An easy way to gauge whether something is stressful is to measure cortisone levels. Cortisone, the “stress” hormone, is released during tense and stressful situations. My drive to work is apparently one of the most stressful parts of my day as it shoots my cortisone (and blood sugar) through the roof. As discussed before, chronic stress does some damage by repeatedly raising this hormone, but acute stress is actually healthy for us. Recently, I have found myself retaliating when chronic stress strikes with forest bathing. But are there actual health benefits from forest bathing?
Forest Bathing for Stress
I have always assumed that walking in the forest, or even living near green space had some benefits on my health. However, recently more and more studies are revealing the physiologic and biochemical benefit of these simple activities. For instance:
- Simply having more green space in your home helps to reduce stress and cortisol levels.1
- Senior citizens living in an urban environment with access to green space seem to live longer than those without it, independent of their baseline functional status.2
Urbanites – myself included – seem less likely to seek out parks and nature and are better served by bringing green space into their homes and offices.3 I would have to agree with this study as we often talk about going to the giant 644 acre park nearby to bathe in its greenness, but more often find ourselves walking around the city with our dog.
The anti-stress benefits of walking in nature are obvious, and I do not need to be up close and personal with the smell of oak trees and chirping birds to recognize these. How often do you leave the forest feeling anything but refreshed? Not surprisingly, the bulk of the data on forest bathing reveals significant mental health benefits.4 I immediately feel better. But what happens on a physiologic scale?
Besides the small reduction in cortisone, are any other changes happening deep inside my body?
The Similarities Between Forest Bathing and Eating Your Veggies
One of the most significant benefits of foods like spices and cruciferous vegetables is their ability to safely “stress” our cells, signaling to them to put up their defenses against invaders like infections and cancer. The result is a stronger immune system that is more capable of fighting foes and harmful free radicals. Surprisingly, forest bathing may have similar benefits.
When Bum Jin Park, from Chiba University in Japan, and his colleagues ran field experiments in 24 forests across Japan, they realized that the benefits of time in the forest were more than simply psychological. What they found was that Shinrin-yoku, or the act of “taking in the atmosphere of the forest” had far-reaching effects. In 280 individuals, walking through and viewing a forest versus a city led to lower concentrations of cortisol, heart rate, and blood pressure, and greater overall parasympathetic nervous systems (think the opposite of adrenaline and fight or flight).5
However, upon digging deeper, several chemical aspects of the forest may be responsible for the health benefits of forest bathing. Much like tannins in wine and sulfur in broccoli, terpenes are chemicals that help protect many plants from predators, like animals and microorganisms.6 Some common terpenes are mentol and camphol, the aromatic component of many essential oils. Another one named limonene smells like – you guessed it – lemons. Pine trees, cedars, spruces, and conifers in general are some of the largest producers of terpenes. Furthermore, much like the tannins in wines, the terpenes provide a pleasant, yet almost bitter, taste and smell that trains our immune system and promotes antioxidant defense.
Does simply breathing them in help? It’s unclear. We know that the lemony aura of limonene is more than just a scent, as it can be found in our blood after exposure.8 Furthermore, several anticancer cellular pathways appear to be affected by the terpene limonene, leading some to suggest it has anticancer, or chemopreventative, benefits.9 While feeding it to rats in studies has revealed some efficacy against breast tumors,10 we have a ways to go before we can make such bold claims in humans. It does, however, appear to increase detoxification mechanisms to reduce carcinogen exposure in animal studies.
Another terpene, α-pinene is released by plants as a volatile defense mechanism, yet seems to decrease inflammation by inhibiting NF-κB (Nuclear Factor Kappa B).11 NF-κB regulates our immune response and is turned on in response to harmful states like infection. Too much NF-κB, however, is linked to an increased risk of cancer and autoimmune disease. Exposure to linalool, a terpene found in flowers and spice plants, decreased inflammatory damage in the lungs of smoke-exposed mice.12 Linalool is found in lavender and basil, and in keeping with terpenes ability to defend against plant prey, is used by exterminators as an insecticide.
Like NF-κB, several other cellular pathways are effected by terpene and plant chemicals. MAPKs (Mitogen-Activated Protein Kinases), which help the cell to respond to stress and inflammation, are vital in nature, but also regulate gene expression and survival. Both are vital to immortal cancer cells. IL-6, when not secreted by our exercising muscles, is an inflammatory protein, and TNF (Tumor Necrosis Factor) is another inflammatory protein intimately linked to cancer. TNF also causes the severe muscle wasting, known as cachexia, that is often seen in cancer patients. The body releases these inflammatory factors to help fight cancer, but when in excess, can actually promote its development and growth. Furthermore, cancer cells can become resistant to inflammatory factors like TNF, and turn things around by using it as fuel to survive and grow. If anything, the relationship is complicated.
NF-κB, MAPKs, and TNF all work together as friends to team up on potential threats. However, as often happens when friends team up, too much of them can be a bad thing – a cellular bully – leading to excess inflammation, damage, and even cancer. Many terpenes and volatile chemicals released by plants appear to reduce all of these cellular pathways, promoting less inflammation, and hopefully less diseases like cancer.
Some data even suggests they may directly provide anti-cancer benefits, but this data is not well-established and is only apparent in preclinical studies (i.e. mostly petri dishes that behave much differently than the human body).13 Regardless, in these experiments, the terpene caused death of the cancer cells by overloading the amount of oxidative stress.14 In other words, much like those good stresses in our life – spices, sulfur-rich veggies, intense exercise, periodic ketosis, and intermittent fasts – the chemicals from plants may be stressing or cells, and helping to fine-tune and exercise their defense mechanisms.
Forest Bathing – Moving Forward
The benefits of forest bathing are plenty. A simple and easily overlooked aspect of our health, physicians may wish to start prescribing it (yes, I do). The benefits are plenty and, unlike most anti-stress medications available, the side effects are minimal (bears aside). For instance, a recent analysis has revealed that nature, a simple and often overlooked part of daily life, provides an important space for refection for cancer patients during their stressful period of treatment.15
In the last article, we talked about the IGF-1, the double-edged sword of heath. However, forest bathing may be the ultimate yin and yang as it provides intense mental stress relief, while potentially stressing our cells at the same time. Either way, the benefits of exposing yourself to some green and forest bathing are obvious.
Finish reading this article and head to your nearest forest!
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Forest Bathing References:
- Ward Thompson, C. et al. More green space is linked to less stress in deprived communities: Evidence from salivary cortisol patterns. Landsc. Urban Plan. 105, 221–229 (2012).
- Takano, T., Nakamura, K. & Watanabe, M. Urban residential environments and senior citizens’ longevity in megacity areas: the importance of walkable green spaces. J. Epidemiol. Community Health 56, 913–8 (2002).
- Grahn, P. & Stigsdotter, U. A. Landscape planning and stress. Urban For. Urban Green. 2, 1–18 (2003).
- Barton, J. & Pretty, J. What is the Best Dose of Nature and Green Exercise for Improving Mental Health? A Multi-Study Analysis. Environ. Sci. Technol. 44, 3947–3955 (2010).
- Park, B. J., Tsunetsugu, Y., Kasetani, T., Kagawa, T. & Miyazaki, Y. The physiological effects of Shinrin-yoku (taking in the forest atmosphere or forest bathing): evidence from field experiments in 24 forests across Japan. Environ. Health Prev. Med. 15, 18–26 (2010).
- Gershenzon, J. & Dudareva, N. The function of terpene natural products in the natural world. Nat. Chem. Biol. 3, 408–414 (2007).
- Phillips & Croteau. Resin-based defenses in conifers. Trends Plant Sci. 4, 184–190 (1999).
- Falk‐Filipsson, A., Löf, A., Hagberg, M., Hjelm, E. W. & Wang, Z. d‐Limonene exposure to humans by inhalation: Uptake, distribution, elimination, and effects on the pulmonary function. J. Toxicol. Environ. Health 38, 77–88 (1993).
- Crowell, P. L. & Gould, M. N. Chemoprevention and therapy of cancer by d-limonene. Crit. Rev. Oncog. 5, 1–22 (1994).
- Crowell, P. L. et al. Chemoprevention of mammary carcinogenesis by hydroxylated derivatives of d-limonene. Carcinogenesis 13, 1261–4 (1992).
- Rufino, A. T. et al. Anti-inflammatory and Chondroprotective Activity of (+)-α-Pinene: Structural and Enantiomeric Selectivity. J. Nat. Prod. 77, 264–269 (2014).
- Ma, J. et al. Linalool inhibits cigarette smoke-induced lung inflammation by inhibiting NF-κB activation. Int. Immunopharmacol. 29, 708–713 (2015).
- Cho, K. S. et al. Terpenes from Forests and Human Health. Toxicol. Res. 33, 97–106 (2017).
- Jin, K.-S. et al. α-pinene triggers oxidative stress and related signaling pathways in A549 and HepG2 cells. Food Sci. Biotechnol. 19, 1325–1332 (2010).
- Blaschke, S. The role of nature in cancer patients’ lives: a systematic review and qualitative meta-synthesis. BMC Cancer 17, 370 (2017).
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