Research shows that spending time in natural settings protects against a wide range of illnesses—including depression, diabetes, obesity, ADHD, cardiovascular disease, some cancers, and more. For years, the mechanisms behind these health benefits remained unclear. After reviewing hundreds of studies on nature’s effects, Ming Kuo, an environment and behavior researcher at the University of Illinois, argues that many of nature’s health benefits flow through improvements to the immune system.
Kuo examined dozens of studies and identified as many as 21 plausible pathways linking contact with nature to physical and mental health. Remarkably, she found that most of these pathways share a common element: they are connected to immune functioning. This observation helps explain why exposure to green space appears to protect against such a broad and diverse set of conditions.
“I gathered every piece of research in this area that I could find,” Kuo says. “I was surprised to see 21 possible pathways, and even more surprised to notice that nearly all of them converge on the immune system. That suggests the immune system plays a key role in how nature supports our health.”
Kuo likens nature’s effects to a multivitamin: it does not contain a single active ingredient but instead provides many complementary benefits that together improve overall health. Because these benefits span cardiovascular, respiratory, mental health, and musculoskeletal outcomes, a broad, systemic mediator such as the immune system makes conceptual sense.
A simple model helps make sense of these findings. Time in nature often reduces perceived threat and increases feelings of safety and relaxation. That relaxed state activates the parasympathetic nervous system—the so-called “rest and digest” mode—which in turn frees the body to invest resources in long-term maintenance, growth, and immune readiness. By contrast, chronic stress and repeated activation of “fight or flight” responses divert energy away from immunity and other restorative processes.
“When we feel safe and at ease, the body can allocate resources toward building and maintaining the immune system,” Kuo explains. “Nature appears to provide cues of safety and calm that allow those restorative processes to take place.”
Kuo also notes that some indoor activities can offer partial benefits. Activities that absorb and relax people—such as playing board games, reading, or visiting an art gallery—can engage the parasympathetic system and support immune-related gains. However, indoor pastimes typically lack many of the exterior elements that nature supplies: phytoncides (plant-emitted compounds), soil-derived microorganisms such as Mycobacterium vaccae, negative air ions, and vitamin D–stimulating sunlight. Because those outdoor “active ingredients” are absent or diminished indoors, the immune and health boost from indoor experiences is likely to be smaller.
Kuo directs the Landscape and Human Health Laboratory at the University of Illinois and has conducted multiple studies linking green space to health outcomes. By compiling and synthesizing results across disciplines, she aims to provide a clearer research agenda and point toward the most promising mechanisms for future study.
“Identifying the immune system as a primary pathway helps answer how contact with nature and the human body work together to resist disease,” Kuo says. “This perspective also offers testable hypotheses for researchers and practical implications for public health and urban design.”
Her comprehensive review appears under the title “How might contact with nature promote human health? Exploring promising mechanisms and a possible central pathway,” published in Frontiers in Psychology. The paper outlines the 21 candidate pathways, sets criteria for identifying a central pathway, and argues that enhanced immune functioning is a promising central candidate—while acknowledging there may be other central mechanisms as well.
Source: Debra Levey Larson – University of Illinois
Image Source: Image credited to NeuroscienceNews.com
Original Research: “How might contact with nature promote human health? Promising mechanisms and a possible central pathway” by Ming Kuo, published in Frontiers in Psychology. Published online August 25, 2015. doi:10.3389/fpsyg.2015.01093
Abstract
How might contact with nature promote human health? Promising mechanisms and a possible central pathway
Numerous studies link contact with natural environments to better physical and mental health. This review compiles 21 plausible pathways that connect nature to health outcomes, spanning environmental exposures, physiological and psychological states, and behaviors. The paper proposes criteria for identifying a possible central pathway—one that can account for the size and specificity of nature’s health effects and that can subsume other pathways. Applying those criteria, enhanced immune functioning emerges as a promising central pathway that may help explain how diverse health benefits arise from nature exposure. While immune enhancement is highlighted as a compelling candidate, other central mechanisms may also exist and warrant further study.