Back to the Forest: The Health Benefits of Shinrin-yoku

You may have been witness to a developing phenomenon in your local park. It may be a small group interacting with nature, touching bark and moss, smelling the air as they huddle together, sitting down meditating or making yoga poses in the park. What is this action? Is it a rebirth of the seventies? You may be surprised that as you meander along a path in the park or just sit outside listening to the river or birds calling, you are doing the same thing – Shinrin yoku’ or forest bathing. The benefits of this practice are myriad. The post will summarize these benefits and hopefully after reading this, you too might wish to contemplate the message in a nearby park.

Techno Mental Toil (TMT)

Modern times call for us to interface with networks, all of which can become our tethers. Whether it’s multiple text message beeps, phone calls sending auditory and vibratory signals, a computer screen where much time is spent staring, we increasingly look away from what is outside of us. We are in constant contact yet further away than ever, as we bring our smart phones wherever we go — even in the woods. I ocassionally see people hiking in the park, as they talk on the phone, broadcasting their complaints or concerns to passing hikers and drowning out the sounds of birds calling.

In a world where we can connect online at any time, we have the hardest time to disconnect and be in the “now” as an observer in nature. Rescue time found that the average user (among 11,000) spent 3 hours and 15 minutes on their phones daily – with some estimates of total daily screen time up to 11 hours. It wasn’t just the screen time but the frequent checks, up to 58 times a day, that decrease productivity and cause our minds to shift off-task and dumbing us down. These stimuli signal to our brain in different ways to modulate our moods through floods of dopamine, epinephrine and norepinephrine.

Our children are taking after these habits. The Kaiser family foundation estimates that children between 8 and 18 spend an average of 7.5 hours a day in front of a screen. These children aren’t playing outside while they are in front of screens. The fact that my youngest son once tried to convince me that watching a nature program was the same as going on a hike in the park says it all. What a creative rebuttal to my constant attempts to corral “the gang” for a walk in the park! As I unplug my children from their devices (now less painfully with an automatic wi-fi shut-off!), I am abundantly supported by science that this is the very thing that is needed for our own and our children’s health – body, mind and spirit, including creativity.

Enter Shinrin-yoku

Any parent has observed that when children are out in the woods, they often forget the time. They shift their attention from the past and the future and “plug” into the now. They play with rocks, turn them over to see what is underneath, imagine another world in the woods and truly interact with what is in front of them – the smells and the sounds included.

Shinrin-yoku from the Japanese “forest” and “bath” has became one of Japan’s public health initiatives in the 1980s after extensive testing confirmed that sensory immersion into wooded areas was beneficial for a range of medical conditions. It refers to simply spending time outside in nature. It is not surprising that this movement originated in the paradox that is Japan, with its Tokyo businessmen at risk of karoshi, “death by overwork”, and with its ancient ties to nature in Shintoism. From incorporating this into national parks to developing an evidence-base on its health benefits, Japan has brought forest bathing to the world’s attention.

A large research initiative on forest bathing has been undertaken in Japan and other countries. A search on pubmed finds 110 articles on “forest bathing” or “shinrin-yoku”. These numerous studies support the benefits of sensory immersion into these natural environments on all aspects on our health. Japan has taken a precident with a governmental certification through scientific evaluation on the health benefits of a specific forest to become a Therapy Forest. In Japan and other countries, doctors are beginning to “prescribe” a dose of forest bathing, for its therapeutic effects on physical and psychological wellness.

How to Forest Bathe?

The easy answer to this is that there is no single right way to forest bathe. Simply spending time in the forest will expose one to the therapeutic effects. While there is plenty of reason to practice yoga, meditate or exercise outdoors, no extra activity or treatment is necessary to experience the positive effects of Shinrin-yoku. Whether in repose or walking through, participants take in the forest around them using all five senses. 

Some examples of forest bathing include:

  • Spending contemplative time sitting in the woods, listening to nature’s sounds
  • Exploring the senses – touching various textures; smelling flowers, wood, leaves and soil; seeing the subtle and more significant movement of the trees and leaves in the wind, the movement of birds, squirrels and other animals; hearing the sounds of that movement, bird calls and other animals; tasting the berries and other edible plants.
  • Taking a hike into a more remote area, or
  • Just walking on a short hike alone or with others.

Health Benefits of Shinrin-yoku

Geographical scientist Guan Haoming and his partners noted in 2017 that less than 0.01% of human history has been lived in urban society, so “people’s philological function is still better adapted to natural ambient.” While that study was exploring nature therapy to counteract the effects of smartphone use on teen anxiety, others have found it effective at improving cardiovascular and immune system health, treating depression, and even reducing blood glucose levels in diabetes patients.   Aspects of Shinrin-yoku have been incorporated into other practices and treatments as well, from wilderness therapy for troubled youth to gratitude and mindfulness practice in addiction recovery programs. While there is some debate on proper ‘dosage,’ Margaret Hansen’s review of Asian studies indicates that positive differences can be measured within as little as “5–7 [minutes] of each nature experience,” while others recommend 30-minute sessions to reap the most benefits.

Besides the more subjective changes in our psyche and emotional state (more about that later), there’s a lot going on at a molecular and cellular level when we step outside. First, if it’s daytime, our bodies are receiving the energizing and immune-boosting effects of the sun’s ultraviolet(b) rays. Like our cohabitants the plants and photosynthesis, humans require the sunlight as well – namely for conversion of a provitamin D3, a cholesterol synthesized by our skin, to previtamin D3 which is then processed by the liver and the kidneys to become active vitamin d3, calcitriol. A person can take mega-doses of vitamin d3 supplements, yet become deficient without enough sunlight. Second, regular exposure to sunlight also provides the zeitgeber (or time cue) to the human body’s almost 24 hour circadian rhythm. Sunlight triggers serotonin production in the retina to promote a wakefulness state, until nighttime comes and melatonin is produced. By adhering to these cues, it easier to fall asleep at night, which in addition to serotonin is also vital for regulating mood. 

As for the natural environment, plants and trees contain (and give off) certain protective chemicals called phytoncides and terpenes that we breathe in and absorb. Phytoncides have been found to stimulate the production of white blood cells, known as “natural killer” or NK cells, which literally kill unhealthy cells, such as those affected by cancer cells or a virus. Breathing phytoncides reduces the stress hormones adrenaline and noradrenaline, which researchers believe contribute to increased NK activity.  

Somewhat similar to phytoncides are terpenes, which are produced by plants, trees and some insects, and have various functions from fighting bacteria to attracting pollinators. They give plants their strong scents, and provide the building blocks for saps, resins, and essential oils used in medications, ointments, and aromatherapy. Essential oils are absorbed through the skin or olfactory system and can penetrate the semi-permeable membrane of cells and possibly have a biological effect. Different varieties are known to produce a range of effects; for instance, alpha-pinene (found in pine trees) promotes alertness, while linalool (lavender) is calming. Aside from some effect from their pleasant odors, terpenes and derivative substances may exhibit some antioxidants, anti-inflammatory and antibacterial properties – though further research models are needed.

Finally, natural environments provide better air quality, increasing oxygen flow to the brain, blood, and muscles while also improving respiration. Leaves absorb carbon dioxide and other particles (carbon monoxide, formaldehyde and benzenes) in the air for photosynthesis and release oxygen in the air as a byproduct of synthesizing sugar. Forest bathers are exposed to this air replete in oxygen.

Rx: Nature. More on the health benefits 

Just as the “park prescription” phenomenon is overtaking the US; and “earthing” to ground yourself has taken root with New Age spiritualists; Shinrin-yoku as a medical or therapeutic treatment is gaining both popularity and legitimacy among scientific researchers and medical professionals alike as field studies and clinical trials consistently produce positive results.   From small-group studies to meta-analyses (multiple comparable studies), the research indicates Shinrin-yoku is an effective way to combat hypertension and cardiovascular disease, diabetes, hypertriglyceridemia, ADHD, anxiety and depression and more.

Cardiovascular Health 

A Japanese systematic review of 20 trials in 732 participant showed significant reductions in both systolic and diastolic blood pressure readings from forest bathing. In a Lithuanian trial, one week of 30-minute park sessions improved cardiac function in Coronary Artery Disease patients. In Japan, healthy male subjects showed “significantly reduced blood pressure and urinary noradrenaline” levels after walking in a park forest when compared to walking in urban Tokyo. A study of 26 office workers showed a reduction in blood pressure and heart rate for up to five days after one day of forest therapy.  Even neighborhood parks and green spaces in urban environments have as much health efficacy for people as actual forests. For example, in a Finnish study, healthy participants exhibited lower blood pressure and heart rate, and higher heart rate variability (an indicator of the parasympathetic nervous system, which counteracts the body’s stress response and is associated with healthier heart functioning) after sessions in either forested or park environments, as opposed to downtown Helsinki.

Metabolic Disorders

In a longitudinal study of 48 adults diagnosed with Type II Diabetes, Y. Ohtsuka and others at Hokkaido University School of Medicine in Sapporo, Japan found blood glucose and glycosylated haemoglobin decreased (from 6.9 to 6.5) after short- (3km) and long-distance (6km) sessions of Shinrin-yoku. They posited that since Shinrin-yoku reduces cortisol levels reducing insulin sensitivity, the effects went beyond caloric expenditure.

One study showed elevations in the level of serum adiponectin, produced by adipose tissue, as a result of forest bathing. Lower levels are associated with metabolic syndrome, diabetes, cardiovascular disease and obesity, suggesting that forest bathing promotes a protective effect on these conditions.

The Endocrine system, Stress states, Mental Health and Addiction

Cytokines are proteins that are produced during inflammation. They are activated as part of an acute stress response, infection or other insult. When overproduced in chronic stress or disease states, the prolonged inflammation has a negative impact on the body. The body’s ability to fight infection and heal wounds is hampered. Chronic stress and inflammation can contribute to mental illness, diabetes, neuropathic pain, heart disease, osteoporosis, and autoimmune disorders. Mao and colleagues studied a group of 20 healthy participants and sent 10 on a 2 night trip to an evergreen forest, while the other 10 went to a city area. The markers of inflammation that were tested (interleukin-6, malondialdehyde and tumor necrosis factor) were decreased in the forest group compared to the city group. The forest appears to reduce inflammation.

Stress hormones like adrenaline and cortisol can also be toxic if allowed to persist in the bloodstream. A 2018 review article of non-laboratory studies by Kondo et al. reviewed 18 studies that measured salivary cortisol levels before an after a forest exposure. Eleven of these studies showed a significant decrease of salivary cortisol levels after forest bathing. Other measurements such as using anthropometric instruments, body fluid tests (saliva, blood, urine), self-report, actigraph and EEG to measure stress found evidence, particularly with heart rate, blood pressure and self-report, that green space reduces stress and ultimately improves health.

Shinrin-yoku and related activities involving immersion in green spaces have been shown to have calming effects both subjectively and at the endocrine level, and this has profound implications for some at-risk populations. Morita et al in 2007 showed that a forest day significantly reduced hostility and depression and increased liveliness, especially in those with chronic stress. Children with more severe attention deficit disorder have few medical treatment options because of the risk of abuse or overdose associated with traditionally-prescribed stimulants like methylphenidate (e.g Ritalin) can be significant. Studies have suggested that green space time may reduce symptom severity of ADHD and support the need for more randomized trials to better determine the effect.

Veterans in a substance abuse treatment program in Virginia found benefits to addiction recovery in the autonomy and direction of tending to a garden. Forest bathing also alleviated depression and aided recovery among alcoholics. In a study of 92 participants with treatment and control group, there was a significant improvement in pre- and post-test Beck Depression Inventory.

Applications 

Some practical applications of forest bathing are already being implemented in the United States. Although there is still no government-certified program in the US like there is in Japan or South Korea, a growing number of forest therapy guides (many of them doctors themselves) have completed certification from the international Association of Nature & Forest Therapy Guides & Programs. These guides follow certified programming that typically includes an invitation to explore and immerse oneself during a walkthrough at a nature park or reserve, and group discussion afterwards.   Additionally, outdoor behavioral healthcare treatment programs like Adventure Therapy and Wilderness Therapy utilize elements found in Shinrin-yoku in treating patients for anxiety disorders, substance abuse, and other maladaptive or dysfunctional living patterns. Forest bathing specifically has begun to be offered as a treatment modality at recovery centers in both North and South America.

Conclusion

Shinrin-yoku, or even just conscious outdoor activity in a natural or green space clearly promotes wellness. As a preventive measure, regular forest bathing may help to keep our hearts conditioned, optimize our immune system, manage mood and stress, and detox our brains and bodies of harmful chemicals. As inflammation is associated with autoimmune conditions and cancer, any activity that reduces inflammation might reduce the risk of these conditions.

Treatment options vary depending on the condition being treated and type of green space available, but perhaps that is what’s most valuable about this growing body of research – eco-therapy can be practiced anywhere, and improves symptoms for a wide range of mental and physical health conditions, making it a viable supplementary or alternative treatment for vulnerable populations all over the globe. 

Nature and Our children

In many ways, we as humans are evolving into indoor troglodytes. The new generation of youth are given cell phones on average when they reach 12 years of age, an important stage in development of social skills and coordination. Its mind-blowing to imagine that the average child spends less time outdoors than the mandatory 2 hours a prisoner gets – one third of children spends less than 30 minutes outside. In his bestselling book Last Child in the Woods, Richard Louv writes about the factors that contribute to what he calls “nature-deficit disorder” in children. Nature was a source of imagination and creativity – and of untamed beauty- as for the artists, poets and explorers. Even as a child, I remember my brother and I were encouraged to go outside and discover, sometimes taking trips in the ravine that connected to the natural parks near my childhood home.

What children can do outside can offer refuge, a sense of exploration and creativity, and a way to gain confidence. As the suburban sprawl expands into the forested lands and the computer interfaces become even more tantalizing – what will become of our children and their health?

Thanks for reading. A patient education form will soon follow. If you enjoyed this article, please pass it along.

Dr. Cirino conducts Shinrin-yoku walks on second and fourth Fridays as well as seminars on heath and wellness. Join him on meetup at Your Health Forum.

Suggested Reading:

Carr, Nicholas. The Shallows: What the internet is doing to our brains.

Li, Qing. Into the Forest. How trees can help you find health and happiness.

Louv, Richard. Last Child in the Woods. Saving our children from nature-deficity disorder.

Williams, Forence. The Nature Fix. Why nature makes us happier, healthier and more creative.

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4 thoughts on “Back to the Forest: The Health Benefits of Shinrin-yoku

  1. WOW! Thanks for this valuable information, Chris.
    Now I’m even more grateful I could participate w/you and my friend, Tara, in this healing, nourishing activity this morning!

  2. Yes, thanks, Chris! Very interesting! This confirms what most people know instinctively, that being outside in nature makes us feel good!

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