Long-term exposure to air pollution and risk of adult-onset asthma and COPD: Danish nationwide cohort study
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The question addressed by the study
We investigated the association of long-term exposure to fine particulate matter (PM 2.5 ), black carbon (BC), and nitrogen dioxide (NO 2 ) with incidence of adult-onset asthma and chronic obstructive pulmonary disease (COPD) in a Danish nationwide cohort.
Materials/patients and methods
We followed 3.2 million Danish residents aged 30 years or older on January 1 st , 2000 until December 31 st , 2018, for: (1) incidence of asthma (first hospital contact); (2) incidence of COPD (first hospital contact), and; (3) combined incidence of asthma or COPD (first prescription for obstructive airway disease (OAD) medication). Annual mean concentrations of air pollutants were estimated using European-wide hybrid land-use regression models. Cox proportional hazard models were used to investigate the association of air pollutants with the three outcomes, adjusting directly for age, sex, and socioeconomic status, and indirectly for smoking and body mass index.
Results
Over a mean follow-up of 16 years, 52,648 participants developed asthma, 146,269 developed COPD, and 393,211 were prescribed OAD medication. We found positive, statistically significant associations of PM 2.5 , BC, and NO 2 with all outcomes, strongest for asthma and weakest for OAD medication. The most robust associations were seen for BC in two-pollutant models.
Answer to the question
In a large Danish nationwide analysis, air pollution (PM 2.5 , BC, and NO 2 ) is an important predictor for adult-onset asthma and COPD, with the strongest associations for asthma. Our findings present novel evidence highlighting the relevance of BC as an independent risk factor for asthma and COPD, beyond the effects of PM 2.5 .
What is already known on this topic
Long-term exposure to fine particulate matter (PM 2.5 ) and nitrogen dioxide (NO 2 ) is linked to the increased risk of adultlJonset asthma and COPD, as supported by WHO reviews and meta-analyses of European cohorts. Black carbon (BC), a trafficlJ and combustionlJrelated component of PM 2.5 , is recognized for its toxicological effects on inducing inflammation and oxidative stress in the airway. Still, epidemiological evidence on its role in incident asthma and COPD is scarce and inconclusive, and very few directly contrasted BC and PM 2 .lJ effects in twolJpollutant models.
What this study adds
In a nationwide Danish cohort of >3 million adults with a mean 16 years’ follow-up, long-term exposure to BC showed the strongest, most robust associations with first hospital contact for asthma and COPD, and with first prescriptions for obstructive airway disease medications, even after adjusting for PM 2.5.
How this study might affect research, practice or policy
These results underscore BC as an independent risk factor, supporting its inclusion in air-quality regulations and guiding efforts to target combustion-related pollutants for respiratory disease prevention.
