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Decreased exposure to air pollutants in California reduced asthma incidence in children

Erika Garcia

Decreases in regional air pollutants were associated with reductions in asthma incidence among children in Southern California from 1993 to 2014, researchers reported.

“Reductions in childhood asthma could have economic, long-term health, quality of life and overall societal benefits,” Erika Garcia, PhD, researcher in the department of preventive medicine at Keck School of Medicine of the University of Southern California, told Healio Pulmonology. “Given improvements in air quality throughout the U.S. and around the world in the past several decades, it would be beneficial to examine whether the same trends of lower air pollution and lower rates of asthma are observed elsewhere. Furthermore, examining age windows of exposure could provide us with a better sense of when children are most vulnerable to the effects of air pollution exposure in the development of new-onset asthma.”

The researchers used a multilevel longitudinal cohort composed of 4,140 children (mean age, 9.5 years; 52.6% girls; 58.6% white) with no history of asthma pooled from the Southern California Children’s Health Study during three time periods of air pollution decline: 1993 to 2001, 1996 to 2004, and 2006 to 2014.

Data were routinely gathered in the baseline year for each of three cohorts on annual mean community-level ozone, nitrogen dioxide, and particulate matter less than 10 m (PM) and particulate matter less than 2.5 m (PM). Cases of incident asthma were collected via questionnaires during follow-up.

Researchers reported 525 incident cases of asthma among the entire cohort.

Decreased exposure to ambient nitrogen dioxide and PM were significantly associated with lower asthma incidence between 1993 and 2014. The incidence rate ratio (IRR) for nitrogen dioxide was 0.8 (95% CI, 0.71-0.9), for a median reduction of 4.3 parts per billion, with an absolute incidence rate decrease of 0.83 cases per 100 person-years. The IRR for PM was 0.81 (95% CI, 0.67-0.98), for a median reduction of 8.1 g/m, with an absolute incidence rate decrease of 1.53 cases per 100 person-years.

However, no statistically significant associations were found for ozone or PM.

“New asthma cases in children can be reduced through improvements in air quality,” Garcia said. “That being said, there must be continued efforts to reduce air pollution in the Los Angeles region as well as other high pollution areas. The greater Los Angeles region ranks as one of the most polluted regions in our country for fine particulate matter and ozone. During the past few years, we have seen an uptick in nitrogen dioxide levels in the South Coast Air Basin. With more people and more cars, and ports getting busier, air pollution may continue to increase. Policies geared towards air quality improvement will benefit all communities, especially the most vulnerable who reside near ports and freight corridors.”

George D. Thurston, ScD, director of the Program in Exposure Assessment and Human Health Effects in the department of environmental medicine at New York University School of Medicine, and Mary B. Rice, MD, MPH, pulmonary and critical care physician at Beth Israel Deaconess Medical Center, mirrored Garcia’s sentiment in an accompanying editorial.

“[This study] is particularly timely and provides new evidence that past regulatory efforts to improve air quality have provided substantial health benefits because fewer children have developed a chronic lung disease,” they wrote. “The improvements in air quality evaluated in this study were also enjoyed by many communities across the United States because of the Clean Air Act, a landmark 1970 legislation that has been credited with improving U.S. life expectancy. This study, in combination with the published medical literature linking long-term air pollution exposure and risk for new onset asthma, is robust and worthy of inclusion in cost-benefit analyses of future regulatory efforts to control air pollution from fossil fuel combustion.” – by Jennifer Southall

Disclosures: The authors and Thurston report no relevant financial disclosures. Rice reports receiving grants from the National Institute of Environmental Health Sciences and ATS Foundation/American Lung Association and is the 2019 chair of the Environmental Health Policy Committee of the American Thoracic Society.