A new ally to improve mental health

The mental health has become one of the biggest concerns of our time. Stress, anxiety, depression and emotional exhaustion They affect millions of people around the world, and although we know that exercise, adequate rest, social relationships and good nutrition help, it is increasingly evident that taking care of the mind requires a comprehensive and constant approach.

Now, a new ally joins that list of factors that can make a difference: the contact with nature. An international analysis maintains that Living or spending time in vegetated environments not only improves emotional well-being, but could also reduce the risk of hospitalizations for mental disorders. One more reason to understand that what surrounds us directly influences how we feel.

A global analysis with almost two decades of data

An analysis of data from seven countries over two decades of the Monash UniversityAustralia, published in the climate issue of ‘The BMJ‘, reveals that higher levels of vegetation are associated with lower risks of hospitalizations for mental disorders.

The results suggest that this protective effect increases with a greater exposure to green spaceswithout a clear threshold; evidence that can inform urban design and health policies to better protect mental health, researchers say.

Mental well-being remains a global challenge. It is estimated that 1.1 billion people suffered from mental disorders in 2021, contributing to 14% of the global burden of disease, with associated economic and social costs.

There is growing evidence to suggest that exposure to green spaces may reduce the risk of mental disorders, but most previous studies are limited to individual countries, short-term exposures, or specific mental health outcomes.

To address these gaps, researchers analyzed 11.4 million hospital admissions for mental disorders from 6,842 facilities in seven countries (Australia, Brazil, Canada, Chile, New Zealand, South Korea and Thailand) between 2000 and 2019.

No threshold: the greener the better

They included mental disorders of any cause and six specific categories (psychotic disorders, substance use disorders, mood disorders, behavioral disorders, dementia and anxiety).

Greenness was measured using the Normalized Difference Vegetation Index (NDVI), a widely used and reliable satellite-derived metric for assessing vegetation levels in a given area.

Factors such as population levels, climatic conditions, air pollutants, socioeconomic indicators and seasonality were taken into account, and the models were stratified by sex, age, urbanization and season of the year.

The results show that the Presence of local green spaces was associated with a 7% reduction in hospital admissions for mental disorders from any cause, with strongest associations for substance use disorders (9%), psychotic disorders (7%), and dementia (6%).

However, the associations varied by country and disorder. For example, Brazil, Chile, and Thailand showed consistent protective associations across most disorders, while in Australia and Canada, the presence of green space was associated with a slight increased risk of all-cause mental disorders and several specific disorders.

Overall, the protective associations were stronger in urban areas, where an estimated 7,712 annual hospital admissions for mental disorders could have been avoided through greater exposure to green spaces.

The authors state that seasonal patterns were also found in urban areas, suggesting that climate and weather conditions play a crucial role in how green spaces are used and perceived.

Additional analyzes in urban areas suggested that a 10% increase in vegetation was associated with a fewer hospital admissions for mental disorders, which ranged from around 1 per 100,000 population in South Korea to approximately 1,000 per 100,000 population in New Zealand.

This is an observational study, so definitive conclusions about causality cannot be drawn, and the authors acknowledge the uncertainties inherent in using hospital admission data from multiple countries. They also point out that their results only cover serious disorders that require hospitalization, therefore they underestimate the total magnitude of mental health problems.

An argument for redesigning cities

However, they state that this study suggests that “a considerable proportion or rate of hospital admissions for mental disorders may be associated with exposure to green spaces and could potentially be reduced by reforestation interventions in realistic scenarios.”

“These mental health benefits can also provide broader economic and social advantages, such as reduced healthcare costs, reduced pressure on healthcare systems, increased productivity in the workplace and increased community well-being.

Future research should aim to explore the differential effects of different types of green spacessuch as parks or forests, on mental health outcomes, and focus on evaluating the quality and accessibility of such spaces, they add.