Abstract
BackgroundLong-term exposure to air pollution is a hypothesized risk factor for ischemic stroke. In a large case-control study with a complete study base, we investigated whether hospital admissions for ischemic stroke were associated with residential concentrations of outdoor NOx, as a proxy for exposure to air pollution, in the region of Scania, Southern Sweden.MethodsWe used a two-phase case-control study design, including as first-phase controls all individuals born between 1923 and 1965 and residing in Scania in 2002 (N = 556 912). We defined first-phase cases as first-time ischemic stroke patients residing in Scania and registered in the Swedish stroke register between 2001 and 2005 (N = 4 904) and second-phase cases as cases for whom we had information on smoking status, diabetes, and medication for hypertension (N = 4 375). For the controls, information on these covariables was collected from a public health survey, resulting in 4 716 second-phase controls. With a geographical information system and an emission database, individual residential outdoor annual mean NOx concentration was modelled. The data were analyzed with logistic regression.ResultsWe found no evident association between NOx and ischemic stroke. For example, the odds ratio for ischemic stroke associated with the NOx category 20–30 μg/m3 compared to the reference category of <10 μg/m3 was 0.95 (95% CI 0.86–1.06).ConclusionIn this study area, with generally low levels of air pollution, using a complete study base, high-quality ascertainment of cases, and individually modelled exposure, we did not observe any clear association between NOx and ischemic stroke hospital admissions.
Highlights
Long-term exposure to air pollution is a hypothesized risk factor for ischemic stroke
Evidence has been presented that high levels of air pollution have trigger effects on ischemic stroke mortality, [3] and on hospital admissions for ischemic stroke, [4,5] other studies have been negative.[6]
One study found moderate short-term association between low levels of air pollution and hospital admissions for all cerebrovascular diseases, but no association was found for cerebral ischemic diseases.[8]
Summary
Long-term exposure to air pollution is a hypothesized risk factor for ischemic stroke. In a large case-control study with a complete study base, we investigated whether hospital admissions for ischemic stroke were associated with residential concentrations of outdoor NOx, as a proxy for exposure to air pollution, in the region of Scania, Southern Sweden. BMC Public Health 2009, 9:301 http://www.biomedcentral.com/1471-2458/9/301 ischemic stroke.[7] One study found moderate short-term association between low levels of air pollution and hospital admissions for all cerebrovascular diseases, but no association was found for cerebral ischemic diseases.[8]. There have been considerably fewer studies on long-term effects of air pollution on ischemic stroke risk than studies on short-term effects. The studies on long-term exposure to air pollution and stroke have not differentiated ischemic stroke from other cerebrovascular events
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