In the early 2000’s it was estimated that the average American spends about 93% of their life indoors [1]. The average time spent outdoors differs between California and Alaska by only 2 mins per hour, per person [1]. Therefore, it seems that it is not weather or daylight hours keeping us indoors, but Western culture and priorities.

It is also important to note that these estimates were made before a global pandemic and associated lockdowns encouraged many to stay inside, more. These estimates were also made before television streaming services and social media platforms took center stage in our daily routines.

This is all to say that it is not a coincidence that, as a population, Americans are becoming more stressed, more depressed, and more anxious [2].

There are statistical associations and scientific explanations for the links between inactivity and mental health, lack of sun exposure and mental health, and time in nature and mental health [3-5]. Below, we are going to dive into the latter.

Shinrin-Yoku or “Forest Bathing”

In Japan, there is a practice called shinrin-yoku. Shinrin means “forest”, and yoku, “bath”. Shinrin-yoku means spending time, taking in the forest through all of your senses. In some Japanese forests, there are trained forest therapists who guide forest bathing experiences based on physical and psychological assessment. 

If you don’t have access to a forest therapist, however, you can still practice the basic elements and gain benefits of forest bathing.

The basis of forest bathing is being present in the forest and noticing the aspects of the forest. What do you see, smell, hear, and feel on your skin? By paying attention to all of these neutral, calming elements, you can start to let go of stress and worries associated with technology, urban life, and social relationships.

Much like meditation, forest bathing is all about being present in the moment. You should turn off your electronic devices, you should not focus on a destination. If you aren’t in the mood to wander, or your “forest” is a park too small for hiking, you can still forest bathe sitting or standing in one place. Perhaps you like to practice yoga or tai chi. Those can be practiced while taking in the sensory offerings of a forest too.

Respect for the healing power of nature isn’t limited to Japanese culture. In modern Germany and Austria, adults often take part in a health practice or “Kur” that includes a break from work to focus on mental and physical health. A Kur is likely to include nature walks, swimming, and mud bathing, based on a doctor’s recommendation.

The Specifics: maximizing the benefits of being outdoors 

What is “nature”?

You do need a place with trees to forest bathe. Yes, just being in the sunlight can have a positive effect on your mood through vitamin D production and stimulation of the pineal gland. But, standing outside isn’t what we mean when we talk about the healing power of nature. 

To maximize the benefits of being outdoors, you really need to find a green space in “wilderness”. While the definition varies, generally, “wilderness” is a place with species diversity and little human intervention. Try, if you can, to choose broadleaf woods or parks that feature water and areas with significant biodiversity. These spaces have been linked with greater health benefits [6-8].

While sitting in front of “simulated nature” (or staring at photos or videos of a forest environment) can be somewhat calming when you are suffering from stress or burnout, it doesn’t elicit the same feelings nor the same biological response as the real thing [9,10]. 

How does it work?

Science can’t yet fully explain why being in the forest calms us, but it does, and there are many avenues through which it may be happening. One review cites 21 plausible pathways through which nature promotes human health [9].

One particular theory relevant to mental health and mood is called the attentional restoration theory (ART). It explains that our home and work environments have an excess of “bottom-up stimulation”. In those environments, we must choose to simultaneously ignore distracting stimuli and concentrate on other stimuli in order to complete our tasks. This type of voluntary focus is stressful in and of itself, and over time induces cognitive fatigue [10]. 

In contrast, natural environments do not demand our attention. They elicit “soft fascination” which refers to scene content that automatically captures attention and triggers feelings of pleasure. In other words, we don’t have to concentrate or focus to enjoy nature. You can rest while passively noticing the sound of leaves rustling, feeling humidity on your skin, or smelling fall in the air. 

ART suggests that spending time in nature actually restores our energy and ability to focus on a demanding task when we return to work or school [10].

Speaking of smelling the air, another calming factor may be the inhalation of aromatic compounds from plants called phytoncides. In the human body, phytoncides can reduce blood pressure, alter autonomic activity, and boost immune functioning, among other effects [9]. 

The air in forests, mountains, and around moving water also contains high concentrations of negative ions, which have been shown to lift a depressed mood [9].

How is this measured?

If you are a data-minded person, you may be wondering how this is measured. Yes, many studies on nature and mental health are based on surveys and self-reported serenity levels, but not all. 

Stress reduction can be measured quantitatively through levels of cortisol, other adrenal/stress hormones, and certain inflammatory markers in the circulation or saliva. Pulse rate and blood pressure are also often associated with stress level, when compared to a baseline, and these data are collected in some studies.

This is to say, there is hard science involved in these claims. 

A Japanese study from 2007 reported significant stress reduction in male college students after just 30 minutes of forest bathing [11]. Students were assigned to walk for 15 minutes and then sit for 15 minutes in either a forest or a city area. Compared to the city, those who walked and sat in the forest had significantly lower blood pressure, pulse rate, and salivary cortisol concentration. All biological markers of stress reduction.

A larger 2012 study showed circadian cortisol cycles (a person’s normal fluctuations in stress hormone levels) are significantly affected by the amount of time they spend in nature [12]. 

Are the benefits of forest bathing really just from exercise?

Not all. Although exercise is also a well-supported adjunct treatment for multiple mental health conditions, you don’t need to elevate your heart rate to receive benefits from time in nature. It really is about “just being”. 

In terms of quantitative data, one study showed that two, 2-hour forest walks on consecutive days increased the number and activity of natural killer T cells (beneficial immune cells with anticancer activity) by 50 and 56%, respectively [15]. Those activities remained significantly boosted for at least a month after returning to urban life [15]. Urban walks do not elicit the same effect.

We would be remiss not to mention the opportunity to double-dip the mood boost. While a forest bath isn’t about exercise, if you can walk or hike through your chosen wilderness space, walking also has a statistically significant, positive effect on the symptoms of depression [16].

References

1. Leech, Judith A., et al. “It’s about time: a comparison of Canadian and American time–activity patterns.” Journal of Exposure Science & Environmental Epidemiology 12.6 (2002): 427-432.
2. Elisabeth Dubois, M. B. A., and Xiaojun Jenny Yuan. “The mental state of Americans amid the COVID-19 crisis: How socially vulnerable populations face greater disparities during and after a crisis.” Journal of Emergency Management 19.9 (2021): 69-80.
3. Werneck, André O., et al. “Physical inactivity and elevated TV-viewing reported changes during the COVID-19 pandemic are associated with mental health: A survey with 43,995 Brazilian adults.” Journal of Psychosomatic Research 140 (2021): 110292.
4. Humble, Mats B. “Vitamin D, light and mental health.” Journal of Photochemistry and Photobiology B: Biology 101.2 (2010): 142-149.
5. Bratman, Gregory N., J. Paul Hamilton, and Gretchen C. Daily. “The impacts of nature experience on human cognitive function and mental health.” Annals of the New York Academy of Sciences 1249.1 (2012): 118-136.
6. Tsunetsugu, Yuko, et al. “Physiological effects of Shinrin-yoku (taking in the atmosphere of the forest) in an old-growth broadleaf forest in Yamagata Prefecture, Japan.” Journal of physiological anthropology 26.2 (2007): 135-142.
7. White, Mathew, et al. “Blue space: The importance of water for preference, affect, and restorativeness ratings of natural and built scenes.” Journal of environmental psychology 30.4 (2010): 482-493.
8. Aerts, Raf, Olivier Honnay, and An Van Nieuwenhuyse. “Biodiversity and human health: mechanisms and evidence of the positive health effects of diversity in nature and green spaces.” British medical bulletin 127.1 (2018): 5-22.
9. Kjellgren, Anette, and Hanne Buhrkall. “A comparison of the restorative effect of a natural environment with that of a simulated natural environment.” Journal of environmental psychology 30.4 (2010): 464-472.
10. Martens, DÖrte, and Nicole Bauer. “Do presentation modes of nature influence the effect on human well-being?: A comparison of laboratory and field results.” International Journal of Psychology 43.3-4 (2008).
11. Kuo, Ming. “How might contact with nature promote human health? Promising mechanisms and a possible central pathway.” Frontiers in psychology 6 (2015): 1093.
12. Pearson, David G., and Tony Craig. “The great outdoors? Exploring the mental health benefits of natural environments.” Frontiers in psychology 5 (2014): 1178.
13. Tsunetsugu, Yuko, et al. “Physiological effects of Shinrin-yoku (taking in the atmosphere of the forest) in an old-growth broadleaf forest in Yamagata Prefecture, Japan.” Journal of physiological anthropology 26.2 (2007): 135-142.
14. Thompson, Catharine Ward, et al. “More green space is linked to less stress in deprived communities: Evidence from salivary cortisol patterns.” Landscape and urban planning 105.3 (2012): 221-229.
15. Robertson, Roma, et al. “Walking for depression or depressive symptoms: a systematic review and meta-analysis.” Mental health and physical activity 5.1 (2012): 66-75.
16. Li, Qing. “Effect of forest bathing trips on human immune function.” Environmental health and preventive medicine 15.1 (2010): 9-17.