Certain Component of Particulate Matter May Have Harmful Implications for Asthma

In a new paper, researchers are analyzing findings from a study of the association between air pollution and asthma in low- and middle-income countries, which account for more than 92% of pollution-related deaths. Based on the study findings, one component of pollution may be particularly harmful for asthma.

These findings were published recently in The Journal of Allergy and Clinical Immunology.

The researchers wrote of the implications of the study, in which Wang, et al. detailed an association between asthma and exposure to particulate matter less than or equal to 2.5 mcm (PM_2.5). The findings of the study pointed to an increased chance of self-reported asthma associated with exposure to elevated levels of PM_2.5.

“It is imperative that we, as researchers, educate and collaborate with policymakers to prioritize our understanding of how the complex mixtures we breathe influence human health while we develop strategies to protect our environment,” urged the authors of the new paper. “Innovative and cost-effective strategies to reduce [ammonia] emissions to reduce the burden of PM_2.5 are only a first step in a global effort to protect human health.”

The cross-sectional study comprised 45,000 adults from countries that included China, India, and Mexico. In addition to a general association between asthma and PM_2.5, analyses showed that each of its 5 individual components—black carbon, organic carbon, sulfate, ammonium (NH4+), and nitrate—were associated with an increased risk of asthma. The findings come as new evidence suggests that exploring the individual components of PM, rather than PM as a whole, may allow for a more accurate account of the impact of PM, which has a heterogenous makeup.

NH4+ had the highest risk of asthma, with every 1 SD increase (adjusted odds ratio, 1.28; 95% CI, 1.17-1.41). In a counterfactual analysis that estimated the number of preventable asthma cases associated with each of the components, NH4+ was also associated with the largest decrease in cases of asthma, with a 22% reduction (95% CI, 18.64%-25.84%). According to the authors of the new paper, the study findings indicate that NH4+ is harmful for asthma.

“This study has several strengths, including the large size of the cohort, approximately equal distribution of urban and rural sites, and a multinational design with inclusion of low- and middle-income countries, which have not been sufficiently represented in previous studies,” explained the authors. “Importantly, this study excluded children and did not take into account the relationship between cumulative exposure to PM_2.5 over the lifetime and odds of asthma. It is conceivable that the reduction in asthma incidence observed may be an underestimation of the true effect.”

The researchers wrote of other limitations of the study, including a lack of data on the age of asthma onset, asthma severity, health care costs associated with exposure, and the prevalence of comorbid chronic obstructive pulmonary disease.

Reference

Burbank AJ, Kesic MJ, Hernandez ML. From the farm to the big city: emerging health effects of agricultural emissions on asthma. J Allergy Clin Immunol. Published online April 25, 2022. doi:10.1016/j.jaci.2022.04.018