As the world population grows, accompanied by rapid industrialization, urbanization has come to the fore. Cities offer multiple advantages in terms of workforce and talent concentration, availability of goods and services within a limited radius, and high exposure to entertainment and recreation.
Unfortunately, cities are also associated with mental health issues, traceable to overcrowding, poor housing, increased commuting time, traffic blocks, crime networks, and undesirable peer pressure.
A new paper published in the Environmental Research Journal reassesses the impact of green spaces in countering some of this mental stress in urban areas.
Study: Green space exposure on depression and anxiety outcomes: A meta-analysis. Image Credit: Shark_749/Shutterstock.com
Greenery is an important natural resource, with its ability to detoxify the air, promote emotional well-being, and enhance physical and mental health. A green space is an undeveloped piece of land that is open to the public, including public parks, trees, plazas, and other forms of urban greenery.
Several pathways have been reported whereby urban green spaces lead to better health.
Pollution increases the risk of nerve damage, cardiovascular disease (CVD), systemic inflammation, and obesity. All these conditions are linked to depression and anxiety.
Oxidative stress is reduced, air pollution is relieved, and noise pollution is decreased by the presence of green urban spaces.
Further, green spaces encourage greater social interactions and physical activity, reduce the risk of obesity, relieve stress, and help people feel a greater sense of well-being and belonging, all of which mitigate the risk of low mood disorders.
Depression and anxiety plague over 550 million people worldwide, as reported by the World Health Organization. The former is due to a deficiency in certain neurotransmitters, leading to declining brain function, tiredness, and suicidal thoughts in severe cases.
Anxiety involves disrupted central and sympathetic nervous system function, shown in the form of abnormal behavior and unstable neurological symptoms.
Multiple studies have contributed to a distinct and growing body of evidence on the favorable impact of green spaces on mental health.
Despite this, little is known about the specific characteristics of green spaces that are most closely linked to better mental health in teenagers.
What did the study show?
The researchers looked at observational studies to integrate the findings, interpreting them in terms of the difference in perceived mood levels per 0.1 unit increase in normalized difference vegetation index (NDVI) and 10% increase in the percentage of green space.
The findings showed that an increase in green space proportion by 10% was associated with an approximately 4% reduction in the risk of depression but produced only a slight effect on anxiety.
Again, each 0.1 unit increase in NDVI was associated with a 7% reduction in the risk of depression, in smaller though not larger studies.
Interestingly, both meta-analyses showed stronger associations with mental health in smaller samples, with younger individuals, with a clinical diagnosis of anxiety or depression, compared to those who were diagnosed by scales.
The results were also more significant in more developed countries, though mental illness has a high prevalence in less developed countries.
What are the implications?
Providing more green spaces within urban communities, both locally and on a city-wide basis, could mitigate the mental health issues linked to urban life. For those already suffering from depression and anxiety, greater exposure to green spaces could help relieve the symptoms and reduce the severity of these disorders.
There was high heterogeneity between the studies, which makes the results less reliable than they could be.
However, the researchers do corroborate earlier studies such as those which showed that forest environments or urban parks were more suitable for urban dwellers, in terms of mental health than city streets.
A 2019 review also found that nature exposure had a quantitative association with low mood disorders, being among the earliest such studies.
Many scientists and therapists recommend forest bathing (‘Shinrin-yoku’) to prevent mental illness, and residents of city spaces that have greater exposure to green spaces are less likely to develop depressive symptoms and signs.
Horticulture therapy is another form of treatment based on gardening and other activities centered around plants, to relieve stress and promote mental peace and positive social interaction.
Further research on these associations should use standardized tools and methods, with proper adjustment for confounding factors.
Improving or preserving green space should be regarded as a promising intervention for public health.”