Long-term exposure to elemental constituents of particulate matter and cardiovascular mortality in 19 European cohorts: Results from the ESCAPE and TRANSPHORM projects
Introduction
Recent studies of health effects of particulate matter (PM) show accumulating evidence of adverse effects on cardiovascular (CVD) mortality (Brook et al., 2010, Hoek et al., 2013). However, effect estimates of long-term exposure to PM2.5 and PM10 (particles < 2.5 μm and 10 μm in aerodynamic diameter) varied among different studies and geographical locations, showing elevated risks in some cities and areas in Europe and the United States (Cesaroni et al., 2013, Laden et al., 2006, Lepeule et al., 2012, Lipsett et al., 2011, Pope et al., 2002) but no or little association in others (Beelen et al., 2008, Puett et al., 2011).
Ambient PM2.5 and PM10 represent a heterogeneous mixture of constituents from diverse sources e.g. fossil fuel combustion, biomass burning and human activity (Kelly and Fussell, 2012). However, little is known about which PM constituents are associated with higher risks. Several studies showed evidence of acute effects of PM components on CVD mortality, but results varied among studies (Cao et al., 2012, Ito et al., 2011, Valdes et al., 2012, Zhou et al., 2011). In the large national study of United States, only nickel (Ni) and vanadium (V) were associated with CVD mortality (Bell et al., 2009). The reasons for these differences are not clear but may include methodological differences, chance findings as well as true variations related to PM composition and/or population susceptibility. Long-term effects of specific elemental components on CVD mortality have only been examined by a single study in the U.S. which suggested that cardiopulmonary mortality was associated significantly with PM2.5 (HR: 1.11, 95% CI: 1.03–1.21), sulfate (HR: 1.14, 95% CI: 1.01–1.29), nitrate (HR: 1.11, 95% CI: 1.03–1.19) and silicon (HR: 1.05, 95% CI: 1.00–1.10) (Ostro et al., 2010, Ostro et al., 2011). Toxicological studies have identified several transition metals (copper, iron, vanadium, nickel, and zinc) that are likely to promote inflammation and oxidative stress (Gerlofs-Nijland et al., 2007, Happo et al., 2008, Happo et al., 2010).
A recent study within ESCAPE (European Study of Cohorts for Air Pollution Effects) reported overall no statistically significant associations between long-term exposure to PM mass (PM2.5, PM10) and cardiovascular mortality averaged over 19 ongoing cohorts in Europe (Beelen et al., accepted for publication). The magnitude of the association differed across cohorts and we hypothesized that some of the difference in effect estimates could be due to well-documented differences in particle composition in the study areas (De Hoogh et al., 2013). De Hoogh et al. (2013) documented that the correlation between particle mass and several elements was moderate to low, suggesting that the null effect for PM mass may hide effects for some components. Furthermore for some elements (e.g. V and Ni) the major source (shipping, residual oil combustion) was present only in a few of the study areas. Therefore, more specific examinations are needed taking individual particle components into account.
The aim of this paper was to investigate effects of long term exposure to PM constituents on CVD mortality within the ESCAPE (European Study of Cohorts for Air Pollution Effects) and TRANSPHORM (Transport related Air Pollution and Health impacts — Integrated Methodologies for Assessing Particulate Matter) projects. Standardized methods for exposure assessment, confounder and endpoint definition and statistical analysis were applied to 19 ongoing cohort studies.
Section snippets
Methods
The association between PM constituents and cardiovascular mortality was analyzed in each cohort separately using a common statistical protocol for exposure assessment, outcome definition, confounder models and statistical analysis. Methods followed the ESCAPE analysis protocol described in previous papers (Beelen et al., accepted for publication, Beelen et al., in press, Raaschou-Nielsen et al., 2013). Cohort-specific results were evaluated and pooled using meta-analysis at the coordinating
Characteristics of the study population
The entire study population consisted of 322,291 participants contributing 4,551,184 person years at risk (average time of follow-up 14.1 years), with 9545 CVD deaths during follow-up (Table 1). Cohorts were recruited mostly in the 1990s. Cohorts differed in the number of participants, the mean baseline age, and availability of data on confounders (Table 2 and Tables C.1–C.19 in Appendix C). Age gender, smoking status, and area-level SES were available for all cohorts. Smoking intensity and
Discussion
This study found no statistically significant associations between a comprehensive set of elemental constituents of PM and overall cardiovascular mortality based on 19 European cohorts. Most of the combined hazard ratios were close to unity, with exception for PM2.5 Si and S in PM2.5 and PM10.
The strengths of this study include: 1) the use of a large population of 19 study cohorts from 12 countries with a relatively long follow-up history and with detailed individual-level information; 2) the
Acknowledgement
The research leading to these results has received funding from the European Community's Seventh Framework Program (FP7/2007–2011): ESCAPE 3 (grant agreement number: 211250) and TRANSPHORM (ENV.2009.1.2.2.1). SAPALDIA received support in mortality record linkage from the Swiss National Cohort Study, grant numbers: Periode 1.7.2006–30.6.2011: 108806, Periode 1.7.2011–30.6.2014: 134273. The KORA research platform and the MONICA Augsburg studies were initiated and financed by the Helmholtz Zentrum
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