Why Forest Therapy Works

July 17, 2018



A growing interest in environmental stress has led me to seek hard evidence on how urban living is affecting our bodies, minds and spirits. The use of anti-depressive and anti-anxiety medications are skyrocketing in urban settings, a partial solution which doesn't work for everyone and isn't even available to many. When people seek alternative remedies for suffering, high-budget marketing can often skew the data and make it difficult to know what works and what doesn't. After hearing the term "forest bathing" many skeptics have asked me to evaluate its claims to heal people.


Challenge accepted.


Shinrin-yoku, (forest bathing, or taking in the forest atmosphere) was a term first coined in Japan in 1984 to describe the contact and experience of being in the forest. It is more than going for a walk or a hike. It describes a moving meditation, a deliberate communication with the environment and a conscious observation of its wonders.  Shinrin-yoku is said to promote lower concentrations of cortisol in the body, lower the heart rate and blood pressure, promote greater parasympathetic nerve activity, and lower sympathetic nerve activity than city environments. But does it really work? Can it be used as an effective strategy for prevention?


To find out, I've reviewed the literature from over 36 international studies which provide quantitative data on the relaxation effects induced by forest settings. The studies collected data on the physiological parameters related to stress. These included autonomic nervous system activity (heart rate, systolic and diastolic blood pressure, heart rate variability), endocrine system activity (salivary cortisol concentration) and immune system activity (salivary IgA concentration). This is what I found:


1. Walking in the forest lowers your stress hormones


Walking in the forest for just 40 minutes decreased levels of the stress hormone cortisol in test subjects, when compared with a control group of subjects who engaged in walks within a laboratory setting. High stress levels can play a role in high blood pressure, heart problems, kidney disease, diabetes, skin conditions, asthma, inflammation, and migraines among other illnesses. On average, individuals engaging in leisurely forest walks showed a 12.4% decrease in salivary cortisol levels when compared to their urban walking counterparts.


2. It has short and long term effects


Hormones are produced and circulated through the body via the complex endocrine system. This controls and monitors everything from hunger to panic attacks. It is the system that makes love and the system that makes war. The endocrine stress system is comprised of two broad components with considerable central anatomic interconnection, namely, the sympathetic adrenal-medullary (SAM) axis and the hypothalamic-pituitary-adrenal (HPA) axis.


Research suggests that both of the main components of the endocrine stress system reacted in response to Forest Therapy. The SAM axis is involved in immediate sympathetic activation. It prepares an individual to deal with a stressor, by creating changes such as increased heart rate and blood pressure. Cortisol is released by the HPA axis in response to the SAM axis and has long-lasting effects. While subjects viewed forest landscapes or walked around forest environments, their heart rate, blood pressure, and cortisol concentration decreased.


3. It boosts your immune system


Stress hormones compromise your immune system, particularly the front-line defender cells like natural killer cells, a group of innate lymphocytes (white blood cells) which respond rapidly to a wide variety of pathological challenges. You can see learn more about them here. Their activity is significantly reduced when cortisol levels are high. In a 2007 study, men taking 2-hour walks in the woods over a two day period exhibited a 50% increase in levels of natural killer cells.


Additionally, preliminary research is suggesting Shinrin-yoku may have anti-cancer benefits, although more research is needed. A 2008 study of 13 female nurses on a three-day trip, showed increased levels of anti-cancer protein production lasting more than a week after the trip.



4. It can help regulate your blood sugar


A Japanese study found that individuals who spent more time in the forest had lower blood sugar, improved insulin sensitivity, and decreased levels of hemoglobin A1c.


Researchers followed 87 adults diagnosed with type-2 diabetes for 6 years. They walked in the forest nine times in this period for 3 or 6 kilometers (1.9 or 3.7 miles), depending on their physical ability. Any form of exercise can help improve blood sugar regulation in people with diabetes. However, the frequency of the walks (only 9 times in 6 years) and the fact that blood sugar levels were significantly decreased regardless of the length of the walk, researchers concluded that the environmental factors related to the forest walks, apart from exercise, led to the positive long-term results, including changes in hormonal secretion and nervous system function associated with blood sugar metabolism.


5. It helps you concentrate


Researchers in the United States investigated the effects of outdoor green spaces on symptoms of attention-deficit/hyperactivity disorder (ADHD) in children and found its effects were comparable to those of Ritalin. In a randomized controlled study, doctors specializing in environmental psychology at the University of Illinois studied 17 children diagnosed with ADHD who were exposed to three different environments. After 20-minute walks in a park, children experienced substantially improved concentration compared to 20-minute walks in downtown and residential settings.


6. It reduces feelings of depression and anxiety, and can help you sleep better


When viewing a forest landscape, the low relative illumination reduces anger, and the low relative humidity lowers fatigue. Forests located at high elevations with low atmospheric pressure can reduce depression. The results of the physiological measurements suggest that activities like Forest therapy can aid in effectively relaxing the human body, and the psychological effects of forest areas have been correlated with the various physical environmental factors of forest.


The Profile of Mood States (POMS) is used to gauge the psychological response to forest  therapy treatments. The POMS consists of 30 adjectives rated on a 0–4 scale that can be consolidated into the following categories: T–A (tension and anxiety), D (depression and dejection), A–H (anger and hostility), F (fatigue), C (confusion), and V (vigor). Because of its responsiveness, the POMS have been widely used in the assessment of mood changes resulting from a variety of interventions.


Kasetani et al. reported that a relationship exists between the POMS score and the physical environmental factors. The POMS anger score lowered in relation to the illumination found in forested areas. The fatigue score and relative humidity showed significant correlation as scores in that category dropped in areas with low relative humidity. Finally, the POMS depression score and atmospheric pressure data showed lower feelings of depression and anxiety were reported in areas with low atmospheric pressure.


From the perspective of human evolutionary biology, human beings have lived predominantly in the natural environment for most of their existence. Their physiological functions are most suited to natural settings. Modern life often disconnects us from nature in ways which leave us feeling disconnected from ourselves, loved ones, and our bodies. The results of the physiological experiments conducted in this studies yield convincing answers explaining the relationship between the natural environment and the relaxation effects in a human being (e.g., decrease in blood pressure and pulse rates, inhibition of sympathetic nervous activity, enhancement of parasympathetic nervous activity, and decrease in cortisol concentration levels).


The research on Shinrin-yoku as medicine (Forest Therapy) shows that it works whether you think it's a gimmick or not. Open your mind and give it a try.





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