The study referenced at the Scientific Sessions used national air quality greenness, cardiovascular disease, and census data from 2014-2015. Greenness was measured by individual counties across the United States, which was compared to national disease death rates from the Centers for Disease Control and Prevention’s Interactive Atlas of Heart Disease. Data was also overlaid from the Environmental Protection Agency’s air quality measurements of particulate matter for each county and the Census Bureau’s information on age, race, education, and income by county.
The study found that for every 0.10 unit increase in greenness, deaths from heart disease decreased by 13 deaths per 100,000 adults. For every one microgram increase in particulate matter per cubic meter of air, death from heart disease increased by roughly 39 deaths per 100,000 adults.
William Aitken, M.D. explains, “We found that areas with better air quality have higher greenness, and that having higher greenness measures, in turn, is related to having a lower rate of deaths from heart disease.”
“Given the potential cardiovascular benefits of higher greenness measures, it’s important that dialogue about improved health and quality of life include environmental policies that support increasing greenness. Policymakers should support greenness through efforts that promote environmental justice through equitable access to green spaces, clean air and clean water, as well as minimizing exposure to environmental hazards,” he added.
NASA Imaging to Measure Greenness
For the purpose of this study, greenness was categorized as a measure of vegetative presence, including trees, shrubs, and grass, which is often assessed by NASA imaging of the Earth and other methods. Researchers used the Normalized Difference Vegetative Index (NDVI) to measure wavelengths of visible and near-infrared sunlight reflected from the Earth’s surface via NASA satellite imagery. Using this method, researchers were able to find that a higher index meant more healthy vegetation, as chlorophyll typically absorbs visible light and reflects near-infrared light.
By using these methods of study, a relationship between greenness and risk of heart disease death was confirmed. Researchers hope that these results will encourage environmental interventions, such as tree planting, to increase vegetation and greenness. They plan to perform a future longitudinal study in Miami to assess if changes in neighborhood greenness over time are associated with changes in cardiovascular disease.