High ambient grass pollen levels may increase food sensitization risk in children
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Children exposed to persistently high levels of ambient grass pollen may have an increased risk for food sensitization but not allergy, according to data presented at the European Academy of Allergy and Clinical Immunology Hybrid Congress.
The researchers hypothesized that short-term pollen exposure may contribute to increased food sensitization and allergies, as well as to an increased reaction threshold to oral food challenge.
“Our recently published systematic review showed that short-term pollen exposure can trigger type 2 immune responses. We hypothesized that this can lower the manifestation of other allergic diseases,” author N. Sabrina Idrose, a PhD student and research assistant at University of Melbourne, told Healio.
“Pollen and food allergens can also cross-react, resulting in the pollen-food allergy syndrome,” Idrose added. “Although this is well-established, the role of short-term pollen exposure in food allergy has not been investigated in a population-based sample.”
The researchers used data from HealthNuts, a population-based cohort comprising 5,276 children who were recruited at the age of 12 months and who underwent follow-up at the age of 6 years.
Idrose and colleagues evaluated data of 1,108 of these children at the age of 12 months and 675 of these children at the age of 6 years who were examined during the grass pollen season.
Researchers measured grass pollen levels by volumetric spore trap (grains/m3) located 15 m above the ground. These researchers also considered pollen exposure on the day of testing (lag 0), up to 3 days before testing (lag 1-lag 3) and cumulatively (lag 0-3).
Outcomes included sensitization to specific foods as measured by a skin-prick test at 12 months ( 2 mm) and at 6 years ( 3 mm). Researcher also used logistic or quantile regression models to evaluate challenge-confirmed food allergy, reaction threshold to oral food challenge based on a cumulative dose given before a reaction occurred and serum food-specific IgE levels.
The researchers found an association between grass pollen levels at lag 0-3, with up to 25% higher probability of sensitization to all food allergens at 6 years but not at 12 months.
Grass pollen levels also appeared associated with peanut sensitization at 12 months, with up to 60% higher probability among children with a family history of food allergy and up to 75% higher probably among those with severe eczema.
Although grass pollen levels did not appear associated with the probability of challenge-confirmed food allergy in both age groups, the researchers found an association between grass pollen levels and a lower median reaction threshold to oral food challenge (at lag 0) and higher median serum-specific IgE levels at lag 1 and lag 0-3 among children aged 12 months with peanut allergies.
“Among those who were peanut allergic, increased grass pollen concentrations were associated with higher serum food-specific IgE levels and a lower reaction threshold to oral food challenges, which means that the cumulative dose needed to trigger a reaction was lower,” Idrose said.
Grass pollen exposure may then trigger type 2 immune responses through immune activation, or peanut and grass pollen cross-reactivity, but only if allergy was already present, Idrose said.
“In other words, peanut allergic children could be at risk [for] a more severe reaction when grass pollen levels are high,” she said.
The fact that there was no variation in the results between those who were sensitized to grass pollen and those who were not sensitized was surprising, Idrose said.
“Pollen-food allergy syndrome usually occurs in those who are pollen sensitized, so we expected the results to be stronger in this group,” she said. “However, this lack of observed association could be due to limited sample size, as we only had 675 participants in total, and only 15% of the participants were sensitized to grass pollen.”
Idrose said this was the first study to investigate these associations and that further research is needed to confirm the findings before recommendations are made. But for now, she said, physicians can choose to advise the parents and caregivers of children with peanut allergies to limit their time outdoors when grass pollen levels are at least 50 grains/m3.
“Children with food allergies should be more careful and perhaps limit their time outdoors during the peak of the grass pollen season,” she said, adding that another study she and colleagues presented at EAACI Congress showed food-allergic children had increased risk for obstructive lung function deficits consistent with asthma as grass pollen levels increased.
“So, there is mounting evidence that high grass pollen levels may be detrimental to food-allergic children, in terms of increasing their risk [for] asthma and potentially inducing more severe food allergic reactions,” Idrose said.
Idrose noted the need to continue researching these associations among children.
“I propose to assess the associations between pollen levels and other outcomes such as the severity of reactions to oral food challenges, ie, does the severity increase as pollen levels increase; the reaction thresholds to oral food challenges and food-specific IgE levels in older children; mutually exclusive food sensitization groups, eg, egg-sensitized children without peanut sensitization; and T-cell subsets and cytokines,” she said.
For more information:
N. Sabrina Idrose can be reached at nidrose@student.unimelb.edu.au.