Fine particulate matter and incident coronary heart disease in the REGARDS cohort

Abstract

Chronic exposure to fine particulate matter (PM_2.5) is accepted as a causal risk factor for coronary heart disease (CHD). However, most of the evidence for this hypothesis is based upon cohort studies in whites, comprised of either only males or females who live in urban areas. It is possible that many estimates of the effect of chronic exposure to PM_2.5 on risk for CHD do not generalize to more diverse samples.

Methods: Therefore, we estimated the relationship between chronic exposure to PM_2.5 and risk for CHD in among participants in the REasons for Geographic And Racial Differences in Stroke (REGARDS) cohort who were free from CHD at baseline (n=17,126). REGARDS is a sample of whites and blacks of both genders living across the continental United States. We fit Cox proportional hazards models for time to CHD to estimate the hazard ratio for baseline 1-year mean PM_2.5 exposure, adjusting for environmental variables, demographics, and other risk factors for CHD including the Framingham Risk Score.

Results: The hazard ratio (95% CI) for a 2.7-μg/m³ increase (interquartile range) 1-year mean concentration of PM_2.5 was 0.94 (0.83-1.06) for combined CHD death and nonfatal MI, 1.13 (0.92-1.40) for CHD death, and 0.85 (0.73-0.99) for nonfatal MI. We also did not find evidence that these associations depended upon overall CHD risk factor burden.

Conclusions: Our results do not provide strong evidence for an association between PM_2.5 and incident CHD in a heterogeneous cohort, and we conclude that the effects of chronic exposure to fine particulate matter on CHD require further evaluation.

Figure 1

Event rates and 95% confidence intervals of incident coronary heart disease (CHD) by baseline 1-year mean PM_2.5 concentration and baseline risk factor burden for CHD in REGARDS sample

Figure 2. Predicted log hazard for incident total CHD, CHD death, and nonfatal MI versus previous 1-year mean ambient PM_2.5 concentration

Grey bands are 95% prediction intervals. In models that included an interaction between PM_2.5 and risk factor burden, the interaction was not statistically significant for total CHD (p = 0.44), for CHD death (p = 0.47), nor for nonfatal MI (p = 0.09). In models for total CHD, sensitivity analyses did not identify statistically significant interactions between PM_2.5 exposure and gender (p = 0.998), race (p = 0.85), or urbanicity (p = 0.40). None of these interactions were significant for either CHD death or nonfatal MI (data not shown).