Improving air pollution exposure estimates in the analysis of mortality in the California Teachers Study cohort
Hundreds of studies implicate exposure to short-term ambient air pollution as a risk factor for exacerbation of pre-existing illness and for mortality in susceptible individuals. In contrast, much less is known about the health consequences associated with long-term exposures to air pollution and traffic. The effects associated with long-term exposure play an important role in determining annual ambient air quality standards and are a major factor in the calculation of health and economic benefits associated with air quality improvements. While few studies have examined relationships between long-term exposures and mortality, all have found positive associations with at least one pollutant metric; however, the results are not entirely consistent. In addition, significant uncertainties remain among these studies regarding the appropriate assumptions for exposure assessment.
Researchers from the California Department of Health Services, the Office of Environmental Health Hazard Assessment, and the University of Southern California have embarked on an ARB-funded investigation of the California Teachers Study (CTS), a prospective examination of the disease and mortality experience of over 100,000 current and former female public school teachers and administrators. Many members of this study population are at risk for developing and dying from cardiopulmonary diseases by virtue of their older age and post-menopausal status. We have conducted preliminary analyses of the relationships of long-term exposure to ozone on total and cardiopulmonary mortality.
This follow-up study is designed to examine the following research questions: (1) What time period and duration of exposure (e.g., the most recent month or year, aggregation of the most recent three years, exposure from five to 10 years ago, and so forth) have the strongest associations with cardiopulmonary mortality? (2) What are the relative contributions of shorter-term versus longer-term exposures? (3) What are the impacts of varying distance assumptions when assigning exposures from fixed-site monitors or from GIS-generated traffic metrics? (4) What impacts, if any, do these alternative exposure metrics have on risk estimates for other outcomes not examined in the initial effort, such as cancer and nonmalignant respiratory disease? (5) Are associations altered when examining only never-smokers? (6) How are the effect estimates affected by alternative risk models that incorporate additional determinants of mortality, including ecological covariates? (7) Can any particularly susceptible subgroups be identified through stratified analysis? (8) What do flexible modeling techniques, such as nonparametric smoothing, suggest regarding the shape(s) of the exposure-response functions?
Principal Investigators: Peggy Reynolds, Ph.D.
Funding: California Air Resources Board (ARB) |
