1 Center of Epidemiology and Screening, Department of Public Health, Faculty of Health and Medical Sciences, Københavns Universitet2 Department of Public Health, Faculty of Health and Medical Sciences, Københavns Universitet3 Diet, Genes and Environment, Danish Cancer Society Research Centre, Copenhagen, Denmark.4 Department of Neurology, Aalborg Hospital, Aarhus University Hospital, Aalborg, Denmark.5 Department of Environmental Science, Aarhus University, Roskilde, Denmark.6 Department of Public Health, Section for Epidemiology, Aarhus University, Aarhus, Denmark; Department of Cardiology, Aalborg University Hospital, Aalborg, Denmark.7 Center of Epidemiology and Screening, Department of Public Health, Faculty of Health and Medical Sciences, Københavns Universitet
Exposure to road traffic noise and air pollution have both been associated with risk for stroke. The few studies including both exposures show inconsistent results. We aimed to investigate potential mutual confounding and combined effects between road traffic noise and air pollution in association with risk for stroke. In a population-based cohort of 57,053 people aged 50-64 years at enrollment, we identified 1999 incident stroke cases in national registries, followed by validation through medical records. Mean follow-up time was 11.2 years. Present and historical residential addresses from 1987 to 2009 were identified in national registers and road traffic noise and air pollution were modeled for all addresses. Analyses were done using Cox regression. A higher mean annual exposure at time of diagnosis of 10µg/m(3) nitrogen dioxide (NO2) and 10dB road traffic noise at the residential address was associated with ischemic stroke with incidence rate ratios (IRR) of 1.11 (95% CI: 1.03, 1.20) and 1.16 (95% CI: 1.07, 1.24), respectively, in single exposure models. In two-exposure models road traffic noise (IRR: 1.15) and not NO2 (IRR: 1.02) was associated with ischemic stroke. The strongest association was found for combination of high noise and high NO2 (IRR=1.28; 95% CI=1.09-1.52). Fatal stroke was positively associated with air pollution and not with traffic noise. In conclusion, in mutually adjusted models road traffic noise and not air pollution was associated ischemic stroke, while only air pollution affected risk for fatal strokes. There were indications of combined effects.