Associations of long-term exposure to ambient PM_2.5 with mortality in Chinese adults: A pooled analysis of cohorts in the China-PAR project

Background: The concentration-response relationship between mortality and long-term exposure to fine particulate matter (PM_2.5) has not been fully elucidated, especially at high levels of PM_2.5 concentrations.

Objective: We aimed to evaluate chronic effects of ambient PM_2.5 exposure on deaths among Chinese adults in high-exposure settings.

Methods: Participants of the Prediction for Atherosclerotic cardiovascular disease Risk in China (China-PAR) project were included from four prospective cohorts among Chinese adults aged ≥18 years old. The overall follow-up rate of the four cohorts was 93.4% until the recent follow-up survey that ended in 2015. The average of satellite-based PM_2.5 concentrations during 2000-2015 at 1-km spatial resolution was assigned to each participant according to individual residence addresses. Based on the pooled analysis of individual data from the four cohorts, a Cox proportional hazards model was used to estimate the hazard ratio (HR) and corresponding 95% confidence intervals (95% CIs) for the association of PM_2.5 exposure with mortality after multivariate adjustment.

Results: A total of 116,821 participants were eligible in the final analysis. During a mean of 7.7 years of follow-up, 6,395 non-accidental deaths and 2,507 cardio-metabolic deaths occurred. The mean of PM_2.5 concentration was 64.9 μg/m³ ranging from 31.2 μg/m³ to 97.0 μg/m³. For each 10 μg/m³ increment in PM_2.5, the HR was 1.11 (95% CI: 1.08-1.14) for non-accidental mortality and 1.22 (95% CI: 1.16-1.27) for cardio-metabolic mortality. In addition, a weak exponential curve for the concentration-response association between mortality and PM_2.5 was observed among Chinese adults.

Conclusions: Our study provided important evidence of the long-term effects of PM_2.5 exposure on deaths among Chinese adults. The findings expand our knowledge on concentration-response relationship in high-exposure environments, which is essential to address the urgent challenge of reducing the disease burden attributable to PM_2.5 exposure in rapidly industrializing countries such as China.