High grass pollen associated with lower lung function in children with food allergies
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Increasing short-term exposure to ambient grass pollen was associated with reversible obstructive lung function deficits in children with allergic disease, researchers reported in The Journal of Allergy and Clinical Immunology: In Practice.
“Pollen exposure can trigger adverse respiratory outcomes in people with asthma and allergic rhinitis, but the risk of such exacerbations in people with no known allergic respiratory disease or those with other types of allergic diseases such as eczema or food allergy is unknown,” N. Sabrina Idrose, MSc, a PhD student and research assistant at University of Melbourne in Australia, told Healio.
“Children with food allergies or eczema typically have an increased risk of asthma and lower lung function. Therefore, we hypothesized that at least for some of these children, pollen exposure may induce immune activation in the airways, resulting in lung function impairment,” Idrose said.
The study included 641 children (53.2% male; mean age, 6.3 years; range, 5.8-8.7) in Melbourne who were part of the 6-year follow-up of the HealthNuts population-based study of children with food allergy between 2013 and 2016.
Clinicians measured each child’s pre-bronchodilator and post-bronchodilator spirometry and recorded forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), FEV1/FVC ratio and mid-forced expiratory flow (FEF25-75%).
Children were tested during four grass pollen seasons spanning 368 days total, with 69% of these days defined as having low pollen counts of less than 20 grains/m3, 20% as moderate with 20 grains/m3 to 49 grains/m3 and 11% with high counts of at least 50 grains/m3, as reported by the University of Melbourne School of BioSciences.
Researchers also considered the lag effects of ambient pollen exposure, including 1, 2 and 3 days prior to clinical testing (lag 1, 2 and 3), in addition to the concentrations on the day of testing (lag 0), and they calculated coefficients (coef.) to measure the effect size per each 20 grain/m3 increase in grass pollen within vs. outside the pollen season.
The study’s findings
The researchers found no overall association between grass pollen concentrations and pre-bronchodilator or post-bronchodilator lung function, although they did observe multiple interactions between pre-bronchodilator lung function and allergic diseases.
Specifically, there was an association between grass pollen concentration and obstructive lung function in children with food allergy, current asthma, hay fever or eczema, with consistent results for changes in bronchodilator responsiveness (BDR) for FEV1 and FVC.
“We observed the greatest and most consistent increase in risk of reversible obstructive lung function deficits in children with food allergy, with evidence of both large and medium-small airway involvement,” Idrose said.
For children classified with any food sensitization and allergy status, the researchers found evidence for an interaction for FEV1/FVC ratio, FEF25-75% and absolute BDR — or the absolute change in mLs from pre-bronchodilator values to post-bronchodilator values — but not for FEV1 or FVC alone.
Also, there was an association between increasing ambient grass pollen and a lower FEV1/FVC ratio z score (coef., –0.5; 95% CI, –0.8 to –0.2) and FEF25-75% z score (coef., –0.4; 95% CI, –0.6 to –0.04) at every lag and increased BDR at lags 2 (coef., 31 mL; 95% CI, –0.005 to 62) and 3 (coef., 36 mL; 95% CI, 2.2-72) in participants with food allergies but not in patients who were food-sensitized tolerant or who had no food sensitizations or allergies.
The researchers also found a modest association between increasing ambient grass pollen concentration and reduced FEF25-75% (coef., –0.2; 95% CI, –0.4 to 0.05) at lag 1 and increased BDR (coef., 26 mL; 95% CI, 26; –2 to 54) at lag 2 among participants with current asthma but not in those without.
Accounting for current hay fever or eczema, the researchers noted a modest association with increased BDR in participants who had current hay fever (coef., 24 mL; 95% CI, –0.4 to 50) or eczema (coef., 18 mL; 95% CI, –8 to 44) but not among those without.
However, the researchers did not find any evidence of an interaction pertaining to grass pollen sensitization or family history of allergic disease, nor was there evidence for an association between pollen season of testing per se and lung function.
There also was no evidence of interaction between grass pollen concentrations and grass pollen sensitization on lung function or of an association between whether the participants were tested during grass pollen season or not as an exposure. According to Idrose, this suggests that children who are sensitized to grass pollen may not be at risk for airway obstruction on high pollen days.
“However, only 16% of participants were grass pollen sensitized. So, this finding could be explained by insufficient numbers in our sample. We also did not collect data on serum pollen-specific IgE levels, so we were unable to investigate the variation that could have been provided by this measure,” she said.
Overall, the results show that high grass pollen exposure may worsen global airway disease among children with food allergy, but there was no association between grass pollen concentration and lung function in children who were tolerant of food sensitization.
Additionally, current asthma modified the association between grass pollen concentration and lung function, whereas there were more modest increases in absolute BDR with increased ambient grass pollen concentration among children with current eczema or hay fever.
“In children with any allergic disease, most associations were observed at lag day 2, indicating the ambient grass pollen may only affect the lungs approximately 48 hours after exposure,” Idrose said.
“This is consistent with known pathophysiology of induced allergic airway inflammation, where peak immune response to pollen, such as eosinophils recruitment, has shown to occur within 3 days of exposure,” she continued.
Next steps in care and research
With a better understanding of this relationship, clinicians may be able to improve the timing and targeting of their preventive therapy during pollen season.
“Although children with current asthma, hay fever or eczema were shown to have a higher risk of airway obstruction as grass pollen levels increased, the changes in lung function were not as statistically significant as those with food allergy,” Idrose said.
“We speculate that children with these conditions may have poorer lung function at baseline, so the changes may not be as significant and/or they may have their conditions deliberately well-controlled, eg, by using asthma-preventive medications and/or by limiting time outdoors, during the grass pollen season,” Idrose continued.
This is the first study to investigate the relationship between concentrations of grass pollen and changes in lung function among children with food allergy or eczema, according to Idrose.
“If these findings are confirmed in further research, doctors can incorporate this knowledge into clinical practice so that these children are proactively managed for asthma activity during and preferably before high grass pollen periods,” she said.
There were insufficient numbers in this study’s sample to investigate specific food allergies, Idrose said, noting the multiple interactions among allergic reactions that usually coexist within individuals. Further research, she added, will be necessary to determine these associations.
“It will be interesting to see if children with egg allergy respond differently to increasing grass pollen concentrations, compared with children with peanut allergy, and if the associations are still present once those with coexisting allergic respiratory disease are excluded from the analysis,” Idrose said.
In the meanwhile, the researchers wrote, caregivers of children with food allergy need to be educated about the potential adverse effects of outdoor allergen exposures, while doctors should incorporate this knowledge into their clinical guidelines to better manage asthma activity both before and during periods of high grass pollen.
“Pollen communication outreach, which is often a cost-effective tool, could include all families with children with any allergic disease, rather than only those with asthma or hay fever,” she said.
For more information:
N. Sabrina Idrose, MSc, can be reached at sabrina.idrose@unimelb@edu.au.