Outdoor Pollen Exposure May Worsen Asthma Attacks

Is pollen a risk factor for asthma exacerbations? In one study, an association between pollen sensitization and asthma suggests how preventive measures in asthma control should consider pollen exposure and climate change.

“To our best knowledge, this is the first systematic review and meta-analysis to comprehensively summarize the relationships between pollen exposure and asthma exacerbation, as assessed through various respiratory outcomes,” wrote the researchers of this study.

The results of this systemic review were published in Allergy.

Pollen is a known risk factor for allergic rhinitis, and more recently was identified as a risk factor for asthma. However, few studies have evaluated the association between pollen exposure and asthma exacerbations. Furthermore, an increase in pollen concentrations due to climate change may be contributing to worsening allergy symptoms in individuals with moderate to severe asthma.

This study identified 3244 records from electronic databases, of which 270 full texts were evaluated, with 73 studies included in the final analysis. The studies used in the review shared the same study designs, populations, age ranges, and lags (measured in days) between pollen assessment and asthma exacerbation.

Although conducting meta-analysis for all outcomes was not possible, the researchers were able to conduct an analysis for severe asthma exacerbations associated with increases in . grass pollen, tree pollen, cypress, and ragweed exposure.

Most of these studies reported a strong association with worsening asthma-related hospitalizations and increased pollen concentrations. The strongest associations were found between asthma attacks and asthma-related emergency department (ED) admissions or hospitalizations and an increase of grass pollen concentration in the previous 2 days in children younger than 18 years.

In an analysis of 5 studies, a significant association was observed between severe asthma exacerbation (odds ratio [OR], 1.00; 95% CI, 1.00-1.01) and an increase in grass pollen concentrations from 0 to 50 pollen grains/m³ at a time lag of 0 to 2 days for patients under 18 years.

Additionally, 2 studies identified an association between asthma-related ED visits and tree pollen from a lag of 1 day. In addition, at a lag of 2 days, one of the studies reported a positive association, with a 100 grains/m³ increase in individuals younger than 18 years between lag 0 to 2. However, the second study, a case-crossover study reported no association. At lags of 3 and 4 days, the 2 studies reported a positive, but unclear association.

Although no meta-analysis was conducted in these 2 studies, a positive association was found when tree pollen concentrations increased from 0 to 50 grains/m³ between lag 0 to 2 (OR, 1.19; 95% CI, 1.17-1.21 and OR, 1.02; 95% CI, 0.99-1.04), respectively. Lastly, when tree pollen concentrations increased more than 50 grains/m³, no association was observed in the meta-analysis (OR, 1.00, 95% CI, 0.99-1.02).

Although inconsistent, the results suggest that tree pollen may increase asthma-related ED visits or admissions lagged up to 7 days overall in individuals younger than 18 years.

Despite some unclear associations, the researchers believe that outdoor pollen exposure may have an impact on asthma attacks and asthma-related hospitalizations, but that this association should be taken with caution, as more research is needed to determine these potential effects.

“Current evidence suggesting an impact of pollen on asthma exacerbation incite to propose recommendations and preventative measures to protect individuals during pollen seasons,” concluded the researchers. “However, further research is urgently warranted to evaluate whether they are effective.”

Reference

Annesi‐Maesano I, Cecchi L, Benedetta B, et al. Is exposure to pollen a risk factor for moderate and severe asthma exacerbations? Allergy. March 2023. doi:10.1111/all.15724