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Comparative Study
. 2006 Mar 15;173(6):667-72.
doi: 10.1164/rccm.200503-443OC. Epub 2006 Jan 19.

Reduction in fine particulate air pollution and mortality: Extended follow-up of the Harvard Six Cities study

Francine Laden  1 , Joel Schwartz, Frank E Speizer, Douglas W Dockery
Affiliations
Comparative Study

Reduction in fine particulate air pollution and mortality: Extended follow-up of the Harvard Six Cities study

Francine Laden et al. Am J Respir Crit Care Med. .

Abstract

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 microg/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 microg/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.

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Figures

<b>Figure 1.</b>
Figure 1.
Annual average concentrations of PM2.5 in the Harvard Six Cities Study. (Six Cities monitoring data for available years 1980–1988 and PM2.5 estimated from Aerometric Information Retrieval System and extinction data for years where Six Cities data were not available.)
<b>Figure 2.</b>
Figure 2.
Estimated adjusted rate ratios for total mortality and PM2.5 levels in the Six Cities Study by period. P denotes Portage, WI (reference for both periods); T = Topeka, KS; W = Watertown, MA; L = St. Louis, MO; H = Harriman, TN; S = Steubenville, OH. A term for Period 1 (1 if Period 2, 0 if Period 1) was included in the model. Bold letters represent Period 1 (1974–1989) and italicized letters represent Period 2 (1990–1998). In Period 1, PM2.5 (μg/m3) is defined as the mean concentration during 1980–1985, the years where there are monitoring data for all cities (18). In Period 2, PM2.5 is defined as the mean concentrations of the estimated PM2.5 in 1990–1998.
See this image and copyright information in PMC

Comment in

  • A tale of six cities.
    Brunekreef B. Brunekreef B. Am J Respir Crit Care Med. 2006 Mar 15;173(6):581-2. doi: 10.1164/rccm.2601001. Am J Respir Crit Care Med. 2006. PMID: 16522762 No abstract available.
  • Comments on the updated Harvard Six Cities study.
    Gamble JF, Nicolich MJ. Gamble JF, et al. Am J Respir Crit Care Med. 2006 Sep 15;174(6):722; author reply 722-4. doi: 10.1164/ajrccm.174.6.722. Am J Respir Crit Care Med. 2006. PMID: 16959922 No abstract available.

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