Higher greenness scores are associated with fewer hospitalizations for mental illness

Higher greenness scores are associated with fewer hospitalizations for mental illness

Higher levels of greenness are associated with a lower risk of hospitalizations for mental disorders, says an analysis of data from seven countries over two decades published in theBMJ's climate problem Today.

Local greenery was associated with a 7% reduction in hospitalizations for all-cause mental disorders, with the association being stronger for substance use disorders (9%), psychotic disorders (7%) and dementia (6%). However, the associations varied by country and disease. For example, Brazil, Chile, and Thailand showed consistent protective associations across most disorders, while in Australia and Canada, greenness was associated with slightly increased risks for all-cause mental disorders and for several specific disorders.

The study, led by Professors Shandy Li and Yuming Guo of Monash University in Australia, suggests that this protective effect on a person's mental health increases with increasing exposure to green, without there being a clear threshold.

Professor Guo said the study "provides clear evidence that should be incorporated into urban planning and health policy to better protect mental health," he said.

Mental wellbeing remains a global challenge. It is estimated that 1.1 billion people suffered from mental disorders in 2021, accounting for 14% of the global burden of disease and associated economic and societal costs.

While the links between mental health and green space have been linked previously, the Monash study is the largest, analyzing data from 11.4 million hospital admissions for mental health disorders across 6,842 locations in seven countries (Australia, Brazil, Canada, Chile, New Zealand, South Korea and Thailand) from 2000 to 2019.

In their analysis, the researchers included:

• Alle verursachen psychische Störungen und sechs spezifische Kategorien (psychotische Störungen, Substanzstörungen, Stimmungsstörungen, Verhaltensstörungen, Demenz und Angstzustände).
• Die Grünheit wird anhand des Normalized Difference Vegetation Index (NDVI) gemessen, einer weit verbreiteten und zuverlässigen, von Satelliten abgeleiteten Metrik zur Bewertung des Vegetationsniveaus in einem bestimmten Gebiet.
• Berücksichtigt wurden Faktoren wie Bevölkerungszahl, Wetterbedingungen, Luftschadstoffe, sozioökonomische Indikatoren und Saisonalität.
• Die Modelle wurden nach Geschlecht, Alter, Urbanisierung und Jahreszeit geschichtet.

Overall, protective associations were strongest in urban areas, where an estimated 7,712 hospitalizations for mental health disorders per year could potentially be prevented through increased exposure to green spaces.

Seasonal patterns were also found in urban areas, suggesting that climate and weather conditions play a crucial role in the use and perception of green spaces, the authors say.

Further analysis in urban areas found that a 10 percent increase in green space was associated with fewer hospitalizations for mental disorders, ranging from about 1 per 100,000 in South Korea to about 1,000 per 100,000 in New Zealand.

As this is an observational study, no firm conclusions about cause and effect can be drawn and the authors acknowledge the uncertainties associated with using hospitalization data from multiple countries. They also point out that their results only capture serious illnesses requiring inpatient treatment and therefore underestimate the overall mental health burden.

Professor Guo said a significant proportion or rate of hospitalizations for mental disorders could be linked to exposure to green plants and could potentially be reduced by greening measures in realistic scenarios.

These mental health benefits can also bring broader economic and social benefits, including reduced healthcare costs, reduced burden on healthcare systems, improved workplace productivity and better community well-being.

Future research should aim to examine the differential impact of different types of green spaces, such as parks or forests, on mental health and focus on assessing the quality and accessibility of green spaces.

Yuming Guo, Professor, Monash University

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