Newborns Who Live Near Trees Tend to be Healthier: New Data Suggests That This is Not Because Healthier People Live Near Parks

The link between proximity to green spaces—including trees and parks—and healthy births is widely recognized. Now, new data from researchers at Drexel University’s Dornsife School of Public Health provides further insights into these health benefits. The study takes into account other factors that may influence this link, such as education, income, and body mass index. It also expands our understanding of this link by examining the effects of living near newly planted trees. The results were recently published in the journal Science of The Total Environment.

How Planted Trees and Birth Weight are Related

Using a unique data set—the planting of more than 36,000 trees between 1990 and 2020 in Portland, Oregon, by the non-profit organization Friends of Trees – the researchers measured the number of newly planted trees within 100 meters of the mother’s address in the first 10 years after the birth of her child (using birth data from January 1, 2015, to December 31, 2020, from the Oregon Health Authority) the number of newly planted trees within 100 meters of the mother’s address, the existing tree cover, and the road cover in that area.

Taking into account factors that can influence birth weight, such as the mother’s ethnicity, whether it was her first birth, her BMI, and her level of education, the researchers found a link between the number of trees planted and higher birth weight. In addition, planting trees nearby, including new and existing trees, was associated with three important indicators of newborn health: higher birth weight, lower risk of low birth weight for gestational age, and lower risk of premature birth. For example, each tree planted within 100 meters of the mother’s home within 10 years prior to the birth of the child was associated with a statistically significant increase in birth weight of 2.3 grams. Unlike previous studies that also examined green spaces and pregnancies, the current study took existing tree cover into account to focus on the role that newly planted trees can play in newborn health.

“Although mature trees offer benefits, we find that newly planted trees are also associated with healthy birth weight,” said lead author Yvonne Michael, ScD, professor and interim chair of the Dornsife School of Public Health. ”This is further evidence that planting trees is a relatively simple and inexpensive way to improve public health from early childhood onward.” Living within 100 meters of at least 10 trees was associated with a birth weight that was about 50 grams higher, according to the researchers. The positive impact of trees on birth weight typically peaks at about 10 trees, the researchers found. Stress is associated with an increased likelihood of preterm birth and poorer health outcomes later in life. The authors suggest that older, established trees near the home may have greater benefits than newly planted ones, as they also contribute to mental recovery. Other studies have shown that a developed natural environment exerts a “gentle fascination” – in contrast to the psychologically stressful properties of buildings and other aspects of the built environment.

Effects of Green Spaces on Health

“It’s rare to get detailed information about large-scale tree planting for research purposes,” Michael said. ”Existing tree cover is often closely linked to factors such as income, education, and ethnicity, which makes it difficult to fully account for other possible explanations when studying birth outcomes. By focusing on newly planted trees, we were able to reduce the bias—essentially treating it like a natural experiment. We also observed improvements in birth outcomes after the trees were planted, establishing a temporal link.”

In the current study, existing trees, but not newly planted ones, helped mitigate some of the negative effects of road density—the ratio of the length of roads in an area to its total area—on birth weight. The authors speculated that this might be due to the more developed leaves of established trees, which are better equipped to protect against road noise and air pollution.

Although the authors observed a decline in birth weight in babies during the study, they attributed this to other factors associated with lower birth weight, such as rising air temperatures and dangerous smoke from forest fires (in 2020) in the region. The authors’ data showed that ethnicity, education level, and even existing tree cover were not associated with newly planted trees in an area. The authors point out that a randomized controlled trial is needed to conclusively prove that trees cause these positive health effects. However, the current study provides some of the best available data supporting the link between trees and positive birth outcomes. The current study follows several works examining the effects of green spaces on health, including a 2013 study published by Michael and colleagues, which found that the loss of 100 million trees due to an invasive pest, the emerald ash borer, coincided with an increase in deaths from heart disease and lower respiratory disease in counties with higher tree loss due to the pest infestation.