Air pollution exposure associated with asthma, wheezing development in children

Children exposed to higher levels of air pollution are at an increased risk for developing asthma and persistent wheeze compared with those who are not exposed, according to a study published in The BMJ.

“We determined whether asthma onset and persistent wheezing was associated with family-related factors, whether high levels of air pollution in the children’s residential area was associated with an increased risk of asthma and persistent wheezing and whether associations of air pollution with asthma and persistent wheezing vary by family related factors,” Gitte J. Holst, MD, a postdoctoral scholar in the section of environment, occupation and health at Aarhus University, Denmark, and colleagues wrote.

Researchers conducted a nationwide case-control study of 3,192,785 Danish children born from 1997 to 2014. Participants were followed for asthma and persistent wheezing development from age 1 to 15 years. Exposure to air pollution assessment was obtained from a Danish air pollution modeling system, and data on parental asthma were obtained from the Danish National Patient Register. Researchers assessed maternal smoking status in the first meeting during pregnancy, parental education from the education register and parental income from the income register.

Children of parents with asthma (adjusted HR = 2.29; 95% CI, 2.22-2.35) and children with mothers who smoked during pregnancy (aHR = 1.2; 95% CI, 1.18-1.22) had a higher incidence of asthma. Children of parents with high educational attainment (aHR = 0.72; 95% CI, 0.69-0.75) and higher incomes (aHR = 0.85; 95% CI, 0.81-0.89) had a lower incidence of asthma.

Exposure to particulate matter 2.5 g or less (HR per 5 g/m³ = 1.05; 95% CI, 1.03-1.07) 10 g or less (HR per 5 g/m³ = 1.04; 95% CI, 1.02-1.06) and nitrogen dioxide (HR per 5 g/m³ = 1.04; 95% CI, 1.03-1.04) was associated with an increased risk for asthma and persistent wheezing.

The positive association of particulate matter 2.5 g or less remained consistent across different models.

“The findings from this study strengthen the evidence that parental asthma, parental education and maternal smoking during pregnancy are risk factors for asthma onset and persistent wheezing in children. Moreover, we found that children exposed to high levels of [particulate matter 2.5 g or less] were more likely to develop asthma and to have persistent wheezing,” the researchers wrote. “These findings therefore support emerging evidence that exposure to air pollution might influence the development of asthma. This finding needs to be substantiated in future studies.”