clinical trials, systematic reviews, cohort, case-control studies,cross-sectional, and routine healthcare studies. The team excluded discussion papers, narrative reviews, non-research letters,case-series, editorials, case-studies, and animal studies.

The study involved the use of 2 pairs of independent reviewers screening the utilized studies by abstract, title, and full text. Their review assessed several types of tree nuts, with the goal being to provide data on the prevalence, incidence, and trends in allergies.

The data found on lifetime and point prevalence were included by the investigators in the meta-analysis. IgE-mediated and non-IgE-mediated allergy differentiation was found not to be possible as a result of the available research’s lack of differentiation.

The investigators examined several types of prevalence outcomes that were related to self-reported allergies to tree nuts, clinician-diagnosed allergies, symptoms plus sIgE or skin prick test (SPT) positivity, specific immunoglobulin E (sIgE) and SPT positivity, and positive results of oral food challenges (OFCs) or double-blind placebo-controlled food challenges (DBPCFCs).

The research team’s meta-analysis was determined to have been meaningful when outcomes with at least 3 available records were assessed. The investigators’ analysis ended up encompassing 32 studies.

Overall, the team explored various tree nuts, with walnuts, hazelnuts, almonds, Brazil nuts and cashews being the main focus for their meta-analysis. Their main findings showed that there was a lifetime self-reported prevalence of 0.4% (0.2–0.9) for walnuts and 0.8% (95% CI 0.5–1.1) for hazelnuts.

The investigators reported that the point self-reported rates of prevalence were shown to be 4.0% (2.9–5.2) for hazelnuts, 2.0% (1.1–2.9) for almonds, 3.4% (2.0–4.9) for Brazil nuts, and 1.8% (1.1–2.5) for walnuts. They also noted that point prevalence of TNA had been confirmed with food challenges and stood at 0.04% (0.0–0.1) for hazelnuts and at 0.02% (0.01–0.1) for walnuts.

Despite these findings, as a result of limited data availability, the investigators could not identify any substantial or consistent distinctions in relation to age groups or geographical regions around Europe.

“More studies are required on this topic, and given the observed methodological heterogeneity of included studies, implementing more standardized approaches to definition and assessment of TNA across Europe will further advance the field,” they wrote.

References

1. ^{Spolidoro, GCI, Lisik, D, Nyassi, S, et al. Prevalence of tree nut allergy in Europe: A systematic review and meta-analysis. Allergy. 2023; 00: 1-22. doi:10.1111/all.15905.}
2. ^{Nwaru BI, Hickstein L, Panesar SS, et al. The epidemiology of food allergy in Europe: a systematic review and meta-analysis. Allergy. 2014; 69(1): 62-75.}