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People enjoying an urban park. Researchers are trying to understand the mechanisms at play that link improved human well-being to contact with nature.

Most people agree that time in nature is good for our mental and physical health. Whether it’s a remote wilderness backpacking trip or 15 minutes spent sitting on a park bench, people tend to feel better if they have some interactions with nature. 

Many scientific studies confirm this as well. Over the past two decades, and especially in the last few years, researchers have increasingly documented the positive effects of natural spaces on mental health and well-being. This includes outcomes like feeling less lonely, lower levels of burnout and depression and better abilities to cope during stressful situations. 

Now researchers are trying to figure out the mechanisms at play that link improved human well-being to contact with nature. In other words, what’s happening inside of us that causes us to respond positively to nature, sometimes without us even knowing it? Understanding these pathways could have implications for improved mental health, more intentional urban planning, and tools for helping individuals get more well-being benefits from nature.

“The more we can learn about how aspects of nature affect our minds and bodies, the more we’ll understand why these effects and associations exist, and why they have been observed in many different studies,” said Greg Bratman, associate professor in the UW School of Environmental and Forest Sciences and director of the Environment and Well-Being Lab. “This is important to know for a variety of reasons, including effective tailoring of a nature intervention or informing decision-making about how to integrate nature into cities and conserve open space — where it exists, how to maintain it, and what types of contact with natural environments matter most for people’s well-being.”

In a recent paper published in the journal Trends in Cognitive Sciences, Bratman and his colleague James Gross of Stanford University highlight a variety of promising directions this research is headed, led by dozens of researchers around the world. Bratman’s lab at the UW College of the Environment is pursuing research projects in some of these areas as well.

“We and others in the field are asking, why do different kinds of nature influence a range of individuals or populations in different ways?” Bratman said. “In order to more fully understand that, we need to know more about the mechanisms underlying these effects.”

There are likely many reasons nature contact improves our well-being. In their paper, Bratman and Gross focus on five possible mechanisms that may drive this, and share examples of research to back it up. They acknowledge this list isn’t exhaustive, does not include certain perspectives of human relationships with the natural world from some communities around the world, and that the field continues to evolve rapidly.

Mechanisms 1 and 2: Sleep and physical activity

Both sleep and physical activity have been proven to benefit mental health and well-being. Recent studies suggest that green spaces actually encourage more physical activity, and exercising outside might contribute more positive benefits than exercising indoors. For example, a recent study compared the results of walking in natural, urban and indoor spaces. Participants who walked in natural spaces found the experience more restorative and enjoyable than those walking in urban or indoor spaces. 

Similarly with sleep, new studies are finding that nearby nature likely plays a role in sleep health. One study found associations between living close to green spaces and getting better sleep. Another found that over four years and for nearly 20,000 participants, those who lived within 50-100 meters of green spaces had fewer sleep difficulties.

Mechanism 3: Emotion regulation

Another way that nature may affect our well-being is through emotion regulation. A growing body of research has found that time in nature may influence our patterns of thought, or change how we consider our problems. Knowing this, we may choose to engage in specific situations in nature or intentionally visit natural locations that make us feel better and help us self-regulate. For example, in one study people chose to visit their favorite places at least in part to reflect and experience positive emotions. Other studies have found that time in nature cuts down on rumination — a cycle of repetitive, negative thinking about the self.

Mechanism 4: Our immune system

Another line of research is looking at how nature can affect our immune system. The emerging field of psychoneuroimmunology supports the notion that psychological stress can trigger inflammation in the body, and that this inflammation can have impacts on well-being. In some cases, our brains interpret this increased inflammatory activity as a signal that can lead to states of anxiety, negative mood and social withdrawal.

Recent research supports a link between harmful environmental factors like air pollution and a chronically-activated immune response. On the flip side, other studies have found that some elements of nature may have a beneficial effect on our immune responses. For example, some “forest bathing” researchers are investigating whether phytoncides — volatile organic compounds released by trees — can potentially influence immune function and have anti-inflammatory effects through smelling and inhaling these molecules. 

Mechanism 5: Our microbiome

Finally, there’s growing evidence that time in nature may change our microbiomes — the communities of microbes living in our gut, nose and skin. Interactions with soil, eating certain plants or inhaling airborne microbes from nature could all play a relevant role in these shifts in the diversity and community composition of our microbiomes. This has repercussions for well-being, as certain bacterial communities in our bodies have been associated with stress, anxiety and depression. Preliminary work suggests that spending time in nature may potentially increase the presence of some of these beneficial microbes that live within us. In a recent pilot study, Bratman’s lab found that study participants who resided for eight weeks in a remote, forested location reported greater improvements in mood and decreases in rumination compared with participants who resided in a city for the same period. Additionally, after eight weeks the forest-dwelling participants had higher bacteria diversity in their nasal microbiome than the urban group, including the presence of certain taxa of bacteria previously associated with benefits for human well-being.

While this work is in the early stages, Bratman is excited to see experts across many fields — including atmospheric chemists, experts in olfaction, microbiome researchers, ecologists, exposure scientists, psychologists, and more — come together to push this research forward.

As the global population continues to move to cities — projections show that around 68% of people will live in urban areas by 2050 — this will bring both benefits and harms to mental health and well-being. Concurrent with this urbanization trend is a decrease in the amount of regular nature contact that many people experience on a regular basis. 

Bratman’s lab works to understand the implications of this shift in our daily experiences and contact with our surroundings, and increase insight into exactly how nature influences our well-being. He believes this can help us effectively design and integrate natural features within cities — and inform decisions to conserve nature outside of them — in ways that help to promote human well-being. 

“Along with understanding these and other mechanisms and effects, it is important to support efforts that aim to make nature more accessible for all, from urban greenspaces and views of lakes and oceans, to open space near city limits, to large and awe-inspiring national parks and landscapes around the country and world,” Bratman said. 

This work is supported by the Walker Endowed Professorship, the JPB Environmental Health Fellowship, John D. Miller, and Craig McKibben and Sarah Merner.

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Story by Michelle Ma. All photos are from Unsplash (creative commons license).