Abstract
IntroductionAir quality is a major environmental determinant of health. Environmental greenness – a measure of vegetative presence – has been associated with reduced risk of cardiovascular disease. However, the impact of greenness on the relationship between air pollution and cardiovascular disease (CVD) has been less studied.HypothesisEnvironmental greenness is associated with reduced total CVD mortality and mediates some of the relationship between air pollution and CVD mortality.MethodsThe Centers for Disease Control and Prevention Interactive Atlas of Heart Disease provided national CVD death rates, Environmental Protection Agency air quality measurements (particulate matter PM2.5), and Census sociodemographic information (age, race, education, and income) by county across the United States. These data were matched to mean county normalized difference vegetation index (NDVI) derived from National Aeronautics and Space Administration (NASA) Moderate Resolution Imaging Spectroradiometer (MODIS) 250 m spatial resolution data. Linear regression modeling estimated the relationship between air pollution and greenness on CVD mortality using SAS version 9.4 software. Mediation analysis of greenness on the relationship between air pollution and CVD mortality was then conducted.ResultsAmbient concentration of PM2.5 ranged from 3 to 19.7 μg/m3 with a mean of 9 μg/m3 ± 1.9 μg/m3 and NDVI ranged from 0.00 to 0.80 with mean of 0.41 ± 0.13. For every 0.1-unit increase in NDVI, CVD mortality decreased by 13.2 deaths per 100,000 adults (p = 0.0001). For every 1 μg/m3 increase in PM2.5, CVD mortality increased by 38.8 deaths per 100,000 adults (p < 0.0001). Mediation analysis suggests that NDVI is a statistically significant mediator of the PM2.5 to CVD mortality relationship, with NDVI explaining 4.3% of this relationship (p=0.0009).ConclusionsOur analysis of air quality, environmental greenness, and CVD death rates demonstrates that greenness is independently associated with reduced CVD morality and also mediates the relationship between air pollution and CVD mortality. The evidence suggests that environmental interventions to increase greenness and reduce air pollution may reduce excess cardiovascular mortality.
