Asthma impacts over 6% of children in the U.S., rendering it the most prevalent chronic illness among youngsters across the country. It is challenging to pinpoint any specific origin, but one of the leading factors is air contamination: Research has indicated that inhaling air laden with elevated levels of fine particulate matter, nitrogen dioxide, and other environmental toxins can heighten the risk of asthma development in children. However, it remains ambiguous whether prolonged exposure to ozone during early childhood, the pollutant that most often surpasses U.S. air quality limits, plays a role in the condition.

Logan Dearborn, a doctoral candidate at the University of Washington, embarked on a study to uncover a potential connection. In an investigation released on April 2 in JAMA Network Open, Dearborn and associates discerned an intriguing pattern: Children who were exposed to higher quantities of ozone in their initial two years had a notably greater likelihood of being diagnosed with asthma or experiencing wheezing by ages 4-6; however, the researchers did not detect the heightened asthma risk at ages 8-9.

Even though the scientists could not determine the precise cause, possible reasons could include the evolving nature of asthma as children mature, leading to a potential decline in official diagnoses, along with the impact of additional risk factors and pollutants on asthma development as their lungs mature.

“It’s a perplexing observation,” remarked Dearborn, who directed the research in the UW Department of Environmental & Occupational Health Sciences. “We devoted a considerable amount of time contemplating this matter, and I am uncertain if we arrived at a fulfilling explanation. Nonetheless, these results are significant. Even if the effects are only manifest in early childhood, there are numerous associated healthcare expenses and pressures for families. The implications of managing this chronic disease at any life stage are considerable.”

This research utilized data from the Environmental influences on Child Health Outcomes (ECHO) initiative, a government-sponsored research study examining the impact of various environmental factors on children’s health. The researchers drew in 1,118 subjects from six cities, including Seattle and Yakima, who had low-risk pregnancies and answered validated surveys exploring whether their children had been diagnosed with asthma or experienced wheezing.

The researchers estimated exposure during the first two years of a child’s life using a model devised by co-author Dr. Joel Kaufman, a UW professor specializing in environmental and occupational health sciences, epidemiology, and medicine. They discovered that even a relatively slight increase in ozone exposure — 2 parts per billion — during a child’s initial two years correlated with a 31% rise in asthma and a 30% increase in wheezing at ages 4-6. There was no significant association found between asthma and wheezing risk at ages 8-9 with their early life ozone levels.

Researchers also examined how exposure to combinations of three prevalent air contaminants — ozone, nitrogen dioxide, and fine particulate matter (PM2.5) — influenced asthma outcomes. In this investigation, ozone prominently emerged as a standout factor.

“We assess patterns, and what we can infer from this analysis is that when ozone levels in the air pollution mix exceeded approximately 25 parts per billion, we noted an elevated probability of asthma irrespective of nitrogen dioxide concentration,” Dearborn stated. “We identified a correlation between ozone and asthma only when fine particulate matter concentrations were at or above median levels, providing novel evidence that the connection between ozone and childhood asthma may be influenced by the levels of other pollutants, such as fine particulate matter.”

The results of the study underscore the necessity for further investigation into the ramifications of prolonged ozone exposure in early life, according to Dearborn. Additional research could clarify why the augmented asthma risk associated with ozone is not obvious at ages 8-9 and whether this risk re-emerges later in childhood.

Meanwhile, Dearborn mentioned that researchers and public health authorities should focus more on the consequences of long-term ozone exposure.

“In the U.S., regulations on ozone are only based on very brief timeframes,” Dearborn stated. “There isn’t regulation for ozone over extended periods, and that’s where this analysis is relevant. Perhaps we should consider both short- and long-term limits for ozone regulation.”

Additional contributors include Catherine Karr, a UW professor of environmental and occupational health sciences and pediatrics in the UW School of Medicine; postdoctoral researchers Allison Sherris and Jianzhao Bi, research scientist Magali Blanco, and clinical associate professor Christine Loftus, all affiliated with the UW Department of Environmental & Occupational Health Sciences; Adam Szpiro, a UW professor of biostatistics; Aileen Andrade-Torres, a graduate student in the UW Department of Epidemiology; Mary Crocker from the Seattle Children’s Research Institute and an assistant professor of pediatrics at the UW School of Medicine; Margaret Adgent and Paul Moore from the Vanderbilt University Medical Center; Yu Ni from San Diego State University; Marnie Hazlehurst and Drew Day from the Seattle Children’s Research Institute; Ruby Nguyen from the University of Minnesota; Kaja LeWinn from the University of California, San Francisco; and Kecia Carroll from the Icahn School of Medicine at Mount Sinai in New York City.  

This study received funding from the National Institutes of Health’s ECHO-PATHWAYS initiative; the National Center for Advancing Translational Health Sciences; the National Heart, Lung, and Blood Institute; the National Institute of Environmental Health Sciences; the UW Pediatric and Reproductive Environmental Health Scholars K-12 initiative; the U.S. Environmental Protection Agency; the UW EDGE Center; the National Institute on Aging; and the Urban Child Institute.