Ozone Air Pollution Linked to Kids' Asthma, Wheeze

Early-life exposure to even relatively low levels of ozone air pollution was associated with asthma and wheeze in childhood, a prospective study showed.

In a study of six U.S. cities with low annual ozone concentrations, each 2 ppb higher level exposure in the first 2 years of life correlated with a 31% higher likelihood of asthma and 30% elevated risk of wheeze at age 4-6 years, Catherine J. Karr, MD, PhD, of the University of Washington in Seattle, and colleagues reported in JAMA Network Openopens in a new tab or window.

The associations for 4- to 6-year-olds were seen both for ozone independently and when considered in mixtures of fine particulate matter and nitrogen dioxide. However, the risks were not significant at age 8-9 years.

Ozone “represents the criteria air pollutant most commonly exceeded among U.S. children,” the researchers wrote. Thus, “[r]egulating and reducing exposure to ambient O₃ [ozone] may help reduce the significant public health burden of asthma among U.S. children.”

The findings come at a time when the Environmental Protection Agency (EPA) has announced cuts in enforcement of clean air and clean water rulesopens in a new tab or window. EPA ambient air quality standardsopens in a new tab or window limit ozone to 70 ppb (0.070 ppm); mean exposure in the study was 26.1 ppb. Other criteria air pollutants regulated by the EPA include particle pollution, carbon monoxide, lead, sulfur dioxide, and nitrogen dioxide.

Short-term exposure to ozone has been consistently linked to acute asthma exacerbation in previous studies, but prior findings on chronic exposure have been mixed.

“Animal toxicological studies support the biological plausibility of O₃ developmental toxicity and indicate a more pronounced effect from O₃ exposures during early life,” Karr’s group noted. “This period coincides with immense immune and respiratory development among children that supports a critical window for O₃ exposures during early life.”

The study was a pooled analysis of data from the prospective ECHO-PATHWAYS consortium (2007-2023) across three prospective pediatric cohorts: CANDLE in the Memphis, Tennessee area; PATHWAYS-GAPPS in Seattle and Yakima, Washington; and TIDES, which enrolled in Minneapolis, San Francisco, Seattle, and Rochester, New York. Of the 3,072 participants total across those studies, 1,188 children were included in the analysis who had complete airway surveys, complete address histories from age 0-2 years for assessment of pollutant concentrations at their home address, and a full-term birth at greater than 37 weeks.

Slightly more than half of the children were female, and 56% had a mother with at least a bachelor’s degree.

The average age was 4.5 when wheeze and asthma were assessed by caregiver-completed airway surveys using the International Study of Asthma and Allergies in Childhood (ISAAC). At that 4-6-year visit, 12.3% had asthma and 15.8% had wheeze.

Mean ozone concentration exposure at 0-2 years of age was 26.1 ppb. Each additional 2 ppb of exposure carried a hazard ratio of 1.31 (95% CI 1.02-1.68) for current asthma and 1.30 (95% CI 1.05-1.64) for current wheeze at age 4 to 6 years.

Analyses were adjusted for child sex, age at assessment, postnatal secondhand smoke exposure, breastfeeding duration, and furry pet ownership in the first year of life as well as socioeconomic and neighborhood factors.

“Within mixture, higher O₃ was consistently associated with higher asthma and wheeze when other pollutants were held at the median, although pairwise associations differed by pollutant,” the researchers noted. Bayesian kernel machine regression suggested ozone contributed to higher asthma at and above median concentrations of nitrogen dioxide and fine particulate matter, “indicating possible effect modification by these other criteria pollutants.”

Early-life ozone exposure didn’t correlate with asthma under strict criteria at age 8-9 years or with wheezing trajectories at ages 4-6 or 8-9 years.

“Null findings at this older age may indicate that airway outcome development is related to more proximal ambient O₃ concentrations, although more research is needed in this area,” Karr and colleagues suggested.

While they noted that their use of spatiotemporal derived ozone estimates “is an improvement within the field,” the researchers acknowledged that they didn’t have any personal or indoor measurements and they had to rely on caregiver report of asthma and wheeze.