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The University of Louisville’s Green Heart Louisville Project has found that people living in neighborhoods where the number of trees and shrubs was more than doubled showed lower levels of a blood marker of inflammation than those living outside the planted areas.

General inflammation is an important risk indicator for heart disease and other chronic diseases.

UofL’s Christina Lee Brown Envirome Institute launched the first-of-its-kind project in 2018, to study whether and how living among more densely greened surroundings contributes to better heart health.

The design of the study closely mirrors clinical trials which test whether medical treatments are effective. The team applied the treatment – the addition of large trees and shrubs – to some participants’ neighborhoods but not to others. They then compared residents’ health data to see how the addition of the trees affected their health.

“The Green Heart Louisville Project is an excellent example of how our university’s innovative and collaborative researchers are working to improve lives in our community and far beyond,” UofL President Kim Schatzel said. “Trees are beautiful, but these results show that the trees around us are also beneficial to individual and community health. Through this and many other projects, the Envirome Institute is improving health at the community level, not just for individuals, but for everyone living in a neighborhood.”

Researchers took blood, urine, hair and nail samples and documented health data from 745 people living in a four-square-mile area of south Louisville. The researchers also took detailed measurements of tree coverage and levels of air pollution in the area.

Then, over 8,000 large trees and shrubs were planted in designated project area neighborhoods. Those living in the greened area were considered the treated population and the results obtained from this population were compared with residents of adjacent neighborhoods, where no trees were planted.

After the plantings, researchers found those living in the greened area had 13-20% lower levels of a biomarker of general inflammation called high-sensitivity C-reactive protein (hsCRP) than those in the areas that received no new trees or shrubs. Higher levels of hsCRP are strongly associated with a risk of cardiovascular disease, so the reduction corresponds to nearly 10-15% reduction in the risk of heart attacks and cancer.

The project has received an additional $4.6 million in funding from the National Institute of Environmental Health Sciences to support continued research over the next five years.