‘Source-specific’ air pollution and risk of stroke in Denmark

BackgroundLong-term air pollution is a risk factor for stroke. Which types and sources of air pollution contribute most to stroke in populations is unknown. We investigated whether risk of stroke differed by type and source of air pollution.MethodsWe selected all persons aged >50 years and living in Denmark in the period 2005–17. We estimated running 5-year mean residential air-pollution concentrations of particulate matter ResultsThe cohort numbered 2 million people and 94 256 cases of stroke. Interquartile ranges (IQR) of air pollution were associated with risk of stroke with HRs of 1.077 (95% CI: 1.061–1.094, IQR: 1.85 µg/m3) for PM2.5, 1.039 (1.026–1.052, IQR: 4248 particles/cm3) for UFP, 1.009 (1.001–1.018, IQR: 0.28 µg/m3) for EC and 1.028 (1.017–1.040, IQR: 7.15 µg/m3) for NO2. Traffic sources contributed little to the total exposure. HRs associated with air pollution from traffic were close to the null, whereas non-traffic sources tended to be associated with HRs higher than those for total air pollution, e.g. for non-traffic PM2.5, the HR was 1.091 (1.074–1.108).ConclusionsAir pollution, including UFP, was associated with risk of stroke. The risk appeared attributable mainly to air pollution from non-traffic sources.