Your job as an urban forester saves lives. Every tree planted, every city greened, every forest managed, and green space created has an indelible impact on the human lives nearby. The evidence for trees’ beneficial impact on human health is mounting, replacing the belief that trees are simply aesthetically pleasing or clean air and water machines. In myriad ways, we are seeing research support what we have felt in our hearts to be true: Trees really are the answer.
Let’s take heart disease, the number one killer in the U.S. today. One in four Americans deaths is caused by heart disease each year, at a cost of $219 billion and climbing. Most people are familiar with risk factors such as smoking, unhealthy diet, excessive alcohol use, and inactivity, but a study by U.S. Forest Service researcher Geoffrey Donovan, Ph.D. et al. showed that a decrease in access to forested green space is another likely risk factor. The researchers looked at data on cardiovascular deaths in 15 states prior to the deforestation attributable to emerald ash borer, and again after the loss of 100 million ash trees. They found the loss of ash trees was responsible for an additional 15,080 heart disease deaths, even when controlling for other factors that could contribute. Other studies, from Toronto to Miami, have shown similar relationships—people living in greener areas have lower rates of heart disease.
In 2017, Dr. M. van den Bosch et al. rigorously analyzed a combination of 13 meta-analyses reviewing the existing literature on green space exposure and health. They found that areas with increased green space around the locations where people lived led to a significant reduction in cardiovascular disease. The proximity to green space seemed to have several positive effects on heart disease risk factors and also showed a protective effect on heart disease independent of the other benefits.
How can trees reduce heart disease deaths?
Just as several elements affect the formation of heart disease in the first place, trees seem to have a multifactorial benefit. Multiple studies have found that trees reduce air particulates and urban heat, and even lower incidences of obesity. Tree proximity increases physical activity and lowers blood pressure and stress levels—even balancing blood sugar levels in diabetics—which translates to lower overall cardiovascular disease risk. Some scientists propose that certain chemical compounds released from trees may act on our immune and endocrine systems directly, reducing the release of stress hormones and inflammation, but more studies are needed to solidify this link.
The body of research in this field is still new but growing. A search on the medical journal database PubMed of “cardiovascular disease benefits green space” returned 166 articles, but many more studies are being published in journals outside of medicine. A Google Scholar search with the same criteria revealed 3,180 published articles from 2020 alone, indicating the breadth of worldwide interest in the topic. The research is becoming more refined and higher quality as well. A study called the Green Heart Project, out of Louisville, Kentucky, is the first randomized, controlled trial to look prospectively at the impact of trees on cardiovascular disease. This is the gold standard of study design, and their pilot study data suggests that it will show similar disease-reducing outcomes. With studies such as these, we may have the scientific weight to shift policy and urban design in areas that amplify trees’ benefits not only for stormwater or beautification purposes but to also exert a healing effect on communities. The research shows we need the healing embrace of trees around our homes, workplaces, schools, and play spaces. So go hug a tree back—it’s good for your heart.
Dr. Jennifer Wisdom is a Family Medicine physician with a passion for trees and human health.