Exposure to air pollution during first three years of life linked with increased risk of childhood asthma: JAMA

"Mean nitrogen dioxide (NO2) and mean fine particulate matter (PM2.5) air pollution during the first three years of life were linked with asthma incidence by early and middle childhood, after adjusting for individual-level characteristics," the researchers reported in their study published in JAMA Network Open.

The association of ambient pollution (NO2 or PM2.5) with incident asthma was modified by individual-level and community-level socioeconomic circumstances, including maternal education and race.

Air pollution is a near-ubiquitous exposure and contributes largely to disease and premature death in the world, including for children. Air pollution exposure has been consistently linked with respiratory morbidity, including exacerbation of asthma and wheezing in children. Various reviews on air pollution, asthma, and respiratory symptoms in children concluded that outdoor traffic pollution contributes to childhood asthma development. However, many studies lack the racial and ethnic, geographic, and socioeconomic diversity to evaluate susceptibility by individual-level and community-level contextual factors.

Against the above background, Antonella Zanobetti, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, and colleagues aimed to examine early life exposure to PM2.5 and NO2 air pollution and asthma risk by early and middle childhood. They also determined whether individual and community-level characteristics modify associations between air pollution exposure and asthma.

For this purpose, the researchers included children enrolled in cohorts participating in the Children’s Respiratory and Environmental Workgroup consortium. The location of the birth cohorts was throughout the US, recruited between 1987 and 2007, and followed up through 11 years.

The survival analysis was adjusted for parental asthma, mother’s education, child’s race and ethnicity, smoking during pregnancy, sex, neighbourhood characteristics, and cohort. Statistical analysis was performed from February 2022 to December 2023.

The study's main outcomes were caregiver reports of physician-diagnosed asthma through early (age 4 years) and middle (age 11 years) childhood.

The study led to the following findings:

• Among 5279 included children, 51.5% were male; 24.7% of children had asthma by 11 years of age, and 18.1% had asthma by 4 years of age.
• Mean values of pollutants over the first 3 years of life were associated with asthma incidence.
• A 1 IQR increase in NO2 (6.1 μg/m3) was associated with increased asthma incidence among children younger than 5 years (HR, 1.25) and children younger than 11 years (HR, 1.22).
• A 1 IQR increase in PM2.5 (3.4 μg/m3) was associated with increased asthma incidence among children younger than 5 years (HR, 1.31) and children younger than 11 years (OR, 1.23).
• Associations of PM2.5 or NO2 with asthma were increased when mothers had less than a high school diploma, among Black children, in communities with fewer child opportunities, and in census tracts with a higher percentage of Black population and population density; for example, there was a significantly higher association between PM2.5 and asthma incidence by younger than 5 years of age in Black children (HR, 1.60) compared with White children (HR, 1.17).

"Air pollution continues to be a global burden with adverse consequences on childhood health," the researchers wrote.

"Lowering asthma risk in the US requires reduction and regulation of air pollution combined with the creation of greater educational, environmental, and health equity at a community level," they concluded.

Reference:

Zanobetti A, Ryan PH, Coull BA, et al. Early-Life Exposure to Air Pollution and Childhood Asthma Cumulative Incidence in the ECHO CREW Consortium. JAMA Netw Open. 2024;7(2):e240535. doi:10.1001/jamanetworkopen.2024.0535