Investigating the Regional Concentrations-Response Relations between PM2.5 and daily mortality in Japan

Abstract

BACKGROUND: The concentration-response (CR) functions of PM2.5 are sensitive to various local factors, such as meteorological conditions, PM sources and components, and population sensitivity to PM. However, the shape of local CR functions remains unclear in many regions in Japan. This research investigates the association between PM2.5 and cause-, age-, and location-specific mortality to identify susceptible subpopulations and regions using a nationwide dataset. METHODS: A two-stage analysis was performed to quantify the associations of PM2.5 with mortality. In the first stage, regional differences in the effects of PM were investigated. A time-series quasi-Poisson model, combined with a distributed lag non-linear model and a flexible functional form of splines, was applied to evaluate the location-specific associations between PM2.5 and mortality. Various covariates were controlled, including weather variables, day of the week, and seasonal and long-term time trends. Stratified analyses were performed by age groups and death cause categories. We used a random-effects meta-analytic model to estimate the pooled cumulative association in the second stage. Potential reasons for the regional heterogeneity of PM2.5 effects were further explored through random-effects meta-regression analyses, separately carried out for multiple variables as meta-predictors. RESULTS: Geographic variations in the concentration of PM2.5 were observed in Japan. An increase in PM2.5 concentration was associated with an increase in excess risk of mortality, and the magnitude of the corresponding associations appeared to vary by region in Japan. CONCLUSIONS: The regional risks of premature mortality from exposure to PM2.5 were investigated. We identified vulnerable regions and susceptible subpopulations. The disparity in the association of mortality risks and PM2.5 was apparent between geographical regions, indicating the importance of developing area-specific strategies and local risk prevention plans that can serve as a basis for policymaking to reduce the corresponding health effects.