Early air pollution exposure may heighten childhood asthma risk
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Key takeaways:
- Researchers found a link between childhood asthma risk and early PM2.5 and nitrogen dioxide pollution exposure.
- Race and maternal education changed the strength of this link.
A high risk for asthma in children was linked to increased levels of fine particulate matter and nitrogen dioxide exposure in the first 3 years of life, according to results published in JAMA Network Open.
“Where you live, the urban environment and the resources in your community influence a child’s risk of asthma,” Antonella Zanobetti, PhD, principal research scientist of environmental health at Harvard T.H. Chan School of Public Health, told Healio.
Previous research has shown that improvement in the neighborhood environment such as traffic exposures can improve asthma control, she said.
“Clinicians can ask parents about local traffic patterns near their homes and on the way to school; this is relevant from both a physical safety and a lung health point of view,” Zanobetti continued.
Also, she said, physicians can inquire about other neighborhood stressors that may be linked to population density and asthma risk.
“Awareness of risk factors is a first step towards imagining risk reduction, though much of risk reduction may need to occur on a community-level rather than a patient/family-level basis,” she said.
Using eight cohorts from the Children’s Respiratory and Environmental Workgroup consortium, Zanobetti and colleagues assessed 5,279 children (51.5% boys) in the U.S. to determine how fine particulate matter (PM2.5) and nitrogen dioxide exposure during the first 3 years of life impact the risk for asthma in early childhood (< 5 years old) and middle childhood (< 12 years old).
During this analysis, researchers accounted for several factors: maternal education, parental asthma, smoking during pregnancy, child’s race and ethnicity, sex, neighborhood characteristics and cohort.
Main findings
The total cohort included high percentages of white children (48.4%) and Black children (31.4%), with fewer Hispanic children (15.8%) and children not labeled as Hispanic, non-Hispanic Black or non-Hispanic white (4.3%).
Within the study population, physician-diagnosed asthma was more prevalent at 11 years old vs. at 4 years old (24.7% vs. 18.1%), according to researchers.
In children aged younger than 5 years, the risk for asthma rose as the interquartile range of nitrogen dioxide (6.1 g/m3) pollution increased within the first 3 years of life (HR = 1.25 per 1 interquartile range increase; 95% CI, 1.03-1.52).
Researchers observed a similar elevated risk for asthma in children aged younger than 12 years exposed to levels of nitrogen dioxide above the mean value during the first 3 years of life (HR = 1.22 per 1 interquartile range increase; 95% CI, 1.04-1.44).
In terms of PM2.5, the risk for asthma was heightened with exposure to this pollutant above the interquartile range (3.4 g/m3) early on in life in both children aged younger than 5 years (HR = 1.31 per 1 interquartile range increase; 95% CI, 1.04-1.66) and children aged younger than 12 years (HR = 1.23 per 1 interquartile range increase; 95% CI, 1.01-1.507).
Individual, community characteristics
After dividing the total cohort according to individual-level characteristics, researchers found that the risk for asthma in children through age 4 years linked to early PM2.5 exposure was greater in Black children (HR = 1.6; 95% CI, 1.15-2.22) vs. white children (HR = 1.17; 95% CI, 0.9-1.52), and the same outcome was true in children through age 11 years (Black children, HR = 1.41; 95% CI, 1.06-1.89 vs. white children, HR = 1.15; 95% CI, 0.93-1.43).
Black children through age 11 years also faced a greater risk for asthma with early nitrogen dioxide exposure compared with white children of this age (HR = 1.3; 95% CI, 1.03-1.63 vs. HR = 1.13; 95% CI, 0.9-1.41).
Another individual-level characteristic that changed the strength of the link between childhood asthma risk and pollutant exposure was maternal education. Children born to mothers with no high school education had a higher risk for asthma with exposure to PM2.5 in the first 3 years of life than children born to mothers with a college and graduate school education through age 4 years (HR = 1.46; 95% CI, 0.96-2.2 vs. HR = 1.24; 95% CI< 0.97-1.6) and through age 11 years (HR = 1.39; 95% CI, 0.97-1.99 vs. HR = 1.17; 95% CI, 0.95-1.45).
Researchers noted that the same was true for early-life nitrogen dioxide exposure, with a greater risk for asthma observed in children born to mothers with no high school education vs. a college and graduate school education.
Further, community-level characteristics had an influence on the relationship between asthma risk and early air pollutant exposure, according to researchers.
“We found not only that air pollution may play a role in the development of childhood asthma but also that this risk was higher among minoritized families living in densely populated areas,” Zanobetti said.
Residence in a neighborhood with low vs. high education and health environment opportunities raised the risk for asthma in early and middle childhood linked to early elevated PM2.5 exposure.
In early and middle childhood, the risk for asthma with early elevated nitrogen dioxide exposure was greater among those living in neighborhoods with a high vs. low proportion of Black individuals and a high vs. low population density, according to researchers.
“Future studies when examining the association between air pollution and asthma both in children and adults should consider and understand whether the impact of air pollution on asthma differs not only by individual characteristics such as parental history of asthma and education, but also by community-level factors, as where individuals live, work and play are strongly related to health outcomes,” Zanobetti told Healio.