In what is considered one of the largest studies of its kind, the researchers used longitudinal data on 3,568 children and adolescents, aged nine to 15, from 31 schools in London. This period is a key moment in the development of thinking, reasoning and understanding of the world of adolescents.

The study, published in Nature Sustainability, examined the links between different types of natural urban environments and the cognitive development, mental health and general well-being of students.

The environments were divided into what urban planners call green spaces (woods, meadows and parks) and blue spaces (rivers, lakes and sea), with green spaces separated into meadows and woods. The researchers used satellite data to help calculate the daily rate of exposure of each adolescent to each of these environments within 50m, 100m, 250m and 500m of their home and school.

After adjusting for other variables, the results showed that a higher daily exposure to the forest (but not the grasslands) was associated with higher scores for cognitive development and a 16% lower risk of emotional problems. and behavioral two years later.

A similar but weaker effect was observed for green spaces, with higher scores for cognitive development, but this was not observed for blue spaces. The researchers note, however, that access to blue space in the cohort studied was generally low.

Examples of other explanatory variables taken into account included the youth’s age, ethnicity, gender, parents’ occupation, and type of school, for example, state or independent. The level of air pollution may have influenced the cognitive development of adolescents, but the researchers did not consider these observations to be reliable or conclusive, and they require further investigation.

It is already estimated that one in ten children and adolescents in London between the ages of five and 16 suffer from a clinical mental illness and the additional costs are estimated between £ 11,030 and £ 59,130 ​​per year for each person. As with adults, there is also some evidence that natural environments play an important role in the cognitive development and mental health of children and adolescents in adulthood, but less is known why.

The results of this study suggest that planning decisions aimed at optimizing ecosystem benefits related to cognitive development and mental health should carefully consider the type of natural environment included. Natural environments further away from a teenager’s home and school can also play an important role, not just their immediate surroundings.

Lead author, PhD student Mikaël Maes (UCL Geography, UCL Biosciences and Imperial College London School of Public Health) said: “Previous studies have found positive associations between exposure to nature in urban settings, cognitive development and mental health. The reason why these health benefits are received remains unclear, especially among adolescents.

“These findings contribute to our understanding of types of natural environments as an important protective factor for adolescent cognitive development and mental health, and suggest that not all types of environment may contribute equally to these. health benefits.

“Forest bathing, for example (being immersed in the sights, sounds and smells of a forest), is a relaxation therapy that has been associated with physiological benefits, supporting human immune function, reducing the variability of heart rate and salivary cortisol; and various psychological disorders. benefits. However, the reasons why we experience these psychological benefits of the forest remain unknown. “

Joint lead author Professor Mireille Toledano (Director, Mohn Center for Children’s Health and Wellbeing and Investigator, MRC Center for Environment and Health and SCAMP Study Principal Investigator, Imperial College London) said: “It was suggested previously that the benefits of natural environments to mental health are comparable in magnitude to family background, parents’ age and even more important than factors like the degree of urbanization around you, but lower than the socioeconomic status of your parents. Both sensory and non-sensory pathways have been suggested as potentially important in providing cognitive and mental health benefits resulting from exposure to nature.

“It is essential for us to determine why natural environments are so important to our mental health throughout life: do the benefits arise from the physical exercise we do in these environments, from the social interactions we have there? often or the flora and fauna that we enjoy in these environments or a combination of all of these? “

Joint lead author Professor Kate Jones (UCL Center for Biodiversity & Environment Research, UCL Biosciences) said: “One possible explanation for our results may be that audiovisual exposure through vegetation and animal abundance offers psychological benefits, both of which are expected in greatest abundance in the woods. Although our results show that the urban forest is associated with cognitive development and adolescent mental health, the cause of this association remains unknown. Further research is fundamental to our understanding of the links between nature and health. “

To arrive at the results, the researchers analyzed a longitudinal dataset of 3,568 adolescents between 2014 and 2018, whose residence was known, from the Study of Cognition, Adolescents and Mobile Phones (SCAMP) in the London metropolitan area. They assessed the mental health and general well-being of adolescents from a self-reported Strengths and Difficulties Questionnaire (SDQ) – covering areas such as emotional issues, driving, hyperactivity and problems with peers – and the KIDSCREEN-10 questionnaire taken by each adolescent for SCAMP. .

Reference: Maes MJA, Pirani M, Booth ER, et al. Benefit of the forest and other natural environments for cognition and adolescent mental health. Nat Sustain. 2021: 1-8. do I: 10.1038 / s41893-021-00751-1

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