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.

Periods of extreme heat often result in an increase in deaths, mostly related to heart conditions. A UofL research study shows that heat also can impair the immune system and increase damaging inflammation, according to Daniel Riggs, assistant professor of environmental medicine and affiliated with .

Riggs and his colleagues recorded levels of immune cells and biomarkers in the blood of 624 participants in Louisville during summer months. They then compared those levels with the Universal Thermal Climate Index for that day, which factors in air temperature, relative humidity, wind speed and ultraviolet radiation levels as a measure of heat exposure.

They found that when it was hotter, the participants had higher levels of immune molecules in their blood, indicating a general immune response and inflammation, as well as lower levels of B-cells, which allow the body to fight specific infections. This means that with higher heat, people may be more susceptible to infection and more sensitive to environmental exposures, which in turn can contribute to worsened heart disease.

“We know that certain changes in the immune system and increased inflammation are a leading mechanism in many types of cardiovascular disease. Our findings suggest that heat exposure could be contributing to these processes that ultimately lead to greater risk of cardiovascular disease,” Riggs said.

Riggs presented at the American Heart Association Epidemiology, Prevention, Lifestyle and Cardiometabolic Health Conference in March.

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.”