Could Living Near More Trees Boost Your Heart?

Living in a neighborhood with a high concentration of trees could significantly lower levels of inflammation and, importantly, decrease the risk of heart disease, new research from Green Heart Louisville’s first wave of clinical research from its HEAL study shows.

Aruni Bhatnagar, the medical professor and cardiology researcher at the University of Louisville who is spearheading the project, told The Washington Post that he wanted to “do something” about the air pollution plaguing the city. His solution was to plant thousands of trees in Louisville neighborhoods and methodically study health data from participating residents to see the effect they had on health. 

“We are trying to see if we can decrease the rates of heart disease in a community,” Bhatnagar told NBC.

The results showed a “significant decrease” in levels of hs-CRP, an important marker for inflammation, in areas where tree and shrub counts were more than doubled. In excess, inflammation is known to contribute to a laundry list of diseases and illnesses, including cancer, Alzheimer’s disease, diabetes, obesity, and as the study points out, heart disease. 

“I wouldn’t have expected such a strong biomarker response, Peter James, director of the Center for Occupational and Environmental Health at the University of California, Davis School of Medicine, told NBC. “And that speaks to maybe something truly is causal here with how trees impact health.” 

Bhatnagar is leading dozens of researchers who are monitoring the health data from more than 750 participants, who range from 25 to 75 years old. The participants are part of a middle-income neighborhood, which tend to have both fewer trees and worse health outcomes compared to affluent neighborhoods.

^{Map of the Green Heart Louisville Project area showing neighborhoods where trees were planted and those where no trees were planted for the project. University of Louisville}

Some previous research has shown that people living in greener spaces tend to have better health outcomes, but the fact that most of those greener spaces happened to be in wealthy areas raises some questions. Namely, whether living in green areas can truly lead to improved health, or whether there were other factors to consider, like socioeconomic-related differences in levels of elevated stress — which has also been shown to lead to inflammation — or access to healthcare.

“We can’t just go, ‘Oh, look, this is [a] greener place and people are happier’ because most places that are greener are richer, etc.,” Bhatnagar told The Washington Post. He also mentioned his interest in the Bradford Hill criteria of causation, a group of nine scientific principles to determine whether there is a true causal — or cause and effect — relationship between two correlated things, or if the correlation is merely coincidental.

“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,” Bhatnagar told Medical Xpress. “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.”