How Air Pollution Affects the Heart and Lungs: Evidence from the California Teachers Study

Study in one sentence

In a large cohort of California women, long-term exposure to fine particulate matter (PM_2.5) and nitrogen dioxide (NO₂) was associated with increased incidence of cardiovascular and respiratory diseases, including heart attacks, stroke, and pneumonia, even at pollution levels below current regulatory standards.

Publication and date

The study, titled “Long-Term Exposure to Air Pollution and Cardiorespiratory Disease in the California Teachers Study Cohort,” was published in the American Journal of Respiratory and Critical Care Medicine (AJRCCM) on October 1, 2011. The authors are Michael J. Lipsett, Bart D. Ostro, Peggy Reynolds, Debbie Goldberg, Andrew Hertz, Michael Jerrett, Daniel F. Smith, Cynthia Garcia, Ellen T. Chang, and Leslie Bernstein. AJRCCM is a peer-reviewed medical journal.

Research question

The researchers aimed to investigate whether long-term exposure to ambient air pollutants—specifically fine particulate matter (PM_2.5), nitrogen dioxide (NO₂), and ozone (O₃)—was associated with the incidence of cardiovascular and respiratory diseases in a large cohort of women. They also sought to determine if any observed associations persisted at pollution concentrations below the current U.S. Environmental Protection Agency (EPA) standards.

Method

The study used data from the California Teachers Study (CTS), a prospective cohort of 133,479 female teachers and school administrators established in 1995–1996. For this analysis, 73,711 women who lived in California at baseline and had no prior history of the outcomes of interest were followed through 2005. Residential addresses were updated throughout follow-up, and monthly average air pollution exposures were estimated using a geostatistical model that combined data from government monitoring stations with land-use characteristics. The pollutants examined were PM_2.5, NO₂, and O₃. Health outcomes—including coronary heart disease (CHD), stroke, and pneumonia—were identified through linkage with statewide hospitalization data. The researchers used Cox proportional hazards models to estimate hazard ratios (HRs) for each outcome per interquartile range (IQR) increase in pollutant concentration, adjusting for a wide range of individual-level covariates such as age, race, smoking, body mass index, physical activity, diet, and socioeconomic status.

Main findings

For PM_2.5, each IQR increase of 5.8 μg/m³ was associated with a 20% higher risk of coronary heart disease (HR 1.20, 95% CI 1.02–1.41) and a 19% higher risk of stroke (HR 1.19, 95% CI 0.97–1.46), though the latter was of borderline statistical significance. For NO₂, an IQR increase of 9.2 ppb was associated with a 12% higher risk of CHD (HR 1.12, 95% CI 1.00–1.26) and a 15% higher risk of stroke (HR 1.15, 95% CI 0.99–1.33). For pneumonia, PM_2.5 showed a 34% increased risk (HR 1.34, 95% CI 1.10–1.64) per IQR, and NO₂ a 21% increase (HR 1.21, 95% CI 1.04–1.41). Ozone was not consistently associated with any of the outcomes. Importantly, the associations for PM_2.5 and NO₂ remained when the analysis was restricted to areas where pollutant concentrations were below the current EPA annual standards (15 μg/m³ for PM_2.5 and 53 ppb for NO₂), suggesting that there may be no safe threshold for these pollutants.

What the findings do not prove

The study does not prove that air pollution causes heart or lung disease. As an observational cohort study, it can only identify associations, not establish causation. The findings cannot rule out the possibility that unmeasured confounding factors—such as occupational exposures, noise pollution, or residual socioeconomic gradients—explain part of the observed relationships. Additionally, the study does not demonstrate that reducing air pollution would immediately lower disease risk, nor does it identify the specific biological mechanisms responsible for the associations.

Limitations

The study has several limitations. The cohort consisted entirely of female teachers and administrators in California, which may limit generalizability to men, other occupations, or populations in different geographic regions. Air pollution exposure was estimated at the residential address level and did not account for indoor air quality, time spent away from home, or personal mobility. The use of hospitalization data may miss milder cases not requiring hospital admission. Although many confounders were adjusted for, residual confounding remains possible. The study also did not examine short-term exposure effects or the impact of pollutant mixtures beyond the three pollutants studied.

How it compares with previous research

These findings are consistent with a growing body of epidemiological evidence linking long-term air pollution exposure to cardiovascular and respiratory morbidity. Earlier landmark studies, such as the Harvard Six Cities Study and the American Cancer Society’s Cancer Prevention Study II, had reported associations between PM_2.5 and cardiovascular mortality. The CTS study extends this work by demonstrating similar associations for nonfatal incident events and for respiratory outcomes like pneumonia, and by showing effects at concentrations below current regulatory standards. The results also align with more recent multi-city and multi-cohort analyses that have found no evidence of a threshold for PM_2.5-related health effects.

Why it matters

This study provides important evidence that air pollution, even at levels commonly found in many parts of the United States, may contribute to the development of serious heart and lung diseases. It supports the case for tightening air quality standards to protect public health and suggests that current regulations may not be sufficient. For individuals, the findings underscore the potential benefits of reducing personal exposure to air pollution, though the study does not evaluate specific interventions. For policymakers and researchers, it highlights the need for continued monitoring and further investigation into the mechanisms and full health impacts of air pollution.

Link to the primary paper

Lipsett MJ, Ostro BD, Reynolds P, Goldberg D, Hertz A, Jerrett M, Smith DF, Garcia C, Chang ET, Bernstein L. Long-term exposure to air pollution and cardiorespiratory disease in the California Teachers Study cohort. Am J Respir Crit Care Med. 2011 Oct 1;184(7):828-35. doi: 10.1164/rccm.201012-2082OC.