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More stringent air quality standards may decrease childhood asthma incidence

Policies designed to reduce air pollutants could result in a lower incidence of childhood asthma, researchers reported in the Proceedings of the National Academy of Sciences.

In this study, Erika Garcia, PhD, MPH, from the department of preventive medicine at the Keck School of Medicine, University of Southern California, Los Angeles, and colleagues evaluated data on 4,140 children from three successive cohorts from the same nine communities in Southern California between 1993 and 2014 to estimate the incidence of asthma.

The average age at enrollment was 9.5 years, the average follow-up duration was 5.9 years and 525 incident asthma cases were identified.

From 1993 to 2006, the mean nitrogen dioxide concentration declined from 24 parts per billion (ppb) to 17.8 ppb and the mean concentration of particulate matter smaller than 2.5 µm (PM_2.5) declined from 20.8 µg/m³ to 13.7 µg/m³.

In analyses studying the effect of air pollutant reduction on asthma incidence, the researchers found that had the nitrogen dioxide concentrations remained the same, the estimated asthma incidence would have been 19.3% higher when compared with the natural course of exposure.

However, results also showed that greater decreases in nitrogen dioxide concentrations during the same period would have likely resulted in greater reductions in asthma incidence.

Specifically, in a hypothetical intervention in which nitrogen dioxide concentrations decreased by 30%, the asthma incidence was 27.6% lower when compared with the natural course of exposure. Further, had there been complete adherence to a hypothetical air quality standard of 10 ppb, the estimated asthma incidence would have been 39.2% lower.

As expected, the effect size was less pronounced with more moderate reductions in nitrogen dioxide concentrations, including a smaller 19.6% decrease in estimated asthma incidence with a 20-ppb reduction in nitrogen dioxide concentration when compared with the natural course of exposure.

Results from sensitivity analyses yielded similar findings.

Although still statistically significant, less of an effect was seen with hypothetical interventions for PM_2.5. Without any reduction in PM_2.5 concentration from 1993 on, the estimated asthma incidence would have been 9.8% higher compared with the natural course. However, with a 30% reduction in PM_2.5 concentration, the estimated asthma incidence would have been 12.8% lower compared with the natural course, according to the data.

“Our study demonstrated a large potential public health benefit of air pollution reduction, both realized and hypothetical improvements, in reduced asthma incidence in children. Because regional air pollution levels are experienced by all community members, albeit with some variation in individual exposure due to differences in behavior and microenvironments’ concentrations, shift in exposure at the population level have the potential for large benefits in reduced incidence rate of an outcome,” the researchers wrote. “These findings were observed in communities at [nitrogen dioxide] concentrations well below the current U.S. Environmental Protection Agency annual standard of 53 ppb, indicating that there may be public health benefits in reevaluating air quality standards.” – by Melissa Foster

Disclosures: The authors report no relevant financial disclosures.