Air pollution and childhood asthma in Iceland – Results from a low-pollution area

Background No studies have investigated associations between air pollution and childhood asthma in Iceland. We aimed to explore if air pollution during pregnancy and early life was associated with asthma hospitalisations and medication use in Icelandic children. Methods We included all singleton births in Iceland from 2005 to 2018 (n = 59,355). Residential air pollution exposure during pregnancy and first three years of life was analysed in relation to asthma hospitalisations (International Classification of Diseases ICD J45–J46) and medication use (Anatomical Therapeutic Chemical classification ATC R03A–R03D), using Cox regression with age as time scale and adjusting for maternal, offspring, and household factors. Findings Asthma hospitalisation occurred in 3.9% of children, and 18.6% had asthma medication prescriptions after age 3. Mean annual exposures to fine and course particulate matter (PM_2.5 and PM₁₀) and nitrogen dioxide (NO₂) were low, but 26%, 1%, and 37%, respectively, was exposed to pollution exceeding World Health Organization (WHO) guidelines. All pollutants except ozone increased asthma hospitalisation risk (hazard ratios 1.08 to 1.59 per interquartile range (IQR) increase, lower 95% confidence intervals (95% CIs) ranging from 0.97 to 1.24 and upper 95% CIs from 1.17 to 2.04) with PM_2.5 exhibiting the highest risk (HR 1.59, 95% CI 1.24–2.04). Associations during pregnancy and early life were similar. Risk estimates for asthma medication use were lower than for hospitalisations. Nevertheless, pregnancy exposures to primary organic aerosols (POA), secondary organic aerosols (SOA), sulphate (SO₄^2-), sulphur dioxide (SO₂), secondary inorganic aerosols (SIA), PM_2.5 and PM₁₀ were significantly associated with increased asthma medication use. Interpretation Air pollution exposure even at low levels was associated with increased risk of childhood asthma hospitalisation and medication use in Iceland. PM_2.5 was the most important factor. Our findings highlight the need for continued efforts to further reduce pollution exposure.