A childhood spent close to green space is an important factor in mental health later in life, according to a new study by researchers from the Department of Bioscience at Aarhus University in Denmark.
Their paper, recently published in the Proceedings of the National Academy of Sciences of the United States (PNAS), found that the children in their study who grew up with the lowest level of nearby green space “had up to a 55 percent higher risk of developing a psychiatric disorder independent from effects of other known risk factors.”
Led by Kristine Engemann, a post-doctorate at the Department’s section for Biochange, researchers used high-resolution satellite data to calculate the Normalized Difference Vegetation Index (NDVI) within 210-by-210 square meters around more than 950,000 homes. They then correlated that information with records from the Danish Civil Registration System on the mental health and socioeconomic status of almost 1 million people. The researchers looked at people born between 1985 and 2003, concentrating on where they lived between birth and the age of 10.
“Residences were chosen based on everyone in Denmark that we could get information from,” Engemann explains. “We had access to data from the Landsat satellite going back to 1985. Then we were limited to people who were still living in Denmark after the age of 10, and also people who had been living in Denmark during the entire time from birth to age 10.”
While green space can be anything from a park to a piece of urban woodland, a backyard or a communal garden in an apartment complex, the study found that benefits for children are dosage-dependent. In other words, both the amount of green space and the amount of time the child lived near it factored into his or her risk of developing any one of 16 psychiatric disorders.
“We looked at the smallest square [210-by-210 square meters] and then up to almost a [square] kilometer,” says Engemann, “and we found the strongest association with the vegetation was that closest to peoples’ residences.”
What’s more, even children from families with few resources will be healthier for the presence of green space in their lives. “Even after adjusting for socioeconomic status, we still see an association with green space,” says Engemann.
What exactly we get from growing up near trees, greenery and other features of a natural environment is still a question, though. According to the paper, “A number of psychological and physiological mechanisms might link elements of green space to decreased risk of psychiatric disorders.”
Growing up in an urban environment has been linked to high neural activity caused by stress processing, which could lead to a higher risk of psychiatric disorder in adults. But green space, the paper states, “can enhance psychological restoration” and “mitigate negative effects from the socially dense and noisy city environment that heighten stress.”
“What we are really excited about with the study,” says Engemann, “was that we saw such broad effects, that we are seeing this association with green space across so many different psychiatric disorders, and that it was clear across the entire Danish population. That tells me that this is something we can really use to improve the environments of our cities.”
Mental disorder is on the rise globally, according to the World Health Organization. “It has been predicted that more and more people will suffer from some form of mental illness,” she says, “and at the same time more and more people are moving to cities.” With city planners and politicians often targeting green areas within cities for housing and commercial development, Engemann hopes that the evidence presented in the study can help provide opponents of such projects with robust counterarguments. “It’s not just a question of aesthetics,” she says. “Conserving or adding more green space in your cities can actually lead to a big health benefit long-term and create much healthier cities.”