A Walk in the Park: Green Space in Childhood Good for Mental Health

Image above: Bryant Park in New York City. Source: Wikipedia.
Photo by Jean-Christophe Benoist, https://commons.wikimedia.org/w/index.php?curid=19274240.

Article: Engemann, K., Pedersen, C. B., Arge, L., Tsirogiannis, C., Mortensen, P. B., & Svenning, J. C. (2019). Residential green space in childhood is associated with lower risk of psychiatric disorders from adolescence into adulthood. Proceedings of the National Academy of Sciences, 116(11), 5188-5193. https://www.pnas.org/content/116/11/5188.

Picture a house. Does it have a yard? Plenty of trees? Lots of grass? Room to roam? This image can be accurate in rural areas, small towns, and suburbs. Urban areas (cities) are different. Cities are crowded, and not just with people. There is a lot of everything: roads, buildings, cars, buses. All these people and things have to share the available land. Open land, like green spaces, is sometimes squeezed tighter or eliminated entirely. As a recent paper shows, this lack of green space can lead to lifelong negative consequences for mental health.

The research team, from Aarhus University, conducted their study among people born from 1985 to 2003 in Denmark. The residents of Denmark each have a unique personal identification number (PIN). This PIN is used for any kind of official process or information. Each resident’s PIN is linked to his or her place of birth, incomes, address, and clinic/hospital visits – in the same way that social security numbers in the United States are linked to this information for Americans.

Skyline of Copenhagen, the capital of Denmark. Source: Wikipedia.
Photo by Ibrahim50, https://commons.wikimedia.org/w/index.php?curid=10725845.

With this information, the research team determined the location of each person’s residence when he or she was 10 years old, and whether it was in an urban, suburban, or rural area. They then looked specifically at the amount of green space in a 30 meter x 30 meter (about 98 feet x 98 feet) square centered on that residence. The researchers examined the green space using satellite photos of the residence areas (a technique called remote sensing) taken during the dates that each person in the study lived at that residence.

Satellite image of Copenhagen. Source: Wikipedia.
Photo by NASA – Satellite imagery taken from NASA World Wind software (by screenshot),
Public Domain, https://commons.wikimedia.org/w/index.php?curid=143799.

The researchers then compared the amount of green space near each person’s residence (a measure called NDVI in the study) when he or she was 10 years old to any instance that he or she received inpatient (hospital) or outpatient (doctor’s office) treatment for psychiatric (mental health) disorders during teen age and adulthood.

For this comparison, they used a measure called relative risk. A relative risk of more than 1 means a higher risk of psychiatric disorder, and a relative risk of less than 1 means a lower risk of psychiatric disorder.

The researchers’ findings are shown below in Figure 2 from the paper below. Each of the five graphs represents one type of area, as shown in the top right of the graph. For example, the upper left graph (marked Rural) shows information from ALL rural areas on Denmark (dark green on the map).

Figure 2 from Engemann et al 2019, showing a map of Denmark, color-coded by urbanization level.

The x-axis on each graph (numbers along the bottom) shows the amount of green space (labeled NDVI) during childhood. In every graph, as green space increases, the relative risk (left edge of each graph) decreases. Since this relative risk is that of psychiatric disorders during adolescence and adulthood, we can see that more childhood green space is associated with a lower risk of these disorders.

Also, in the cities (purple areas, the graphs to the right) the risks of this orders is higher than in the more rural areas ( green areas, graphs to the left). The highest relative risk values in the right-hand side graphs. These values are also generally higher than the values on the left-hand side graphs. So, this data also shows that living in more urban areas in childhood is associated with a higher risk of psychiatric disorders later in life.

Why is this important? The percentage of the world’s population that lives in urban areas continues to grow. In 2017, 54% of the world’s population lived in urban areas, compared to less than 34% in 1960 (Source: The World Bank). The population of the world has increased in that time, too. So, an increasing percentage of an increasing global population is living in urban areas. As this paper shows, living in urban areas is associated with a higher risk of psychiatric disorders, especially in areas with less green space. This means that unless city planners and policy makers ensure adequate areas of green space in urban areas, more and more people in the world will be at a higher risk of developing psychiatric disorders later in life.

Dealing with that mental health burden will not be a walk in the park. However, it’s not all gloom and doom. Find and enjoy your local green spaces. The benefits, as this paper shows, will continue long after your walk in the park.

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Munim Deen

Munim is an epidemiology doctoral student. His primary interests are infectious disease outbreaks and their intersection with the environment, public policy, and society at large. A geographic information system (GIS) devotee, he incorporates mapping and spatial analysis into his work whenever possible. A former newspaper columnist, he holds a bachelor's degree in microbiology and a master's degree in epidemiology.

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