When air pollution in a city declines, the city benefits with a directly proportional drop in death rates, a new study has found.
Well, the Dockery and company published a seminal set of articles on the 6 city study back in the 90s that are the gold standard of air pollution epidemiology. It takes large long-term studies like these to establish even tenuous correlations, and their graphs connecting particle concentrations and mortality were beautiful straight lines.
This follow up is pretty cool because the cities had made most of the reductions in the 70s and 80s after the passage of the Clean Air Act and this study clearly demonstrates that the bar for lowering mortality/cancer rates by lowering fine particle levels has not been reached yet. The abstract of the paper is below the fold.
Reduction in Fine Particulate Air Pollution and Mortality
Extended Follow-up of the Harvard Six Cities Study
Am. J. Respir. Crit. Care Med. 2006; 173: 667-672
Francine Laden, Joel Schwartz, Frank E. Speizer and Douglas W. Dockery Exposure, Epidemiology, and Risk Program, Department of Environmental Health, Harvard School of Public Health; and Channing Laboratory, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, Massachusetts
Rationale: A large body of epidemiologic literature has found an association of increased fine particulate air pollution (PM2.5) with acute and chronic mortality. The effect of improvements in particle exposure is less clear.
Objectives: Earlier analysis of the Harvard Six Cities adult cohort study showed an association between long-term ambient PM2.5 and mortality between enrollment in the mid-1970s and follow-up until 1990. We extended mortality follow-up for 8 yr in a period of reduced air pollution concentrations.
Methods: Annual city-specific PM2.5 concentrations were measured between 1979 and 1988, and estimated for later years from publicly available data. Exposure was defined as (1) city-specific mean PM2.5 during the two follow-up periods, (2) mean PM2.5 in the first period and change between these periods, (3) overall mean PM2.5 across the entire follow-up, and (4) year-specific mean PM2.5. Mortality rate ratios were estimated with Cox proportional hazards regression controlling for individual risk factors.
Measurements and Main Results: We found an increase in overall mortality associated with each 10 µg/m3 increase in PM2.5 modeled either as the overall mean (rate ratio [RR], 1.16; 95% confidence interval [CI], 1.07–1.26) or as exposure in the year of death (RR, 1.14; 95% CI, 1.06–1.22). PM2.5 exposure was associated with lung cancer (RR, 1.27; 95% CI, 0.96–1.69) and cardiovascular deaths (RR, 1.28; 95% CI, 1.13–1.44). Improved overall mortality was associated with decreased mean PM2.5 (10 µg/m3) between periods (RR, 0.73; 95% CI, 0.57–0.95).
Conclusion: Total, cardiovascular, and lung cancer mortality were each positively associated with ambient PM2.5 concentrations. Reduced PM2.5 concentrations were associated with reduced mortality risk.
Key Words: air pollution • cohort studies • follow-up studies • mortality