Association Between Traffic Count and Cardiovascular Mortality: A Prospective Cohort Study in Taiwan

Background: Exposure to traffic-related pollution is positively associated with cardiovascular diseases (CVD), but little is known about how different sources of traffic pollution (eg, gasoline-powered cars, diesel-engine vehicles) contribute to CVD. Therefore, we evaluated the association between exposure to different types of engine exhaust and CVD mortality. Methods: We recruited 12,098 participants from REVEAL-HBV cohort in Taiwan. The CVD mortality in 2000–2014 was ascertained by the Taiwan Death Certificates. Traffic pollution sources (2005–2013) were based on information provided by the Directorate General of Highway in 2005. Exposure to PM2.5 was based on a land-use regression model. We applied Cox proportional hazard models to assess the association of traffic vehicle exposure and CVD mortality. A causal mediation analysis was applied to evaluate the mediation effect of PM2.5 on the relationship between traffic and CVD mortality. Results: A total of 382 CVD mortalities were identified from 2000 to 2014. We found participants exposed to higher volumes of small car and truck exhausts had an increased CVD mortality. The adjusted hazard ratio (HR) was 1.10 for small cars (95% confidence interval [CI], 0.94–1.27; P-value = 0.23) and 1.24 for truck (95% CI, 1.03–1.51; P-value = 0.03) per one unit increment of the logarithm scale. The findings were still robust with further adjustment for different types of vehicles. A causal mediation analysis revealed PM2.5 had an over 60% mediation effect on traffic-CVD association. Conclusions: Exposure to exhaust from trucks or gasoline-powered cars is positively associated with CVD mortality, and air pollution may play a role in this association.