Scientific research provides powerful evidence of the importance of nature for our health. Time spent in the Great Outdoors reduces the stress hormone cortisol and increases our sense of well-being.
As Western society has developed, we have retreated from the Great Outdoors, placing greater importance on technological pursuits and human creations. Mounting scientific evidence reveals that by pushing ourselves away from nature, we not only have distanced ourselves from crisis-level environmental problems, but also have begun to lose contact with a vital mental-health tool. By denying ourselves time in green space, we risk rejecting an essential part of our heritage — a truth that, ironically, we are now able to see more clearly because of advances in medical technology.
Healers within various medical systems, from India’s Ayurvedic medicine to traditional Chinese medicine, have long advocated for the importance of nature. Indeed, in many cultures, it’s regarded as a form of medicine. But the notion that trees and flowers can influence psychological well-being remained largely untested in a scientific way until 1979, when behavioral scientist Roger S. Ulrich examined the mental influence of nature scenes on stressed students. His psychological testing showed differences in mental states and outlooks after the students viewed various environmental scenes. The nature scenes increased positive feelings of affection, playfulness, friendliness and elation. Urban views, on the other hand, significantly cultivated one emotion in these students: sadness. Viewing nature tended to reduce feelings of anger and aggression, and urban scenes tended to increase these feelings.
Encouraged by his findings, Ulrich set up a similar experiment to measure brain activity in unstressed, healthy adults. His team discovered that seeing natural landscapes was associated with increased production of serotonin, a chemical that operates within the nervous system. Almost all antidepressant medications are thought to work by enhancing the availability of serotonin for use in nerve cell communication, hence its moniker, “the happy chemical.” A follow-up study showed that green spaces acted as a sort of visual Valium: The nature scenes fostered positive thoughts, and lowered post-stress anger and aggression.
Many other contemporary researchers have used objective testing to support Ulrich’s pioneering work:
• In one study, older adults in a residential care center in Texas engaged in the same mental activities in two contexts — once in a garden setting and again in an indoor classroom. The participants were shown to produce lower levels of the stress hormone cortisol while in the garden.
• The presence of plants in a room, particularly flowering plants, can enhance recovery from the stress induced by an emotional video, quickly bringing brain wave activity back to normal, researchers at Kansas State University found.
• A research group from Taiwan reported that rural farm scenes are associated with higher alpha-wave activity, particularly in the right part of the brain, which has been linked with creativity. Forest scenes and natural water scenes promote alpha-wave activity and decrease heart rate. Conversely, an increase in muscular tension has been associated with city scenes.
Among the many reasons to preserve what’s left of our forests, the mental aspects stand tall. In 1982, the Forest Agency of the Japanese government premiered its shinrin-yoku plan. In Japanese, shinrin means forest, and yoku refers here to “basking in.” More broadly, it is defined as “taking in, with all of our senses, the forest atmosphere.” In 1990, Dr. Yoshifumi Miyazaki of Chiba University conducted a small test study of shinrin-yoku in the beautiful landscape of Yakushima, home to Japan’s most revered forests. Miyazaki found lower levels of the stress hormone cortisol in subjects after they took forest walks, compared with those who took walks in the controlled environment of the laboratory.
Since then, university and government researchers in Japan have collaborated on detailed investigations, including projects to evaluate physiological markers while subjects spend time among trees. These studies have confirmed that spending time in a forest setting can reduce psychological stress, depressive symptoms and hostility, while at the same time improving sleep, and increasing vigor and a feeling of liveliness. These subjective changes match objective results reported in nearly a dozen studies — that lower blood pressure, pulse rates and levels of cortisol accompany time spent amid trees and flowers.
Stress hormones can compromise our immune systems, particularly the activities of front-line defenders, such as antiviral killer cells. Because forest-basking can lower stress-hormone production and elevate mood, it’s not surprising that it also influences immune-system strength.
In 1984, Ulrich published a landmark study in the prestigious journal Science, in which he examined records for adults who had undergone identical gallbladder surgeries in the same hospital. The only major distinction among the patients was the room into which they were wheeled for recovery. Rooms on one side of the hospital had windows with a view to a mini-forest, while rooms on the other side offered a radically different vista of red bricks. The results were quite dramatic: Those who had an outdoor view of trees had significantly shorter hospital stays, fewer post-surgical complaints, and were able to manage their pain with aspirin instead of narcotics. Other studies have confirmed Ulrich’s findings. Among them:
• Norwegian research showed that having a plant at or within view of an office workstation significantly decreases the amount of sick leave workers take.
• Research published in 2008 in the Journal of the Japanese Society for Horticultural Science showed that greening select high school classrooms with potted plants significantly reduced the students’ visits to the school’s infirmary compared with the number of visits by students attending classes in rooms without plants.
World Health Organization projections indicate that in fewer than 20 years, 75 percent of the world’s population will live in urban settings, compared with the current distribution of about 54 percent city dwellers. The potential ability of a single factor — time in nature — to counteract a cascade of stress hormones will have enormous implications for us and future generations.
Because so many aspects of human health and even longevity are negatively influenced by stress, it follows that green space is a promoter of human health, vitality and longevity. Ample research confirms this. The closer your family lives to green space, the healthier you’re likely to be, and the longer you’re likely to live. Merely being in nature for brief periods — even just having it in view — can reduce the flood of stress hormones and improve immune defenses.
Critics once might have suggested that subjects who reported improved mood while viewing nature scenes were merely marking the right boxes that would fulfill the researchers’ expectations. The true, objective test would be the ability to go inside the brain and analyze it while it was focused on nature.
In the 1990s, researchers in California gained that ability by using functional magnetic resonance imaging (fMRI), a sophisticated brain-imaging technique. Their findings showed that aesthetically pleasing nature views fired up a specific portion of the brain that’s rich in opioid receptors. These receptors connect to the brain cells within the dopamine reward system, and carry the potential to trigger feelings of wellness and to propel the motivation required for positive behavior.
This was an incredible finding, revealing that nature is like a little drop of morphine for the brain. Although best known for pain inhibition, the opioid receptors do so much more. When these receptors are activated, people are less likely to perceive themselves as stressed, are more likely to form emotional bonds, and tend to dwell less on negative memories.
In two separate studies, Korean researchers used imaging to assess brain-activation patterns while subjects viewed urban or nature-based scenery. In the first study, viewing the urban scenes resulted in pronounced activity in the amygdala, a center in the brain most often associated with feelings of fear. Overactivity of this center has been linked to impulsivity and anxiety. Furthermore, chronic stress and cortisol may promote activity in the amygdala, and in this overactive state, we tend to selectively prioritize the memorization of negative events and experiences. This becomes a vicious cycle: The world looks a bit more scary and depressing, and our dominant memories confirm that to be true. When the amygdala is amped-up on a regular basis, it fuels the brain’s fear. The good news is that we can regain control by acknowledging our thought processes and seeing green — placing ourselves in environments that will dial down the fear.
When large population studies indicating a stress-buffering effect are layered on top of studies using subjective and objective evaluations of mood and stress — and when this information is, in turn, layered onto hospital data and brain-imaging studies — the picture of nature’s influence emerges. Add to this body of information dozens of forest-basking studies from Japan, the argument that time in nature has no consequence on human health and physiology becomes impossible to support.
The results of these scientific investigations should wake all of us up to the importance of preserving nature. The wellness of individuals and nations — and clearly the planet — depends on recognizing the importance of nature to human health.
Research has shown that pleasure and happiness are elevated as tree density increases. The bigger and denser the trees, the better the scenic beauty scores — up to a point. If trees are too tightly packed — if a trail is too narrow or obscured — the scene becomes foreboding and causes fear.
Lining one’s walls with wood might be too much of a good thing. Japanese researchers have found that the sweet spot for the right amount of wood on the floor and walls is somewhere between 30 and 40 percent of surface area. If you go all-out and panel the entire room, your stress can actually increase.
Dr. Eva M. Selhub is a clinical associate at the Benson-Henry Institute for Mind Body Medicine at Massachusetts General Hospital, and an instructor at Harvard Medical School. Alan C. Logan is a naturopathic doctor, scientist and independent researcher. This article is based on an excerpt from their book, Your Brain on Nature: The Science of Nature’s Influence on Your Health, Happiness and Vitality.
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