Fine particulate matter (PM2.5) and nitrogen oxide (NO2) exposure during the first 3 years of life are associated with an increased incidence of asthma by early and middle childhood, according to a study in JAMA Network Open.
Researchers analyzed data from the Children’s Respiratory and Environmental Workgroup, which includes children and their families from urban, suburban, and rural environments in the United States.
Participants, whose birth years ranged from 1987 to 2007, were followed up to age 11 years. Daily estimates of PM2.5 and NO2 were obtained from 2000 to 2016. The cohort included 5279 children (51.5% male), of whom 1659 (31.4%) were Black, 835 (15.8%) were Hispanic, 2555 (48.4%) were White, and 229 (4.3%) were characterized by another race or ethnicity.
A Cox proportional hazard model was used to assess the association between exposures and asthma incidence, adjusting for variables such as maternal education and smoking status, the child’s race/ethnicity and sex, and parental asthma history.
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[E]xposure to PM2.5 or NO2 air pollution during early childhood may play a role in the development of childhood asthma, with higher risk among minoritized families living in densely populated communities characterized by fewer opportunities and resources
Among the participants, 1305 children (24.7%) had asthma by age 11 years, and 954 (18.1%) had asthma by age 4 years. PM2.5 was not associated with any neighborhood-level variables, and NO2 was correlated with population density (r=0.63).
Stronger associations were observed with outcomes and pollutants averaged during the first 2 and 3 years of life vs other pollution averages. An increase in 1 interquartile range (IQR) in mean NO2 (6.1 μg/m3) in the first 3 years of life was associated with a higher asthma incidence in the first 4 years of life (hazard ratio [HR], 1.25; 95% CI, 1.03-1.52) and through the first 11 years (HR, 1.22; 95% CI, 1.04-1.44).
In the same 3-year average, a 1-IQR increase in mean PM2.5 (3.4 μg/m3) was associated with a higher incidence of asthma in children younger than 5 years (HR, 1.31; 95% CI, 1.04-1.66) and those younger than 12 years (HR, 1.23; 95% CI, 1.01-1.507). NO2 and PM2.5 had a significant association with increased odds of asthma through age 4 years and age 11 years.
Stronger associations occurred when mothers had less than a high school diploma and in Black children. A significantly greater association was observed between PM2.5 and asthma incidence in Black children younger than 5 years (HR, 1.60; 95% CI, 1.15-2.22) vs White children (HR, 1.17; 95% CI, 0.90-1.52).
Regarding the effect modification of air pollution averaged during the first 3 years of life by neighborhood factors, for an IQR increase in PM2.5, children living in areas with lower education and health and environment opportunity had an increased asthma incidence during the first 4 and 11 years of life. For an IQR increase in NO2, those in areas with a greater proportion of Black residents and in more urban areas had an increased asthma incidence during the first 4 and 11 years of life.
Among several limitations, other pollutants in urban environments such as ozone and other traffic-related air pollution also may contribute to asthma and interact with NO2 and PM2.5, and information on pollution from indoor environments was unavailable.
“These findings suggest that exposure to PM2.5 or NO2 air pollution during early childhood may play a role in the development of childhood asthma, with higher risk among minoritized families living in densely populated communities characterized by fewer opportunities and resources and multiple environmental coexposures,” the study authors concluded.
Disclosure: Some of the study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.
