The mental health benefits of living closer to nature

Although more than half of the world’s population live in cities, urban living has been linked to various adverse health outcomes. Studies have shown that the rates of mental illnesses like anxiety, post-traumatic stress disorder, and depression are generally higher in cities as compared to rural areas. In addition, individuals who spent more years in an urban environment as a child had a greater risk of developing schizophrenia as an adult.

Kristine Engemann, a postdoctoral researcher in the Department of Bioscience at Denmark’s Aarhus University, wanted to explore whether the opposite was true as well. As a lifelong nature lover, she wondered if being surrounded by more nature during childhood could lower a person’s risk of mental illness in the future. Such findings could emphasize the health benefits of integrating more residential green space into urban planning.

“Finding an association between green space and mental health could potentially be used to guide the design of healthy city environments, as well as institutions and programs affecting childhood life — for example, school systems,” said Engemann.

Along with her colleagues, Engemann used data extracted from multiple Danish population-based registers with high-resolution satellite images. They combined longitudinal data on mental health outcomes with the amount of green space located around each individual’s residence. Their findings indicate that children who grew up with the lowest levels of green space had up to 55 percent higher risk of developing a psychiatric disorder, independent from effects of other known risk factors. The study was published by the Proceedings of the National Academies of Sciences in January 2019.

Participants included everyone born in Denmark from 1985 to 2003, and who were still residing in the country on their 10th birthday (943,027 individuals). Individuals were classified with a psychiatric disorder if they had been admitted to a psychiatric facility, received outpatient care, or visited a psychiatric emergency care unit with a diagnosis of one of 18 psychiatric disorders. Green space presence was calculated as a ratio of green space to total area around a person’s residence using satellite images covering the entire country.

The researchers found that high levels of childhood green space are associated with a lower risk of developing almost all of the 18 psychiatric disorders looked at later in life. When compared to living at the highest levels of green space, the lowest levels of green space were linked to a 15 to 55 percent higher risk for schizophrenia, mood disorders, bipolar disorder, depression, and other conditions. Only intellectual disability and schizoaffective disorder did not show a significant correlation.

The relationship remained even after adjusting for other known risk factors including socioeconomic factors, family history of mental illness, and parental age. In addition, the authors found that the association was stronger when they calculated a cumulative measure of green space from birth to age 10, as opposed to measuring green space at one single year. This suggests that the positive association may build up over time, and thus a continuous exposure to nature throughout childhood could be crucial.

“Finding ways to provide high green space exposure during childhood should be encouraged by parents as well as in sustainable urban planning.”

“Our results could be important for early intervention, but they also complement a number of other studies showing positive associations between nature and mental health,” Engemann said. “Hence, finding ways to provide high green space exposure during childhood should be encouraged by parents as well as in sustainable urban planning.”

“Parents may take action by influencing children’s visits to parks and other green spaces, even if choosing a residence with high amounts of green space in the surroundings is not possible. For city planners, our results suggest that maintaining or even increasing green space in residential areas could potentially lead to significant health benefits.”

The question whether or not exposure to neighborhood green space is actually the cause for improved mental health outcomes cannot be answered with this study design. Also, the question remains why natural environments would have a possible protective effect on mental health.

A possible reason might be that readily available green space may enhance psychological restoration — as in, the recovery from attentional fatigue and stress. City dwellers experience information overload, loud noise, and crowding, and a walk in the park could serve as some relief. More green space in neighborhoods has also been found to decrease air pollution, positively affect social cohesion, and encourage residents to be more physically active.