Correlation between suspended particles in the environmental air and causes of disease among inhabitants: Cross-sectional studies using the vital statistics and air pollution data in Japan

To identify the diseases that correlate with suspended particle concentration in the ambient air, a cross-sectional epidemiological study was conducted using the annual vital statistics and air pollution estimates of 1881 points throughout Japan. The concentration of suspended particulate matters (SPMs) 10 μm or less in diameter were hypothetically converted to PM2.5 values (converted PM2.5 or cPM2.5) by using a conversion factor obtained from 25 estimates in Japan. Among various causes of death, a significant correlation was observed between both the SPM and cPM2.5 (SPM/cPM2.5) levels and the age-adjusted death rates of ischemic heart disease or hypertensive heart disease in both genders. Correlation was noted with pneumonia, asthma, chronic bronchitis/emphysema, or lung cancer only in females. Unexpectedly, breast, endometrial, and ovarian cancer also showed significant increases in mortality rates related to the SPM/cPM2.5 level, suggesting a role for suspended particles in the ambient air with or without gaseous component as a possible endocrine-disrupting, estrogenic agent. Multivariate regression analysis of confounding factors, smoking rate, population density, and hormone-related factors revealed consistent significance of SPM/cPM2.5 in these diseases.