The benefits of green space have long been hypothesized as wide-ranging. Now a new study homes in on how green living may benefit your health at the very heart of things.

You already associate the term "leafy greens" with health, because you know that dietary fiber (a.k.a. roughage) does a body good. But there's another kind of leafy green that a new study shows is good for your heart: trees, parks, greenbelts, and other residential foliage. It seems that the more you've got in your neighborhood, the lower your risk of cardiovascular disease.

Over a five-year period, researchers tracked the heart health of over 400 outpatients from the University of Louisville's cardiology clinic in an effort to determine whether living in areas of high "residential greenness" correlated with improved patient progress.

According to the authors of the study, which was published in December in the Journal of the American Heart Association, while the results were consistent with previous research "suggest[ing] that green surroundings support cardiovascular health by decreasing exposure to air pollution and encouraging physical activity, while others have found a link between residential proximity to greenness and better mental health [...] our results suggest that the beneficial effects of greenness may be attributable, at least in part, to a favorable neurohormonal profile [...]. These findings are consistent with the results of previous studies showing that residential greenness is inversely associated with stress, anxiety, and mood disorders [...]."1

Tests conducted over the five-year study period showed that participants living in greener surroundings had lower urinary levels of epinephrine, an indication of lower stress; lower urinary levels of F2-isoprostane, an indication of less oxidative stress on cells; a better angiogenic profile, meaning a higher capacity to repair blood vessels and faster wound healing. "This relationship was independent of sex, race, age, smoking status, neighborhood deprivation index, statin use, and roadway exposure," say the authors, who chose not to exclude smokers on the basis of "previous evidence suggest[ing] that smokers may be particularly sensitive to environmental influences."

The study results highlight a well-known fact about racial inequality in the United States: because of economic disadvantages, African-Americans have less opportunity to benefit from green spaces. "[P]articipants residing in areas of low greenness were more likely to live in a deprived area and have significantly lower median household income," the authors note. As a result, "Black participants were more likely to reside in areas with lower greenness" than their white counterparts.

According to Dr. Aruni Bhatnagar, the study's lead author, "[I]ncreasing the amount of vegetation in a neighborhood may be an unrecognized environmental influence on cardiovascular health and a potentially significant public health intervention. [...] Although the mechanisms underlying the beneficial vascular effects of greenness remain obscure, these observations support the notion that exposure to green spaces could have salutary effects on cardiovascular health."

In an effort to better understanding the relation between green spaces and heart health, Bhatnagar is at the head of the Green Heart Project, a new five-year study that is said to be "the first controlled experiment to test urban greening in the same way a new pharmaceutical intervention is tested."

Announced in October 2017, researchers assessed the risk of diabetes and heart disease, stress levels, and the strength of social ties for 700 residents of a predetermined South Louisville area. Then this fall the team⎯a collaboration between University of Louisville collaboration with the Nature Conservancy, Hyphae Design Laboratory, and the Institute for Healthy Air Water and Soil⎯began planting 8,000 trees, plants and shrubs throughout the area "to create an urban ecosystem that promotes physical activity while decreasing noise, stress and air pollution." Over the next three years, the residents will receive annual check-ups to evaluate whether and how the increased greenery has affected their physical health, mental well-being, and social ties.

“No one knows whether and to what extent trees and neighborhood greenery affects human health and why,” Bhatnagar said in late 2017, a little over a year before the publication of his group's recent study. “This work will tell us exactly how to design a neighborhood that supports human health and could provide protection from everything from asthma to heart disease to dementia.”

The aim of the Green Heart Project is to generate results that "will inform a new municipal decision-making process, one that prioritizes health." And although it will be another three years before all of the data is in, a simple truth is clear: green is good. Whether you're eating it or living within it, for your heart and the rest of you, the more green you have in your life, the healthier you'll be.