Early-life ozone exposure associated with increased risk of childhood asthma and wheezing

Early-life ozone exposure associated with increased risk of childhood asthma and wheezing

A new study finds that children exposed to higher ozone levels in the first two years are significantly more likely to develop asthma and wheezing by age six, highlighting the urgent need for early environmental interventions.

A current oneJama Network OpenThe study examines the effects of exposure to childhood asthma and wheezing alone in children and in combination with other air pollutants.

Asthma in children

In 2021, approximately 6.5% of children living in the United States were diagnosed with asthma, the most common chronic disease affecting children worldwide. Exposure to various environmental pollutants has been implicated in the development of asthma, some of which include fine particles (PM2.5), nitrogen dioxide (NO2), and O3.

To date, few studies have evaluated how long-term exposure to O3 affects asthma progression in children. Additionally, existing studies have yielded mixed results without considering how other circulating pollutants in the environment may also contribute to observed asthma exacerbations.

It is critical to gain additional insight into the relationship between O3 exposure and chronic respiratory disease to support advances in preventive strategies and future treatments. It is particularly important to understand whether early life exposure to O3 affects children's health, as this period is crucial for their immune and respiratory development.

About the study

The researchers hypothesized that greater exposure to ambient O3, independently or in multipollutant models, would increase the likelihood of asthma and wheezing across all age groups.

To this end, the association between O3 exposure in the first two years of life and the risk of asthma and wheezing later in life was determined. The influence of O3 exposure in a multipollutant mixture on asthma and wheezing between four and six years was also analyzed to predict disease progression up to nine years.

Study participants were recruited from three prospective pediatric cohorts of Environmental Influences on Prenatal and Early Childhood Pathways to Child Health Consortium (Echo-Pathways). All eligible candidates had a valid geocoded addressing history between birth and two years and comprehensive data on their respiratory condition between four and eight to eight to nine years. Preterm infants were excluded from the cohort.

O3 exposures between birth and two years were measured in parts per billion (PPB) using the point-based national spatiotemporal model. This model took into account pollutant concentrations and hundreds of geographic covariates from the regulator's monitors and research campaigns. Multipollutant models assessed NO2 (PPB) and PM2.5 (μg/M3) exposure for equal age groups.

Information on asthma onset and wheezing trajectories in specific age groups was provided by caregivers in respiratory surveys.

Logistic regression analysis was performed using staged covariate modeling to calculate odds ratios (ORS) of asthma incidence due to early life O3 exposure. Multinomial regressions were used to compare wheezing phenotypes with nonwheezing children serving as a reference population.

Study results

A total of 1,188 participants were selected from three cohorts with a mean age of 4.6 years at four to six years of age, of which 51.7% were female and 81.9% had mothers with no history of asthma. At this time, 12.3% of children already had asthma and 15.8% had current wheezing.

At eight to nine years of attendance, the average age of participants was 8.9 years and 9.4% had developed strict asthma. Based on their respiratory assessments, these children were divided into different groups, with 59.5% of children classified as never wheezing, 20.8% as early wheezing, 11.3% as late wheezing, and 8.3% as persistent wheezing.

For site-specific O3 distributions, the mean ambient O3 concentration between birth and age was 26.1 ppb. Postnatal pollutants of 8.8 ppb NO2 and 9.3 μg/m3 PM2.5 were also recorded.

The primary model analysis found that a two PPB increase in early life O3 exposure was associated with one or 1.31 for current asthma and 1.30 for current wheeze at four to six years of age.

Compared to primary model results, secondary models with expanded covariate adjustment yielded ORS of 1.26 for current asthma and 1.27 for wheezing. Prenatal and co-pollutant adjustment for early life O3 and respiratory outcomes were not associated with significant differences.

A combined mixture of O3, NO2 and PM2.5 was associated with an increased risk of asthma; However, this mixture did not have a significant impact on the development of wheezing. Bivariate interactions identified consistent associations between O3 and current asthma at all concentrations of NO2.

Evidence for associations between O3 and current asthma and wheezing was consistent for PM2.5 at the 50th or 90th percentile, but not for lower PM2.5 levels.

Regulating and reducing exposure to ambient O3 can help reduce the significant public health burden of childhood asthma. “

Conclusions

Children exposed to O3 in the first two years of life are more likely to develop asthma and wheeze between the ages of four and six, but not between the ages of eight and nine. In contrast to lower O3 concentrations within the mixture, higher concentrations increased the risks of asthma and wheezing in children.

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