Long-term exposure to traffic-related air pollution and the risk of death from hemorrhagic stroke and lung cancer in Shizuoka, Japan

A number of studies have linked exposure to long-term outdoor air pollution with cardiopulmonary disease; however, the evidence for stroke is limited. Furthermore, evidence with the risk for lung cancer (LC) is still inconsistent. We, therefore, evaluated the association between long-term exposure to traffic-related air pollution and cause-specific mortality. Individual data were extracted from participants of an ongoing cohort study in Shizuoka, Japan. A total of 14,001 elderly residents completed questionnaires and were followed from December 1999 to January 2009. Annual individual nitrogen dioxide (NO₂) exposure data, as an index for traffic-related exposure, were modeled using a Land Use Regression model and assigned to the participants. We then estimated the adjusted hazard ratios (HRs) and their confidence intervals (CIs) associated with a 10μg/m³ elevation in NO₂ for all-cause or cause-specific mortality using time-varying Cox proportional hazards models. We found positive associations of NO₂ levels with all-cause (HR=1.12, 95% CI: 1.07-1.18), cardiopulmonary disease (HR=1.22, 95% CI: 1.15-1.30), and LC mortality (HR=1.20, 95% CI: 1.03-1.40). Among cardiopulmonary disease mortality, not only the risk for ischemic heart disease (HR=1.27, 95% CI: 1.11-1.47) but also the risks for stroke were elevated: intracerebral hemorrhage (HR=1.28, 95% CI: 1.05-1.57) and ischemic stroke (HR=1.20, 95% CI: 1.04-1.39). The present study supports the existing evidence that long-term exposure to traffic-related air pollution increases the risk of cardiopulmonary as well as LC mortality, and provides additional evidence for adverse effects on intracerebral hemorrhage as well as ischemic stroke.