Long-term fine particulate matter exposure and cardiovascular mortality in the general population: a nationwide cohort study

Background: Although eastern Asian countries are exposed to high levels of air pollution, the impact of long-term exposures to fine particulate matter (PM_2.5) air pollution on all-cause and cardiovascular mortality is not well identified. We assessed the relationship between long-term PM_2.5 exposure and all-cause/cardiovascular mortalities.

Methods: We included 436,933 subjects who received national health examinations from the Korean National Health Insurance Service-based National Sample Cohort. We matched subjects' residential-address areas with hourly-measurements of PM_2.5 concentration data. We estimated the risk of mortality with average PM_2.5 exposure during the study period using a Cox proportional-hazards model.

Results: During 1,683,271 person·years, all-cause and cardiovascular mortalities were observed in 6432 and 1603 subjects (382 and 95 per 100,000 person·years, respectively). An increase in 10 μg/m³ in PM_2.5 was associated with increases in all-cause and cardiovascular mortalities by 3.4 % [2.7-4.1] and 4.7 % [3.6-5.8], respectively (each p < 0.001). PM_2.5 was linearly and significantly correlated with these all-cause and cardiovascular mortalities above 18 μg/m³ of PM_2.5 (p < 0.001), but it was not significant below 18 μg/m³ of PM_2.5. To investigate the specific PM_2.5 concentration for raising cardiovascular mortality more, we analyzed the sensitivities/specificities for different PM_2.5 levels, and 18 μg/m³ showed the highest Youden's index (sensitivity + specificity-1) with c-index of 0.85 (0.84-0.86). PM_2.5 effect on all-cause mortality was more profound in subjects with previous myocardial infarction compared to the opposite population.

Conclusions: In the Korean general population exposed to high-air pollution, long-term PM_2.5 exposure was linearly associated with increased risk for all-cause and cardiovascular mortality, especially above 18 μg/m³ of PM_2.5.