Long-term Exposure to Particulate matter and cardiovascular disease in South Korea: investigating multi-level interaction with individual- and area-level factors

Abstract

Background and aim: It has been well known that individuals or groups are not equally vulnerable to air pollution. However, few studies have investigated whether individual susceptibility to air pollution varies across different community environments. This study aimed to estimate the effects of long-term PM₁₀ exposure on cardiovascular disease (CVD) in South Korea and to examine whether individual status of underlying disease and area-level medical infrastructure modify the effect. Methods: The study population comprised 392,104 subjects from the National Health Insurance Service-National Sample Cohort (2006-2015) residing in 120 districts in South Korea. The CVD event was defined as the first occurrence of a hospital visit or admission from 2006 to 2015. Time‐varying Cox proportional-hazards models were used to estimate the association between five-year moving averages of PM₁₀ and CVD events. Effect modifications by the individual status of underlying disease (cancer, diabetes, and hypertension) were determined by two-way interaction, stratifying by area-level medical index (calculated with the number of hospitals, hospital beds, and medical personnel). Results: Long-term exposure to PM₁₀ was positively associated with the risk of CVD events (HR per 10 μg/m³, 1.04; 95% CI, 1.02-1.06). In areas with a low medical index, PM₁₀‐associated CVD risks were higher among those with cancer (HR 1.19; 95% CI, 1.00-1.42) as compared to those without (HR, 1.07; 95% CI, 1.02-1.12). In areas with a low medical index, subjects with cancer showed a lower risk of CVD associated with PM₁₀ than those without. Conclusions: This study suggests that the individual-level status of an underlying disease and area-level medical infrastructure could be interrelated in determining the health effect of PM₁₀. Consideration of this multi-level interaction in population vulnerability to air pollution can help understand the complex mechanisms by which air pollution creates health disparities. Keywords: Particulate matter, cardiovascular disease, effect modification, underlying disease, medical infrastructure