In a study in the journal Environmental Research, researchers compared blood samples of people participating in the . The researchers found that people living in greener neighborhoods showed immune patterns consistent with lower chronic inflammation, including lower levels of several circulating immune cells linked to inflammatory activity, such as monocytes, natural killer cells, B cells and some white blood cell types.

“The study also found evidence of a shift toward a more regulated immune profile, suggesting that nearby trees and vegetation may do more than improve quality of life – they may also influence the body’s immune system in ways that support cardiovascular health,” said Daniel Riggs, assistant professor in UofL’s and first author of the study. “While the study cannot prove cause and effect, the findings add to growing evidence that greener residential environments may be an important public health resource for reducing inflammation and promoting long-term health.”

The findings provide additional support for preliminary findings from the Green Heart Louisville Project showing that people living in neighborhoods where the number of trees and shrubs was more than doubled had lower levels of a blood biomarker of inflammation than those living outside the planted areas. Those living in the greened area had 13-20% lower levels of high-sensitivity C-reactive protein (hsCRP) than those living in the areas that did not receive additional trees and shrubs. Higher levels of hsCRP are strongly associated with a risk of cardiovascular disease. Higher CRP levels also indicate a higher risk of diabetes and certain cancers.

The recent study evaluated the immune function of Green Heart Louisville Project participants based on the greenness of their residential environment prior to the addition of trees for the project.

“These studies show that greener neighborhoods don’t just look better; they appear to educate our immune system in ways that may reduce chronic inflammation and disease risk,” said Aruni Bhatnagar, director of the Envirome Institute. “They align with the Envirome Institute’s mission of identifying environmental conditions that shape human health and translating those insights into strategies for improving the health of our communities.”

UofL in partnership with The Nature Conservancy, Washington University in St. Louis, Hyphae Design Laboratory and others to study whether and how living among more densely greened surroundings contributes to better heart health.

The Green Heart Louisville Project is a groundbreaking scientific study that is testing the hypothesis that introducing more green trees and shrubs into a neighborhood can directly lower the risk of cardiovascular disease, the leading cause of death worldwide.

“Receiving this award is a great honor not only for our investigators, but also our partners and communities,” said Aruni Bhatnagar, director of the at University of Louisville and project leader for Green Heart Louisville. “It validates years of work which has shown that thoughtfully planned greening can improve cardiovascular and community health, and it affirms that the Green Heart project is not only good science, but also a model for how to improve human health in urban environments. The recognition gives us new momentum to scale this work across Louisville and beyond.”

The Witte-Sakamoto Family Medal in City and Regional Planning was established in 2019 by William Witte, an alumnus of the Weitzman School, and his wife, Keiko Sakamoto to recognize a firm, team or professional for an exemplary plan that advances the field of plan making in at least four of the following areas: social equity, environmental quality, design, public health, mobility, housing affordability and economic development. The juries for the Witte-Sakamoto Family Medal and Prize were chaired by Megan Ryerson, UPS Foundation Chair of Transportation, chair of city and regional planning, and professor of city and regional planning and electrical and systems engineering at Weitzman.

“Green Heart Louisville exemplifies a holistic way of looking at public health – a marriage of design, planning and science to emulate,” said Fritz Steiner, dean and Paley Professor at Weitzman, and a member of the jury who selected Green Heart Louisville for the award.

Launched in 2018 by UofL’s Christina Lee Brown Envirome Institute with support from The Nature Conservancy, the study investigates whether and how living among more densely greened surroundings contributes to better heart health. The Green Heart team applied the treatment – the addition of thousands of mature trees and shrubs – to the center of a four-square-mile area in south Louisville.

The first clinical outcomes from the study, , indicate 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 in the control area. General inflammation is an important risk indicator for heart disease and other chronic diseases.

The Green Heart Project’s work to establish a scientific link between nature – specifically urban greenery – and human health is already influencing projects worldwide. The first clinical outcomes announcement garnered widespread national media attention. Many research papers, posters and talks on the project have been delivered to both scientists and laypeople since the project’s inception, and robust research and outreach for the project continues.

• $2.4 million from the National Institute on Aging will support work by Bradford Hill to investigate how aging leads to reduced blood flow to the heart in older individuals. Hill will study these changes and how this dysfunction could be prevented or corrected. The work may lead to opportunities to prevent age-dependent decline in exercise capacity and promote healthy aging.
• $3.4 million from the National Heart Blood and Lung Institute was awarded for a clinical trial to test whether treatment with the nutritional supplement carnosine improves symptoms and progression in peripheral artery disease in which narrowing of arteries reduces blood flow to arms or legs. Aruni Bhatnagar, Shahid Baba and Amit Dwivedi will conduct the trial.
• $4.67 million from the National Institute of Environmental Health Sciences will support the Green Heart Louisville Project, which studies how an increase in the number of trees and shrubs affects heart health. The team, led by Bhatnagar, recently reported results from their work that began in 2018 in South Louisville. The new award will allow the team to continue to gather data on community health for the next five years as the planted trees continue to grow.
• $ 0.8 million from the Department of Defense was awarded to Daniel Conklin for a two-year project to investigate the role of inhaled agents in Gulf War Illness (GWI), a chronic condition affecting 25-32% of Gulf War veterans. GWI involves chronic pain, muscle fatigue, cognitive impairment, migraines and stroke. Conklin will investigate whether inhalation of volatile organic compounds and particulate matter from burning oil wells, burn pits, contaminated sand and chemical and biological weapons may have led to repeated local and systemic inflammation, causing the condition.

This most recent funding adds to the $11.6 in grants awarded to institute researchers announced earlier this year.

The launched the first-of-its-kind project in 2018 in partnership with The Nature Conservancy, Washington University in St. Louis, Hyphae Design Laboratory and others 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.”

To understand the state of community’s health at the start of the study, 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.

Following this baseline data collection, the Envirome Institute worked with The Nature Conservancy and a host of local partners and contractors to plant more than 8,000 large trees and shrubs in designated neighborhoods within the project area. 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 the project team did not plant any trees.

After the plantings, the research team reassessed residents’ health. They found that those living in the greened area had 13-20% lower levels of a biomarker of general inflammation, a measure called high-sensitivity C-reactive protein (hsCRP) than those living in the areas that did not receive any new trees or shrubs. Higher levels of hsCRP are strongly associated with a risk of cardiovascular disease and are an even stronger indicator of heart attack than cholesterol levels. Higher CRP levels also indicate a higher risk of diabetes and certain cancers.

A reduction of hsCRP by this percentage corresponds to nearly 10-15% reduction in the risk of heart attacks, cancer or dying from any disease.

“These results from the Green Heart Louisville Project indicate that trees contribute more to our lives than beauty and shade. They can improve the health of the people living around them,” said Aruni Bhatnagar, director of the Envirome Institute and UofL professor of medicine. “Although several previous studies have found an association between living in areas of high surrounding greenness and health, this is the first study to show that a deliberate increase in greenness in the neighborhood can improve health. With these results and additional studies that we hope to report soon, we are closer to understanding the impact of local tree cover on residents’ health. This finding will bolster the push to increase urban greenspaces.”

As more is known about the health impacts of increased tree cover, increased greening in cities may emerge as a key method to improve public health.

“Most of us intuitively understand that nature is good for our health. But scientific research testing, verifying and evaluating this connection is rare,” said Katharine Hayhoe, chief scientist of The Nature Conservancy. “These recent findings from the Green Heart Project build the scientific case for the powerful connections between the health of our planet and the health of all of us.”

Earlier in August, the Green Heart Louisville Project was awarded an additional $4.6 million in funding from the National Institute of Environmental Health Sciences to support continued research over the next five years.

These findings were presented by Daniel Riggs, UofL assistant professor of environmental medicine, at the in Santiago, Chile on Aug. 26.

STUDY DETAILS

This study is part of the Green Heart Louisville Project, ongoing research to discover how trees and shrubs affect people’s health.

The neighborhood

The project involved a four-square-mile area of South Louisville straddling the Watterson Expressway, including the Taylor-Berry, Jacobs, Hazelwood, Oakdale, Wilder Park and Beechmont neighborhoods. The project team planted trees and shrubs in a central portion of the project area that included Wyandotte Park, which served as the treated area. They planted no trees in the outer areas of the project area. [SEE MAP]

The people

Researchers enlisted 745 people living in the project area to participate in the project’s ongoing health study. At enrollment, participants were between 25 and 75 years old, 60% female, 77% white and 50% had household income below $50,000 per year. They live in the planted intervention area as well as outside it.

Researchers collected participants’ blood, urine, nail and hair samples and health information before and after planting the trees and shrubs in the “treatment” area.

The trees

Between 2019 and 2022, the Green Heart Project planted 8,425 evergreen trees and shrubs of 42 different species from five different families and 630 deciduous trees. Evergreens were pine, cypress, yew, holly and magnolia. Deciduous trees were mainly dogwood, oak and serviceberry.

Project team members and BrightView Landscape maintain the trees to promote their survival, growth and sustained impact.

The data

High-sensitivity C-reactive protein (hsCRP) is a blood test that measures general inflammation in the body. After the planting, people living in the areas where trees and shrubs were added had 13-20% lower hsCRP levels compared with those living in the areas that did not receive greening from the project.

Inflammation as measured by hsCRP , including stroke, heart attack and coronary artery disease. Previous studies have shown that hsCRP increases with age. The change in hsCRP seen in individuals living in the planted areas was similar to the difference between typical levels in a 42-year-old compared with a 33-year-old.

This difference also is similar to the difference between people who exercise regularly and those who do not. Finally, the decrease in hsCRP levels with planting corresponds to a nearly 10-15% reduction in the risk of heart attacks, cancer or dying from any disease.

Funding

A $3 million grant from the National Institute of Environmental Health Sciences supported the health evaluation of community participants and an additional $4.6 million was recently awarded for continuing this research. These grants bring the total investment by the institute to more than $8 million. The Nature Conservancy provided over $8.7 million in funding to support tree planting and maintenance, project management and other key project needs. The project has had an additional $3 million in support from local donors. Recently, $4.6 million in funding was awarded from the NIEHS for continued research over the next five years.

Collaborators and community partners

Collaborators for this project include the University of Louisville, Washington University in St. Louis, , , the United States Forest Service, and other partners.

Community organizations and resident involvement are vital to the success of this ongoing work to learn the health effects of urban greening. The team is grateful to the residents participating in the health study and those who have allowed tree planting on their property.

Watch a video about the research:

More:

View pictures from the Aug. 27 research results announcement on .

Watch the full Aug. 27 research results announcement on .

A new discovery at the University of Louisville may help scientists test the effects of exposure to green plants “greenness” on health. Pawel Lorkiewicz, associate professor of chemistry and environmental medicine at , measured a person’s exposure to trees and plants by testing their urine.

Limonene is a nontoxic substance emitted into the air by many trees and plants. Concentrated limonene has a lemony smell and is used in perfumes, foods, cleaning and other household products. When a person breathes concentrated limonene, the body breaks it down into metabolites which can be measured in their urine.

These metabolites also are in a person’s urine after they spend time in a forest, . This means the metabolites can be used to measure a person’s exposure to trees and plants. Comparing this exposure with health information may help researchers more accurately determine whether time spent in nature is beneficial for an individual’s health.

“Even though we may not smell limonene exactly, usually we can tell that we are surrounded by trees and greenness because of the smell. Parks and forests, or even meadows or larger green spaces have a characteristic smell because of plant volatile organic compounds such as limonene,” Lorkiewicz said.

For several years, Envirome Institute researchers have been studying the health effects of living near trees and greenness. As part of the , they planted trees and shrubs in specific neighborhoods, measuring changes in the residents’ health compared with those living in areas with fewer trees. But the researchers found it challenging to accurately measure an individual’s actual exposure to trees. There may be many trees where they live, but they spend much of their time working in tree-sparse locations or indoors, insulated from trees and plants.

So the team searched for a way to measure how much time an individual spent around greenness. Because many trees and plants release significant amounts of limonene into the air, they developed a method to test for limonene exposure using urine, which is easy to collect.

After testing the urine of people who smelled pure limonene from a vial, they compared those results with urine from people who spent time walking in a forest. They found the same metabolites in the urine of both groups, tagging three of them as reliable biomarkers of exposure to greenness.

“It was very exciting. That’s what constitutes a biomarker, something was released by trees in real life, metabolized by our bodies and found in our urine, not just the result of smelling a pure chemical in a lab,” Lorkiewicz said. “So, we objectively can tell when someone is not working in an office at a desk, but they actually go outside and are surrounded by greenness.”

Keith said the biomarker for greenness exposure is a breakthrough for the Green Heart Project, the Trager MicroForest project in downtown Louisville and other studies.

“We have been working with the overall premise that trees affect health in a positive way. Our mission in the Green Heart Project is to understand in some ways how they do that,” she said. “We have turned to the idea of using the human as the biomonitor of greenness in the human. We hope to use this to see changes in people’s overall exposure to greenness as we plant trees and determine whether those changes correlate to changes in health.”

To assess people’s exposure to trees and plants, Keith combines the limonene biomarker test with satellite images showing tree density where people live and surveys of their time spent outdoors and compares the exposure information with health data such as blood pressure and heart rate.

In additional research, Keith and her team are using the biomarker to compare the health effects of limonene and other compounds emitted by plants on the body.

The Nature Conservancy is overseeing the planting of approximately 8,000 trees and shrubs in the designated neighborhoods. Researchers with the University of Louisville’s Christina Lee Brown Envirome Institute will compare data about the health of people living in the neighborhoods and air pollution levels collected before the plantings with data collected two years after the vegetation is planted. The results will provide insight into how the additional vegetation affects the health of people in the community.

“Our primary objective is to understand how increasing greenness affects the risk of heart disease within the community,” said Aruni Bhatnagar, PhD, director of the at the University of Louisville, who oversees the project. “Heart disease remains the leading cause of death throughout the world. We can treat heart disease with stents and statins, but we cannot prevent the disease. If we can show that putting in more trees will lower the incidence of the disease, even by a fraction of what it is, that would be a major achievement.”

The Nature Conservancy is planting the trees and shrubs in designated residents’ yards at no charge to property owners.

“We’re excited to enter the next phase of the Green Heart project,” said David Phemister, state director for in Kentucky. “Tree plantings at this scale require strong partnerships and deep engagement with the community. Green Heart is not just a science experiment – it is a deep investment to bring more nature to neighborhoods in the heart of Louisville.”

The residents’ health is being assessed by UofL researchers through the Health, Environment and Action in Louisville (HEAL) Study. The HEAL researchers obtained health information from approximately 700 participating residents of the Taylor-Berry, Jacobs, Hazelwood, Oakdale, Wilder Park and Beechmont neighborhoods before the planting began. They collected information such as blood pressure, cholesterol, heart health and other health indicators. The same participants will be evaluated again in two years to determine if these health indicators have changed.

“We wanted Louisville to become maybe one of the first cities in the country that makes its decisions through the lens of all forms of health,” said Christina Lee Brown, benefactor of the Envirome Institute. “That is the Envirome’s objective. This project is a magnificent example of healing our community from the roots up.”

In addition to the Envirome Institute and The Nature Conservancy, the project is funded by the National Institutes of Health and is supported by partnerships with Metro Louisville, Louisville Grows, Washington University in St. Louis, Hyphae Design Laboratory and the United States Forest Service. The total cost of the five-year project is more than $15 million.

A UofL video about this project is available on .

Aruni Bhatnagar, PhD, director of the at UofL, will discuss the research, the , at the next Beer with a Scientist event on March 14.

“No one knows whether and to what extent trees and neighborhood greenery affect human health and why,” Bhatnagar said. “This work will tell us how to design a neighborhood that supports human health and whether an increase in the urban greenspaces and vegetation could enhance physical and mental health by decreasing the levels of ambient air pollution.”

The Green Heart Project is a collaboration of UofL, The Nature Conservancy, Hyphae Design Laboratory, the Institute for Healthy Air Water and Soil, the U.S. Forest Service and the City of Louisville. The goal of the project is to assess how residential greenness and neighborhood greenspaces affect the health of our communities by decreasing the levels of pollution and promoting physical activity and social cohesion.

The talk begins at 8 p.m. on Wednesday, March 14, at Against the Grain Brewery, 401 E. Main St. in Louisville. A 30-minute presentation will be followed by an informal Q&A session.

Admission is free. Purchase of beer, other beverages or menu items is not required but is encouraged.

At the next Beer with a Scientist, April 18, Deborah Yoder-Himes, PhD, will discuss super bacteria, antibiotic resistance and why everything is labeled “anti-bacterial.”