Effects of long-term exposure to air pollution on all-cause mortality and cause-specific mortality in seven major cities of South Korea: Korean national health and nutritional examination surveys with mortality follow-up

Abstract

Evidence from cohort studies on the effects of long-term exposure to air pollution on mortality is limited in South Korea, which has high concentration of particles compared to North America, Western Europe, and Japan, and low exposure compared to China. To reduce knowledge gaps between other countries and South Korea, we investigated the association between all-cause, cardiovascular, and respiratory mortality and long-term exposure to PM10 and, as a surrogate for fine particles from local emission sources, SO2 and NO2. Participants comprised 18,220 subjects (97,114.4 person-years) residing in 73 districts of seven major cities of South Korea who were assigned to measurements of fixed-site monitoring stations and followed up. We applied Cox proportional hazard models with time-varying exposure up to three years average of air pollutants. We adjusted for individual and district-level covariates measured at baseline such as age, sex, socioeconomic positions, and health behaviors. We found that hazard ratios of PM10 and SO2 for all-cause mortality leveled off over approximately 5 ppb of SO2 and 35-50 mu g/m(3) of PM10. Interquartile range increases of PM10 (5.05 mu g/m(3)), SO2 (2.09 ppb), and NO2 (11.41 ppb) were associated with 14.4% (95% CI:-0.4, 31.4), 18.1% (-4.5, 46.0), and 18.9% (-8.7, 54.7) increases in cardiovascular mortality, respectively. We did not find positive associations for respiratory mortality. The increase in cardiovascular mortality varied by sex (for PM10, in females, 27.4% (5.8, 53.5) increase), smoking (in non-smokers, 35.9% (12.7, 64.0) increase), drinking (in drinkers, 24.5% (2.1, 51.8) increase), marital status (in those not married, 23.1% (1.1, 49.9)), employment status (for SO2, in those employed, 79.4% (16.1, 177.3) increase), body mass index (in those >= 23, 47.6% (10.4, 97.3) increase), and community deprivation (for PM10, in less deprived communities, 21.0% (1.3, 44.4) increase). In summary, long-term exposure to air pollution is associated with mortality risk in South Korea. Our results suggest that the health effect of long-term exposure to air pollution may not be equal by sex, health behaviors and socioeconomic positions.