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. 2012 Jul;120(7):965-70.
doi: 10.1289/ehp.1104660. Epub 2012 Mar 28.

Chronic exposure to fine particles and mortality: an extended follow-up of the Harvard Six Cities study from 1974 to 2009

Johanna Lepeule  1 , Francine Laden, Douglas Dockery, Joel Schwartz
Affiliations

Chronic exposure to fine particles and mortality: an extended follow-up of the Harvard Six Cities study from 1974 to 2009

Johanna Lepeule et al. Environ Health Perspect. 2012 Jul.

Abstract

Background: Epidemiologic studies have reported associations between fine particles (aerodynamic diameter ≤ 2.5 µm; PM2.5) and mortality. However, concerns have been raised regarding the sensitivity of the results to model specifications, lower exposures, and averaging time.

Objective: We addressed these issues using 11 additional years of follow-up of the Harvard Six Cities study, incorporating recent lower exposures.

Methods: We replicated the previously applied Cox regression, and examined different time lags, the shape of the concentration-response relationship using penalized splines, and changes in the slope of the relation over time. We then conducted Poisson survival analysis with time-varying effects for smoking, sex, and education.

Results: Since 2001, average PM2.5 levels, for all six cities, were < 18 µg/m3. Each increase in PM2.5 (10 µg/m3) was associated with an adjusted increased risk of all-cause mortality (PM2.5 average on previous year) of 14% [95% confidence interval (CI): 7, 22], and with 26% (95% CI: 14, 40) and 37% (95% CI: 7, 75) increases in cardiovascular and lung-cancer mortality (PM2.5 average of three previous years), respectively. The concentration-response relationship was linear down to PM2.5 concentrations of 8 µg/m3. Mortality rate ratios for PM2.5 fluctuated over time, but without clear trends despite a substantial drop in the sulfate fraction. Poisson models produced similar results.

Conclusions: These results suggest that further public policy efforts that reduce fine particulate matter air pollution are likely to have continuing public health benefits.

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Conflict of interest statement

The authors declare they have no actual or potential competing financial interests.

Received 25 October 2011; accepted 28 March 2012.

Figures

Figure 1
Figure 1
Annual mean PM2.5 levels during 1974–2009 in the Harvard Six Cities study.
Figure 2
Figure 2
Survival probabilities under three hypothetical scenarios: participants of the Harvard Six Cities study are exposed to 10, 15, or 20 µg/m3 PM2.5 during the entire follow-up period of 1974–2009.
See this image and copyright information in PMC

Comment in

  • Is ambient PM2.5 sulfate harmful?
    Grahame T, Schlesinger R. Grahame T, et al. Environ Health Perspect. 2012 Dec;120(12):A454; author reply A454-5. doi: 10.1289/ehp.1205873R. Environ Health Perspect. 2012. PMID: 23211380 Free PMC article. No abstract available.

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