Mental health and nature

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“Nature is doing her best each moment to make us well. Nature is but another name for health.” (From Henry David Thoreau’s journals, 1852)

When we spend time in nature, we feel more rested, balanced, and healthy. The American philosopher Henry David Thoreau understood this back in the 19th century, and it’s hardly breaking news today. Because Thoreau strongly believed in nature’s healing power for body and soul, he took a drastic step in 1845: he moved into a small cabin in the woods to live alone in the wilderness. Over 150 years have passed since Thoreau’s realization — yet one question remains unanswered: we still don’t fully understand why nature makes us healthy or the mechanisms behind it.

For decades, researchers in medicine, philosophy, and psychology have studied this phenomenon. In light of the climate and biodiversity crisis, this field of research is becoming increasingly important as our environments change so drastically. Time and again, studies show that “exposure and experience of nature” — in other words, contact with and immersion in nature — boosts our mental health and well-being, and that spending time in nature reduces the risk of many mental disorders, such as depression, anxiety disorders, or attention deficit hyperactivity disorder (ADHD).

Why is nature good for our mental health?

When we spend time in nature, it has an effect on many psychological levels. Negative emotions are dampened, positive emotions are enhanced, and stress is reduced. The forest, the greenery, and nature are, anthropologically speaking, our natural habitat. If we date the beginning of urbanization to the rise of the industrial revolution, humans have spent less than 0.01 percent of their species history in modern environments. Humans have thus lived over 99.99 percent of their time in natural environments. This discrepancy between the natural environment for which our physiological functions are adapted and the highly urbanized and artificial environment we live in today could contribute to the emergence of the “stress condition” in modern humans (Song, Ikei & Miyazaki, 2016). Epigenetically, we are fully adjusted to a life in nature, yet today we live in cities without green spaces, trees, or other natural elements. In these urban environments, we are exposed to unnatural influences like toxins and noise. At the same time, we do not come into contact with “good” bacteria, viruses, and fungi found in nature that promote our immune system and microbiome. The human organism has simply not adapted to urban life, and it remains questionable whether it ever will. This could, in turn, have negative effects on well-being and quality of life and contribute to mental disorders, such as depression.

Does this mean that we all (like Henry David Thoreau) have to move to the forest to become happy? No, fortunately not! In fact, studies show that with relatively small time investments, we can create large positive effects on our mental health. Payne, Loi & Thorsteinsson (2020) showed that just 20 minutes in a “natural environment” led to a significant reduction in stress levels. Other researchers have found that 30 minutes in nature resulted in a significant improvement in mood, well-being, mindfulness, and meaningfulness. Even a window with a view of a natural environment seems to lead to higher life satisfaction (Chang et al., 2020). Meredith and colleagues (2020) even showed that young adults showed improved mental well-being after a 10-minute walk in nature, compared to people in urbanized environments.

Although the time frames vary slightly from study to study, the consensus is that 10 to 30 minutes of nature per day is beneficial for mental well-being. The term “nature” is flexible: you don’t always have to go to the mountains or the forest. The effect can also occur in smaller green spaces or parks, or even from a window with a view of a natural environment. This positive effect of nature on mental health is most likely amplified if you engage in physical activity during this time or spend the time in nature with friends or family (Klaperski et al., 2019).

What does nature do to our brain? Neuroscientific approaches

The mechanisms in the brain behind these positive effects are discussed in neuroscience. Research is still relatively in its early stages, but even today, there are exciting explanatory approaches that will need to be explored in the coming years. One of the most obvious hypotheses is that green and blue spaces lower the stress level, thus temporarily reducing cortisol levels.

In addition to this stress reduction, neuroscientists also suspect that the brain is more likely to enter a "resting state" in nature. During this "resting state," we reflect on ourselves, recall the past, and plan for the future. Disruptions in the "resting state" have been linked in numerous studies to various mental disorders, such as depression, anxiety disorders, or ADHD.

However, scientists suspect that in addition to stress and the "resting state," there may be other neurological mechanisms that cause us to feel better when we spend time in nature. In a study by Kühn et al. (2022), they investigated how nature impacts our mental health. The researchers found that time outdoors led to structural changes in the gray matter of the prefrontal cortex. They observed that certain areas of the brain, important for our well-being, become more active when we spend a lot of time in nature. These exciting results might offer the first explanation for the positive effects of "forest bathing." Further research is needed here, but it remains intriguing!

Researchers have thus already gained a lot of knowledge. However, we still do not know how nature lowers cortisol levels, why the brain more often enters the "resting state" in nature, or why the prefrontal cortex looks different in people who spend a lot of time in nature. There are now numerous studies investigating whether these positive effects on mental well-being can also be induced in "artificial nature." For this, scientists showed participants pictures or films during an MRI scan or had participants take a virtual nature trip with a VR headset. Even this "artificial nature" had a positive effect on well-being, although much weaker than a walk in a real, biological forest. Visual and auditory stimuli, such as light, colors, and birdsong, seem to play a major role. In addition, there are certainly other sensory impressions that we may not consciously perceive but which likely play a significant role. Emulating these unconscious stimuli in a lab setting is and will remain a difficult endeavor, which is why the healing power of nature may remain a mystery for a few more years.

Mental health and nature: What does the environment do to our minds?

When we spend time in nature, we feel better. Henry David Thoreau knew this in 1852, and we know it today – even without large-scale scientific studies. What we still don't know is which factors exactly trigger these positive effects: Is it the reflection of sunlight in the clear stream water? Or perhaps the colors of the plant leaves dancing in the wind? Could it be the soundscape of a flock of birds or even the musty smell of the forest floor? Or is it perhaps the combination of light, color, sound, and scent? Much more knowledge needs to be created here, so that we can help those who don't, like Thoreau, want to live alone in the woods. Once we know which elements of nature have healing effects, we can try to intentionally incorporate them into the daily lives of others and improve their mental health. With a bit of luck, the cities of the future will bring humans and nature into harmony.

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