Now, major findings by the University of Louisville’s Green Heart Louisville Project show that if more trees were added to city neighborhoods than currently exist, significant health benefits would improve for residents. The study, for the first time, found that residents in neighborhoods where tree and shrub density more than doubled had lower levels of a key blood marker indicative of inflammation relative to residents living outside these greened zones. This reduction in inflammation is important because generalized inflammation is known to be one of the major risk factors for heart disease and other chronic diseases.
The Green Heart Louisville Project was initiated in 2018 by the Christina Lee Brown Environment Institute at the University of Louisville, in partnership with The Nature Conservancy, Washington University in St. Louis, Hyphae Design Laboratory, and numerous other partners, to test the hypothesis that the presence of urban greening is associated with better heart health. Thus, the unusually close design of the study to that of useful clinical trials on medical treatments lends its results to be especially sound.
Eventually, over 8,000 large trees and shrubs were planted across selected neighborhoods in a four-square-mile area in South Louisville. The selected neighborhoods were Taylor-Berry, Jacobs, Hazelwood, Oakdale, Wilder Park, and Beechmont. The residents in these sampled neighborhoods were the treated population, and immediate surrounding neighborhoods where new plantings did not take place consisted of the control group. In that respect, the authors compared health data between the two groups to assess the effect of increased greenery.
Data were initially collected through blood, urine, hair, and nail sampling of 745 residents and through thorough measurement of tree coverage and air pollution levels. This baseline data provided an overview of the health status of the community before tree planting started. The researchers later checked again on the health of the residents and found that individuals living in the areas where plants had been placed showed much lower hs-CRP—13-20% as a yardstick for general inflammation. High levels of hs-CRP are very strongly linked to increased rates of cardiovascular diseases, such as heart attacks, and are a much more powerful predictor of heart attacks than cholesterol levels. The researchers also propose a higher risk for diabetes and certain cancers.
The decrease in hs-CRP reported by the study translated to about a 10-15% decrease in the risk of heart attack, cancer, or death from any cause. “This gives us one of the clearest indications so far of how something as seemingly mundane as the number of trees on a street could have a tangible impact on people’s health.”
The Green Heart Louisville Project is significant because it’s one of the first studies that have shown proof an intentional increase in neighborhood greenery may result in improved health outcomes. While several other studies have suggested a correlation between residence in green areas and a reduction in health issues, this provides actual data that increasing tree cover in urban settings can directly decrease health risks. Success within the project has not gone unnoticed. The Green Heart Louisville Project received an additional $4.6 million in August from the National Institute of Environmental Health Sciences to extend the study an additional five years. This latest funding grows a preliminary $3 million grant given by the NIEHS, placing investment in the project at more than $8 million. Coupled with that, The Nature Conservancy donated over $8.7 million in project management, tree planting, and maintenance, amongst others. The local donors added to this total figure more than $3 million; that was how broad-based support was advanced for this pioneering research.
The project has entailed planting 8,425 evergreen tree species and shrubs from species such as pine, cypress, yew, holly, and magnolia, plus 630 deciduous trees mainly from dogwood, oak, and serviceberry. These trees were planted on different dates over the years 2019 to 2022 and are maintained by team members on the project, in association with BrightView Landscape, for their continued survival and benefit.
High-sensitivity C-reactive protein (hs-CRP) was the primary biomarker used in the measurement of the health effects of intervention from tree plantings. Levels of hsCRP usually increase by age, and the detected reduction in hsCRP in this study was associated with the effect between a 42-year-old and a 33-year-old. This is also similar to the difference observed in reductions between persons who had regular exercise compared to those who did not.
This finding was presented on August 26th at the International Society for Environmental Epidemiology’s 36th Annual Conference, held in Santiago, Chile, by Daniel Riggs, PhD, assistant professor of Environmental Medicine at the University of Louisville. More research is underway with the hope that additional greenery in urban areas will become a standard approach to improving health.
As the link of greening of cities with health is increasingly understood, the Green Heart Louisville Project serves as the first landmark on how alteration in the environment improves health in very substantial ways. This could further give way to new projects within other cities, thereby helping residents lead a better lifestyle if this project receives more research and support.
Source: UofL Flickr