Individual and neighborhood socioeconomic status, long term exposure to air pollution and risk of cardiovascular disease in the Women's Health Initiative Observational Study

Abstract

<bold>Background</bold>: Previous studies have reported a positive association between exposure to higher levels of air pollution and cardiovascular mortality and morbidity. However, uncertainty remains regarding the potential confounding and effect modification of this association by socioeconomic status (SES). This study examined the roles that individual and neighborhood SES (at the Census tract level, NSES) may play in the association between particles less than 2.5 μm in aerodynamic diameter (PM_2.5) and incident cardiovascular disease. <bold>Methods</bold>: We studied 48,067 women from the Women's Health Initiative Observational Study (WHI OS) who were free of cardiovascular disease at baseline. Outcomes of interest were time to first cardiovascular event and time to death from cardiovascular cause. Exposure data were obtained from nationwide monitors to predict annual average PM_2.5 concentrations at each subject's baseline geocoded address. Cox-proportional hazards regression was used. All models were adjusted for age, race, smoking, body mass index, diabetes, hypertension, hypercholesterolemia, systolic blood pressure, and physical activity. Individual and neighborhood SES were further adjusted for as covariates or modeled as linear interactions. <bold>Results</bold>: A total of 2,446 cardiovascular events and 536 cardiovascular deaths were observed. In our fully adjusted models, each 10 μg/m<super>3</super> higher PM_2.5 exposure was associated with a 1.22 times higher hazard (95% CI, 1.06 to 1.40) for cardiovascular events and a 1.31 times higher hazard (95% CI, 0.95 to 1.81) for cardiovascular deaths. In this cohort, neither individual nor neighborhood SES characteristics were strong confounders and individual SES characteristics also did not modify these associations. Only the following neighborhood SES variables: median family income, percent of adults over 25 years with high school degree, median home value, and the NSES score (a measure of overall deprivation of a neighborhood) were found to be significant effect modifiers. Greater effects tended to be observed among those residing in more disadvantaged neighborhoods. <bold>Conclusions</bold>: Long term exposure to PM_2.5 was associated with increased risk of cardiovascular disease among a cohort of postmenopausal women and this effect cannot be explained by confounding by individual or neighborhood SES. In this cohort, women living in more disadvantaged neighborhoods were disproportionately affected by the adverse effects of PM_2.5 exposure on cardiovascular health. These results add to previously published research that tend to show greater effects among the less advantaged groups. Thus, a focus to reduce risks in these susceptible populations may be germane to public health and environmental policy.