Air Pollution and Family Related Determinants of Asthma Onset and Persistent Wheezing in Children: Nationwide Case-Control Study

Abstract

To identify risk factors (air pollution and family related) for the onset of asthma and persistent wheezing in children.All Danish children born from 1997 to 2014 who were managed for asthma onset and persistent wheezing from the age of 1 year to 15 years by using a national registry based, matched case-control design.Children were managed in the Danish National Patient Register for the classification of asthma or persistent wheezing after hospital discharge, or with a minimum of 2 prescriptions for asthma medications. Information regarding concentration of air pollutants (several gases, aerosols, particular matter <2.5µm [PM2.5] and particular matter <10µm), parental asthma diagnoses and asthma medication prescriptions, maternal smoking habits, highest completed parental education, and parental income levels were collected and analyzed for hazard ratios (HRs).From 1997–2014, 3 192 785 children were included in the study, and 122 842 (3.84%) children developed asthma and/or persistent wheezing, with a mean age of development of 1.9 years. Maternal asthma had a higher risk than paternal asthma (adjusted HR): 1.72 (95% CI: 1.72 to 1.77) vs 1.51 (95% CI: 1.48 to 1.53)], but having 2 parents with asthma was associated with a 2.40-fold (2.34-fold to 2.47-fold) risk of childhood asthma. Maternal smoking during pregnancy (adjusted HR: 1.23 [1.18 to 1.28]) or quitting during pregnancy (HR: 1.20 [1.18 to 1.22]) increased the risk of childhood asthma. Exposures to PM2.5, particular matter <10µm, and nitrogen dioxide were also associated with development of asthma, with PM2.5 exposure being the most consistent. Higher parental income levels, together and independently, had a reduced risk for childhood asthma (adjusted HR: 0.85 [95% CI: 0.81 to 0.89) for the highest parental income level, compared with 1.04 (95% CI: 1.00 to 1.08) for the lowest parental income level]. Higher parental education levels, together and independently, had a reduced risk for childhood asthma (adjusted HR: 0.72 [95% CI: 0.69 to 0.75]) for the highest parental education level, compared with 0.98 [95% CI: 0.95 to 1.00] for the lowest parental education level).Parental history of asthma, higher levels of exposure to PM2.5, and maternal smoking during pregnancy all increase a child’s risk of developing asthma and persistent wheezing. High levels of parental educational attainment and income are associated with a lower risk of developing asthma and persistent wheezing in children.Strengths of this study include the use of a large database that covered 18 years. In this study, researchers did not analyze atopy, lung function, or inflammatory markers. A family history of asthma, tobacco exposure and environmental pollutants were confirmed as risk factors for asthma development. Smoking cessation campaigns and environmental strategies to decrease particulate matter exposure may reduce the number of children who develop asthma.