Abstract
Ambient air pollution has been linked to stroke, but few studies have examined in detail stroke subtypes and confounding by road traffic noise, which was recently associated with stroke. Here we examined the association between long-term exposure to air pollution and incidence of stroke (overall, ischemic, hemorrhagic), adjusting for road traffic noise. In a nationwide Danish Nurse Cohort consisting of 23,423 nurses, recruited in 1993 or 1999, we identified 1,078 incident cases of stroke (944 ischemic and 134 hemorrhagic) up to December 31, 2014, defined as first-ever hospital contact. The full residential address histories since 1970 were obtained for each participant and the annual means of air pollutants (particulate matter with diameter < 2.5 µm and < 10 µm (PM2.5 and PM10), nitrogen dioxide (NO2), nitrogen oxides (NOx)) and road traffic noise were determined using validated models. Time-varying Cox regression models were used to estimate hazard ratios (HR) (95% confidence intervals (CI)) for the associations of one-, three, and 23-year running mean of air pollutants with stroke adjusting for potential confounders and noise. In fully adjusted models, the HRs (95% CI) per interquartile range increase in one-year running mean of PM2.5 and overall, ischemic, and hemorrhagic stroke were 1.12 (1.01–1.25), 1.13 (1.01–1.26), and 1.07 (0.80–1.44), respectively, and remained unchanged after adjustment for noise. Long-term exposure to ambient PM2.5 was associated with the risk of stroke independent of road traffic noise.
Highlights
The objective of this study is to examine the association between long-term exposures to PM2.5, particulate matter (PM) with aerodynamic diameter < 10 μm (PM10), NO2, and nitrogen oxides (NOx) for up to 23 years and incidence of stroke, separately for overall, ischemic and hemorrhagic stroke, while adjusting for road traffic noise
We found no effect modification of the association between ischemic stroke and PM2.5 by noise, smoking status, obesity, hypertension, myocardial infarction, diabetes, physical activity, degree of urbanicity, use of hormone replacement therapy, and work status (SI, Table S7). In this nationwide cohort study of Danish female nurses, we found positive associations between long-term exposure to air pollution and incidence of stroke
Associations were strongest for PM2.5 and ischemic stroke and were not confounded by road traffic noise
Summary
More than 12 million new cases of stroke were reported worldwide in 2017, of which about half died, accounting for approximately 11% of all global deaths. Stroke poses a substantial burden in Denmark with approximately 10,000 new cases each year and 4000 deaths in 2017 corresponding to 7.5% of all deaths. Almost one million stroke deaths globally have been attributed to environmental risk factors in 2017, mainly ambient particulate matter with aerodynamic diameter ≤ 2.5 μm (PM2.5) (GBD 2017 Causes of Death Collaborators 2018; Institute for Health Metrics and Evaluation (IHME, 2019). Association between road traffic noise and stroke has been suggested (Sørensen et al, 2011). Road traffic noise might be a confounder of the association between air pollution and cardio- and cerebrovascular outcomes (Heritier et al, 2019; Sørensen et al, 2014)
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