Growing up in the city can be great for kids. Urban environments offer easy access to essential services like sanitation, health care, nutrition and education, not to mention all the fun activities that cities have to offer. But there are downsides to urban living, including limited amounts of green space—something that may have a lasting impact as children move into adulthood.
According to Jonathan Lambert of NPR, an expansive new study suggests there is an association between a lack of exposure to greenery in childhood and risk of mental illness in later life. The research, published in PNAS, encompassed nearly one million subjects in Denmark who were born between 1985 and 2003. The data was drawn from the Danish Civil Registration System, which records information like gender, place of birth and, crucially, a PIN number that is updated with each change of residence. PINs also link registrants to national databases tracking their socioeconomic and health status, among other things. The researchers, in other words, had access to a breadth of information about their subjects, allowing them to control for a variety of factors that might affect mental health.
Using satellite data, the researchers were then able to map the greenery around the homes where subjects lived from birth to age 10. They found that growing up with limited access to green space was associated with a 15 to 55 percent higher risk of developing one of 16 mental health conditions in adulthood. “The association remained even after adjusting for urbanization, socioeconomic factors, parental history of mental illness and parental age,” the study authors write.
It’s important to remember here that correlation doesn’t imply causation; the researchers cannot and are not saying that being raised around green spaces leads to better mental health, only that there is an association between greenery and mental well-being. But other studies have yielded similar findings. A 2009 study of people in the Netherlands, for instance, showed a relation between living environments with plenty of green space and a reduced risk of anxiety disorder and depression. In 2015, researchers found that children in Barcelona who attended schools surrounded by greenery displayed higher cognitive development than those who attended schools with little green space. A recent outline of existing research on this subject concluded that “[i]ndividuals have less mental distress, less anxiety and depression, greater wellbeing and healthier cortisol profiles when living in urban areas with more green space compared with less green space.”
If green spaces do contribute to better mental health, it isn’t clear why. But the study authors outline a number of possibilities. Greenery enhances “psychological restoration,” they write, which may “mitigate negative effects from the socially dense and noisy city environment that heighten stress.”
“For children, if you come back from school and you have a nice yard or you go to the park, that could help children restore their mental capacity faster,” lead study author Kristine Engemann tells Quartz’s Jenny Anderson.
Vegetation and trees also filter air pollution, and previous research has found tentative links between pollution and psychiatric disorders, though further investigation is needed. There is also some evidence that nature can improve immune functioning, “which has been linked to mental health,” the study authors write.
Though much about the connection between greenery and mental health is not understood, the researchers believe that natural spaces should feature prominently in city designs—something that is not always the case, especially across different socioeconomic neighborhoods. "Ensuring access to green space,” they write, “and enhancing opportunities for a diverse range of uses, especially in densifying urban environments, could be an important tool for managing and minimizing the global burden of disease increasingly dominated by psychiatric disorders.”