Associations of acute exposure to fine and coarse particulate matter and mortality among older people in Tokyo, Japan

Recent studies have reported adverse health effects of short-term exposure to coarse particles independent of particulate matter less than 2.5μm in diameter (PM_2.5), but evidence in Asian countries is limited. We therefore evaluated associations between short-term exposure to particulate matter (PM) and mortality among older people in Tokyo, Japan. We used a time-stratified, case-crossover design. Study participants included 664,509 older people (≥65years old) in the 23 urbanized wards of the Tokyo Metropolitan Government, who died between January 2002 and December 2013. We obtained PM_2.5 and suspended particulate matter (SPM; PM<7μm in diameter) from one general monitoring station. We calculated PM_7-2.5 by subtracting PM_2.5 from SPM to account for coarse particles. We then used conditional logistic regression to estimate odds ratios (ORs) and 95 confidence intervals (CIs). Same-day PM_2.5 and PM_7-2.5 were independently associated with all-cause and cause-specific mortality related to cardiovascular and respiratory diseases; for example, both pollutants were positively associated with increased risk of all-cause mortality even after simultaneous adjustment for each pollutant: OR of 1.006 (95% CI: 1.003, 1.009) for PM_2.5 and 1.016 (95% CI: 1.011, 1.022) for PM_7-2.5. Even below concentrations stipulated by the Japanese air quality guidelines for PM_2.5 and SPM (PM₇), we observed adverse health effects. This study provides further evidence that acute exposure to PM_2.5 and coarse particles is associated with increased risk of mortality among older people. Rigorous evaluation of air quality guidelines for daily average PM_2.5 and larger particles should be continued.