Research Projects

Project at a Glance

Title: Extended analyses of air pollution and cardiovascular disease in the California Teachers Study cohort

Principal Investigator / Author(s): Michael Lipsett, M.D.

Contractor: Department of Health Services

Contract Number: 06-336


Research Program Area: Health & Exposure

Topic Areas: Health Effects of Air Pollution, Vulnerable Populations


Abstract:

Several studies have reported associations between long-term exposure to air pollution and mortality. A number of important questions remain, however, regarding the impact of how long-term exposure is measured, the existence of critical windows of exposure, the relative importance of various constituents of particulate matter, the relationship of chronic exposure to new cases (incidence) of disease, and the shape of the concentration-response function linking fine particulate matter with mortality. In an extension of previous work, we developed estimates of long-term air pollution exposure at the residences of over 100,000 female participants in the longitudinal California Teachers Study (CTS). We examined associations between several exposure metrics and the following outcomes: all-cause mortality, cause-specific mortality (principally diseases of the cardiovascular and respiratory systems), as well as new cases (incidence) of both fatal and non-fatal heart attacks and stroke. To derive the pollutant exposure metrics, we linked the CTS participantsí addresses with monthly estimates of long-term exposure to particulate matter less than 2.5 microns in diameter (PM2.5), particulate matter less than 10 microns in diameter (PM10), ozone, carbon monoxide (CO), nitrogen dioxide (NO2), nitrogen oxides (NOx), and sulfur dioxide (SO2). The main analyses examined potential relationships of mortality and disease incidence with long-term residential exposures to PM10, ozone, CO, NO2, NOx, and SO2 from 1996 through 2005, and to PM2.5 beginning in 1999, when the latter pollutant began to be systematically measured statewide. Participantsí addresses were linked as well with several cross-sectional measures of potential traffic-related exposures from the year 2000. We analyzed these relationships while adjusting for many individual-level and neighborhood variables, and undertook a variety of sensitivity analyses. We found elevated risks between long-term exposure to PM2.5 and mortality from ischemic heart disease as well as incidence of stroke, particularly among women who were post-menopausal at baseline. Long-term exposures to PM10, ozone and NOx were associated with elevated risks of ischemic heart disease mortality. PM10 exposure was also linked with incident stroke. The association of ozone with mortality was most likely due to its strong correlations with PM10 and PM2.5. Among never-smokers, NOx exposure was associated with elevated risks of cardiovascular and ischemic heart disease mortality. We did not find that women who had diabetes or who were overweight or obese were at increased risk of PM2.5-associated effects. Traffic density, a measure of the estimated number of vehicle miles traveled within 150 m of a participantís residence, was associated with all-cause, cardiopulmonary and cardiovascular mortality. In additional analyses of associations between long-term exposure to PM2.5 and mortality, we found that: (i) the exposure-response relationship was best described as linear; and (ii) significant effect estimates were evident by one year of exposure, with the magnitude of the association leveling off with increasing duration. This study provides additional evidence that long-term exposure to air pollution is associated with mortality from heart disease, and demonstrates as well that exposure to particulate matter is associated with the incidence of new cases of stroke.


 

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