Living in a neighborhood full of trees may be as beneficial to your heart as getting regular exercise, a new study suggests.
Researchers at the University of Louisville designed a clinical trial that followed hundreds of people living in six low- to moderate-income neighborhoods in South Louisville, Kentucky. The team used blood and other samples to better understand how their heart risks changed before and after planting thousands of mature trees near their homes.
Results from the Green Heart Louisville Project’s HEAL Study, released Tuesday, showed that people living in neighborhoods with twice as many trees and shrubs had lower levels of a blood marker associated with heart disease, diabetes and some types of cancer compared to those living in barren neighborhoods.
“We’re trying to see if we can lower rates of heart disease in a population,” said Aruni Bhatnagar, a professor of medicine at the University of Louisville who led the project.
Most previous research showing the effects of nature on mental and physical health is observational and cannot answer the question of whether people living in greener communities are healthier because they are wealthier and have access to better healthcare.
The HEAL study was set up with a control group and an intervention, meaning that some of the participants were exposed to something measurable during the study but not beforehand.
Bhatnagar and his team recruited about 750 people living in a 4-mile stretch of south Louisville crisscrossed by a highway, with residents ranging in age from 25 to 75.
About 80% were white and 60% identified as female. Half reported a median household income of $50,000.
The researchers collected blood, urine, nail and hair samples, as well as health data from each person before starting the intervention.
Then, from 2019 to 2022, they planted about 8,500 evergreen trees, 630 deciduous trees (types that shed their leaves in the fall), and 45 different types of shrubs in parts of the 4-mile study area, while leaving others as is.
Last year and this year, new samples were taken from citizens living in both regions.
People living in intervention areas had 13% lower levels of high-sensitivity C-reactive protein, a blood marker associated with heart disease, including stroke, coronary artery disease and heart attack. The decrease was similar to starting a regular exercise routine, Bhatnagar said.
“I didn’t expect such a strong biomarker response, and it suggests there really is something causal in the effect of trees on health,” said Peter James, director of the Center for Occupational and Environmental Health at the University of California, Davis School of Medicine, who was not involved in the new research.
How can trees improve physical health?
Previous studies have shown that spending time in green spaces improves mental health.
Living among more trees is linked to improved physical health, new research has found.
Trees shade and cool areas where they are planted, helping to reduce the effects of urban heat, which disproportionately affects low-income neighborhoods and neighborhoods of color. Hot weather worsens heart disease and can cause heat stroke in people without preexisting conditions.
Trees also block out noise, which has been linked to higher rates of cardiovascular disease, James said.
“They provide spaces where people can relax, exercise, and probably more importantly, socialize,” Joan Casey, an environmental epidemiologist and associate professor of environmental and occupational health sciences at the University of Washington, said in an email.
“They also displace other harmful land uses, such as industrial areas,” he said.
Bhatnagar and his team believe that because one of the city’s main highways runs through the study area, the trees’ ability to filter air pollution and prevent neighborhoods from constantly breathing in harmful particles may be the primary way the tree-planting intervention lowers inflammatory markers in people living in green spaces.
During the study, the project planted trees only in the areas of South Louisville with the worst air quality. It took air quality samples before the project and is still analyzing how the new tree cover affects pollution. It’s a complex endeavor because air quality fluctuates with the weather — a windy day can increase or decrease air pollution in certain areas, depending on the wind direction, and air pollution is worse on hotter days.
The project plans to plant trees in control neighborhoods in three or four years, if the intervention neighborhoods continue to show positive results. It also wants to determine whether tree cover improves sleep or children’s immune systems by encouraging outdoor play.
“There’s no conclusive evidence,” Bhatnagar said. “But this is the strongest evidence of any study yet on trees and their relationship to health.”
Growing evidence shows the importance of distributing green space evenly across cities, but this is not currently the case.
Casey said urban planners need to be careful not to create “green gentrification” when cities provide more equal access to green space, meaning areas like waterfronts are restored and housing prices increase as a result, making it unaffordable for existing residents to continue living there once the green space is completed.
“The lesson here is that nature is not an amenity; green spaces are not a privilege for the rich. They are essential to us as humans,” James said.
This article was originally published on NBCNews.com