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.

In the first study, UofL researchers Aruni Bhatnagar, professor of medicine and director of the Envirome Institute, Ray Yeager and Daniel Riggs, with Carver Coleman and Arden Pope of Brigham Young University and others, analyzed retrospective data from more than 5.5 million cancer patients and survivors from 2003 to 2016. They found that cancer patients in greener counties lived longer than those in counties with less greenness. The protective effects of greenness against cancer mortality were seen with both males and females and individuals of all ages, but were more pronounced at urban locations. Individuals with cancers that were highly survivable – such as breast, prostate and skin cancer – benefitted more from greenness than those with cancers with low survival rates such as brain, esophageal, liver, lung and pancreatic cancer.   

The study, “,” published in the journal Environment International, evaluated associations between greenness and fine particulate matter in the air on causes of death in a large group of cancer patients and survivors in the United States.

“This is the largest study of the relationship between greenness and cancer mortality, and it provides clear evidence that living in green areas is beneficial to cancer patients,” said Bhatnagar “However, we do not yet understand why greenness protects against cancer mortality. Much more remains to be done to see whether greenness benefits cancer patients by lowering mental stress and anxiety or by reducing the levels of air pollutants or whether some other mechanisms are at play.”

The study also found that cardiopulmonary disease, but not cancer, was associated with higher levels of fine particulate air pollution. Mortality from cardiopulmonary causes – stroke, heart attack or COPD – was not affected by county greenness, except in rural locations.  

Greenness and depression

A second study, led by Kandi Walker and Joy Hart, professors in the UofL Department of Communication, Bhatnagar and other researchers in the Envirome Institute, found that people’s satisfaction with levels of greenness in their neighborhood was associated with lower levels of self-reported depressive symptoms.  

The researchers surveyed participants about their perceptions of greenness in their neighborhoods and their mental health symptoms and found that those who were more satisfied with the greenness surrounding their homes also reported lower depression symptoms on a health survey, the Patient Health Questionnaire-9.

The 44.5% of survey participants who reported they were satisfied with the level of greenness in their neighborhood collectively scored better on the health questionnaire for depression.

“Given the pervasiveness of depression in the U.S. population, any changes that can reduce depression are essential, particularly those that can affect a large number of people,” Hart said. “The findings of this study suggest that greening interventions that focus on greenness satisfaction may be a strategy to reduce depression in urban populations.”

The study, “,” was published in July in the journal Population Medicine.

South Louisville study participants needed

Participants in the greening satisfaction study were part of the Health, Environment and Action in Louisville (HEAL) study of the Great Heart Project, which is an ongoing assessment of the effects of neighborhood greenness on individual health. Additional participants are needed for the HEAL Study by the end of September. More information is available on the website.

“Together, these studies add weight to the importance of trees, shrubs and other vegetation in urban areas in benefitting and nurturing human health. Accumulation of such evidence strengthens the case that increasing greenness in urban locations can decrease the high rates of non-communicable diseases in cities,” Bhatnagar said. “And since greenness improves health in general, it may also be effective against infectious disease.”

The research, led by Aruni Bhatnagar, professor of medicine and director of the UofL Christina Lee Brown Envirome Institute, was published ahead of print in the .

Previous studies have shown that proximity to green space — trees and other vegetation — can lower blood pressure levels and the risk of heart disease. A number of environmental factors may come into play, including increased opportunity for outdoor exercise, reduced mental stress and socioeconomic status. However, the relationship between vascular (blood vessel) health, green space and air pollution has not been fully explored.

In this , researchers looked at the arterial stiffness of adult volunteers with co-occurring conditions such as obesity, high blood pressure, diabetes and high cholesterol, that put the volunteers in the moderate-to-severe risk category for heart disease.

“Although we have known for a long time that exposure to air pollution has adverse effects on our blood vessels, this study shows that those who live in greener neighborhoods may be less affected,” Bhatnagar said. “Therefore, one way of preventing the harmful health effects of air pollution may be to make neighborhoods more green.”

Using study participants’ residential addresses and data from the U.S. Geological Survey and local Environmental Protection Agency monitoring stations, the research team analyzed environmental factors where the volunteers lived, including:

• Vegetation index, including the amount of and variation in greenness levels within 200-meter and one-kilometer (0.62 miles) radii around each volunteer’s home.
• Particulate matter, tiny toxic particles invisible to the naked eye, in the air.
• Levels of ozone, a colorless, toxic gas and significant air pollutant.

At times when the particulate matter and ozone levels were high, participants had higher levels of arterial stiffness, however, those who lived in areas with more flora had better blood vessel function. Trees and other greenery offset vascular dysfunction that air pollution causes, the researchers explained.

In previous work, the researchers found that individuals who live in areas with a large amount of greenness show lower exposure to volatile chemicals and have greater household income. In the current study, they explored the relationships between greenery, air pollution and arterial stiffness and found a similar correlation between the U.S. Geological Survey’s normalized difference vegetation index and average household income. Even when adjusting for self-reported lifestyle habits such as exercise and smoking — 70% of the volunteers were nonsmokers — the researchers found that “the effects of green spaces on hemodynamic function are largely independent of median household income, physical activity levels and tobacco use.”

“These findings indicate that living in green areas may be conducive for vascular health and that the [favorable] effects of greenness may be attributable, in part, to attenuated exposure to air pollutants such as [particulate matter] and ozone,” said Daniel Riggs, UofL biostatistician and the study’s first author.

This research was conducted in conjunction with the Green Heart Project, a first-of-its-kind study of the effects of plants on human health, led by researchers at the .

From December 10-14, project researchers tested 700 individuals in South Louisville for both active infection and antibodies, indicating previous infection, to develop a “snapshot” of the rates of infection in that area of the county. From those test results, the researchers estimate that as of these dates, nearly 11.16% of South Louisville residents have been exposed to the virus. Extending this estimate to all of Jefferson County would mean that nearly 73,636 individuals (1 in 10) have been infected with SARS-CoV-2 since the beginning of the pandemic. 

“The latest rates are the highest we have seen since we began testing in June and are higher than we had expected based on our previous testing drives,” said Aruni Bhatnagar, director of the UofL Christina Lee Brown Envirome Institute. “These rates show that the pandemic continues to grow at an accelerated rate. Indeed, it is likely to get worse before getting better.”

Key findings from the project’s latest round of testing:

• About 3.57% of those tested had an active coronavirus infection.
• Antibody testing indicates that the true rates of infection may be 1.6 times higher than reported in publicly available data.
• More than 28,000 Louisville residents may have been infected between November and December.
• About 73,000 people in Louisville likely have had a coronavirus infection at some point since the beginning of the pandemic, based on antibody testing.
• The highest rates of infection in December were found in people 18-to-34 years of age (10%), which was four times higher than those 35-to-59 years of age (2.6%).
• Women and men had similar rates of infection.
• Current rates of infection were much higher among non-whites (8.8%) than among whites (1.43%). To-date, nearly twice as many non-whites as whites have been infected by the virus.

The is a unique series of studies to estimate the true prevalence of SARS-CoV-2, the virus causing COVID-19, in Jefferson County. This phase of the project involves testing a representative sample of individuals from different areas in the city in proportion to the age and race of the population of the area. For this round of testing, the project researchers tested individuals living in South Louisville neighborhoods that are part of Green Heart Louisville, a separate, ongoing project to test whether increasing green space in a neighborhood improves air quality and human health.

Data released for the December tests show at least 3.57% of participants from the area were currently infected by the virus, which is nearly double the rate reported for the entire County in November (2%).

The project researchers with the , directed by Kenneth Palmer, also tested samples from the participants for antibodies against the virus and found a 1.6-fold increase in the number of individuals who previously had been exposed to the virus. Study researchers estimate that by December 14, about 73,000 individuals had been infected by the virus rather than the 48,228 known cases documented so far. These data also suggest that approximately 15,000 individuals became infected between November and December.

“Reasons for the increase in the rates of infection are not clear, but may relate to a drop in temperature,” Bhatnagar said. “From our previous work we know that . However, part of the reason may also be fewer precautions by young people and increased travel during the Thanksgiving holiday.”

Bhatnagar said he expects infection levels to continue to rise due to colder weather temperatures.

“Our models suggest that infection rates likely will continue increasing at least until the end of December and that things are likely to get much worse in the coming months as temperatures dip even further,” he said. “We are entering the most dangerous and deadly phase of the pandemic and we have to maintain high vigilance for at least the next two months until the temperatures begin to rise again or a large number of individuals are vaccinated.”

“In what may be a glimmer of hope, we have seen a consistently increasing awareness of the importance of repeated COVID-19 testing among the residents of Jefferson County, especially the South Louisville area where there was a robust push for testing and awareness by the local community members,” said Alok Amraotkar, a postdoctoral research fellow in the Envirome Institute who conducted the study. “We will keep building on these relationships with the community to curb the spread of COVID-19 virus.”

In an effort to obtain a uniform sample of residents, investigators at the Brown Envirome Institute mailed 20,000 letters to households across the study area. The invitations were sent to individuals selected using addresses derived from U.S. Census Bureau tract boundaries. In addition, any adult resident of the area was invited to participate through news, emails and social media messages.

Nearly 1,000 individuals were tested, 700 of whom live in the Green Heart Louisville study area. The testing took place at community drive-up or walk up locations. Participants were tested both for the presence of the virus via nasal swabs, indicating current infection, and for antibodies against the virus in their blood, indicating a previous infection. Samples for the virus were tested by Bluewater Diagnostic Laboratory and antibodies were measured at UofL’s Regional Biocontainment Laboratory by the .

Wastewater monitoring results reinforce findings

The Co-Immunity Project also has been monitoring the presence of SARS-CoV-2 in Louisville wastewater in collaboration with MSD since June. During this round of community testing, daily wastewater samples were gathered from seven manhole locations within the study area. All locations revealed daily presence of the virus at levels consistent with those found across Louisville in this time period. These levels are 10 times higher than area levels just six weeks ago.

The researchers are planning to conduct a fourth round of randomized coronavirus testing in Jefferson County January 22-28.

This study was supported in part by the City of Louisville, the James Graham Brown Foundation, the Owsley Brown Family Foundation, Foundation for a Healthy Kentucky, the Jewish Heritage Fund for Excellence and others.