As a doctor and conservationist, I have a natural curiosity about nature and about health. Last month I traveled to Louisville, Kentucky for a groundbreaking announcement on how inextricably intertwined the two are. And why that's important to you and me.
Though many of us intuitively understand that spending time in nature is good for us, there has been a lack of rigorous scientific research to prove it -- until now.
On a sunny day in late August, we gathered at the University of Louisville to share the results of painstaking research that first began back in 2017. The clinical investigation, designed in partnership with the National Institute of Environmental Health Sciences, set out to answer the question, can trees improve our health? The answer, I discovered is: yes. In fact, based on what I learned that day, we might even consider trees as medicine!
Thanks to the Green Heart Louisville Project, the science now confirms that increasing trees in a neighborhood can yield measurable health benefits for residents.
This project set out to test this hypothesis through a collaboration of universities and local leaders, with the financial and advisory support of The Nature Conservancy (TNC), on whose Global Board I sit. I first learned of the research when my wife Tracy and I were seated next to Dr. Aruni Bhatnagar, head of the University of Louisville's Christina Lee Brown Envirome Institute and principal investigator on this unique project, at a TNC dinner in 2018. I remember thinking, can daily exposure to trees strategically placed in a community actually change blood chemistries of the body?
Here's how the intervention of tree and shrub planting worked and what was found.
The Green Heart Louisville Project is the first longitudinal clinical trial to test a "greening intervention" in the same way a new pharmaceutical intervention is tested. Trees are the medicine. This study is groundbreaking because while other studies have found an association or correlation between nature and well-being, the Green Heart Louisville Project is the first to scientifically and quantitatively measure the impact that an increase in trees and shrubs in a neighborhood can have on human health.
After years of data collection and analysis, the Green Heart Project is building a scientific case for the powerful connections between the health of our planet and the health of all of us.
So what was the groundwork for this intervention? It began as a partnership with The Nature Conservancy, Washington University in St. Louis, Hyphae Design Laboratory, and others, under the visionary leadership of the University of Louisville's Aruni Bhatnagar, Ph.D. It was launched as a first-of-its-kind project in 2017 to study whether, and to what extent, living among greener surroundings contributes to better health. The National Institute for Environmental Health Sciences awarded the University Louisville funding to support the research. The Nature Conservancy raised substantial money for the trees, and dedicated expertise to the planning, implementation, and maintenance of the greening effort.
Key to the success of the effort was philanthropist Christina Brown, whom the Kentucky branch of The Nature Conservancy dubbed the "Godmother of Kentucky." Christy, a longtime friend to my wife Tracy and me, has dedicated her life to advancing health, nature, and sustainability in all the communities she touches. The interconnecting influences that comprise health and wellbeing are captured in the illustrative emblem of "The Circle of Health and Harmony," (see figure) closely associated with her many endeavors and proudly worn as a lapel pin by so many advocates around the country. This tool emphasizes how environmental health is central to all well-being. It was Christy's commitment that provided the inspiration and foundational funding for the Christina Lee Brown Envirome Institute, whose mission is to investigate all aspects of health and their interrelationships, and it was her support that laid the groundwork for the Green Heart Project to come to fruition.
With this robust backing, the project began with baseline health data collection from over 750 study participants. The Nature Conservancy led several contractors and nonprofit partners, including Louisville Grows, on a multi-year effort to plant more than 8,000 trees and shrubs - most of them evergreens - in designated intervention areas in four neighborhoods in South Louisville. The work focuses on neighborhoods that had fewer trees compared with more affluent parts of the city. The neighborhoods are mixed racially and ethnically: 54 percent White, 29 percent Black, and 11 percent Hispanic. A busy highway runs directly through the neighborhoods -- providing an unhealthy baseline of air pollution. The comparison control areas of these neighborhoods did not receive trees from the project.
Project team members maintained the trees after planting to promote their survival, growth, and impact. Picture these South Louisville neighborhoods being gradually hugged by a growing mix of pines, hollies, arborvitaes, magnolias, dogwoods, oaks, and more.
Nearly seven years since the official launch of the Green Heart Louisville Project and nearly two years since tree planting concluded, the first phase of clinical study results are in - and they are promising.
How a "Greening Intervention" Improved Individual and Public Health
The researchers found that participants living in the neighborhoods of the greening intervention had, post-planting, lower levels of a widely recognized blood marker of inflammation (C-reactive protein) strongly associated with risk for cardiovascular disease, as well as diabetes and some cancers.
The precise etiology of this dramatic reduction of blood inflammatory measures is yet to be determined. Hypotheses currently being investigated include the degrees to which trees filter air pollution that could harden coronary arteries, whether trees improve sleep and reduce stress by buffering ambient roadway noise, how efficiently various species of trees absorb harmful pollutants, and what chemicals are released by trees that physiologically lower stress hormone levels.
Why is this significant? Because it means that adding trees to a neighborhood may reduce community members' risk of heart disease and other chronic, costly, and fatal diseases. The study demonstrated a significant decrease in the inflammatory blood marker. The clinical manifestations and direct impact on the heart, lungs, and other organs will be measured in the next phase of study.
Heart disease is the leading cause of death in the U.S. and globally. And in Louisville alone, heart disease costs the city an estimated $650 million a year. If we could re-direct even a small amount of those costs towards prevention through a prescription of trees, it would reduce healthcare costs significantly over the long term. And save lives.
The Nature Conservancy raised and invested $8.7 million for this project and played a fundamental role in implementing the greening efforts. TNC, the largest conservation entity in the nation, is committed to applying scientific research at the intersection of conservation and human health. TNC is grounded in the belief that human health is intrinsically and intimately tied to the health of our planet.
In addition to improving the body's health, we already know that trees reduce heat, provide wildlife and pollinator habitat, decrease stormwater runoff, increase property values, and lower utility bills. Psychologists have observed that stress levels and depressive states are less in greener sections of urban areas.
Indeed, when viewed in its totality, no pill or medicine provides as many ancillary benefits as does nature.
The Green Heart Louisville Project should give us hope, because it is a scientifically tested, replicable model for investing in nature in cities in the U.S. and around the world. It's a biological and economic reason to proactively bring nature to the cities. When I share this exciting news with others, they frequently ask what they can do as individuals. My answer is:
First, help spread the word. We live in an era of information overload, and even critical research and findings fail to get the attention they deserve. People should know about these important findings because they have such a demonstrable impact on our individual health and well-being.
Second, I encourage others to become engaged and advocate for investments in nature with elected officials and other decision makers. The recently enacted Inflation Reduction Act makes substantial monies available to local communities for planting of trees. Most community leaders are not aware of this resource for better health.
Nature is essential infrastructure, too often taken for granted. But now we know it can make us healthier. Our local, state, and federal budgets need to reflect the reality that our environment and the nature around us affect our health in tangible, economically beneficial ways.
Thanks to the dedicated efforts of all those who contributed to the Green Heart Louisville Project, we now have a proven reason to advocate for increasing trees and green spaces in cities as a key strategy to improve individual and community health - while also making our cities cooler, more beautiful, and more welcoming places to live in and raise our families.