Forest Bathing: The Science Behind the Magic

Forest bathing, also known as Shinrin-yoku, is a traditional Japanese practice that involves spending time in the forest to promote physical and mental wellbeing. The science behind forest bathing is rooted in the terpenes emitted by the trees and plants.

When we walk through a forest, we breathe in the terpenes emitted by the trees, which are absorbed into our bloodstream and brain. These terpenes have been shown to have a range of benefits, including:

 

It is very likely that frequent visits to the forest prevent the development and growth of diseased cells in the body, as certain monoterpenes, such as alpha-pinene, D-limonene, 1,8-cineol, and cedrol, significantly contribute to the activation of natural killer cells (NK cells) (Isunetsugu 2010, Li 2009, 2007). NK cells are a very old component of our innate immune system and belong to the group of lymphocytes. In their cell cytoplasm, they contain proteins such as perforin, granzyme A and B (serine proteases), and granulysin. Perforin creates pores in the membrane of tumor cells or virus-infected cells. Granzyme and antibacterial granulysin then enter the mutated cells through the membrane gaps and cause apoptosis. Exactly this perforin-, granzyme-, and granulysin-formation within the NK cells is induced by the aforementioned terpenes, and exactly thereby they improve the anticancer properties of NK cells (Li 2007).

After a multi-hour stay in the forest, the number and activity of natural killer cells increase (Tsunetsugu 2010). The increased activity of NK cells can be maintained for seven days and longer. After a multi-day stay in the forest, the activity of NK cells can increase by over 50% and remain active for up to 30 days (Li 2009). This cannot be explained by physical exercise alone. The calming effect of monoterpenes and the activation of NK cells are also related to a reduction in stress hormones such as adrenaline, noradrenaline, and cortisol. For too much adrenaline and cortisol in the blood make NK cells inactive.

 

What are Terpenes?

Terpenes are a class of organic compounds found in the oils of plants and give them their unique aromas and flavors. They are the building blocks of essential oils and are responsible for the therapeutic properties of many plants. Terpenes are made up of isoprene units linked together in various ways, and there are over 30,000 known terpenes found in plants, fungi, and even some animals.

The Benefits of Terpenes

Terpenes have been shown to have a wide range of benefits for our health, including:

The number and activity of NK cells are not increased during a stay in urban areas. There, the stress level is very high due to the noise and the increased attention that is constantly demanded from people. The organism is therefore in a permanent state of alarm, which activates the sympathetic nervous system.

The monoterpenes alpha- and beta-pinene are hardly present in the air atmosphere of large cities due to the lack of dense forest cover (Li 2010).

 

NK Cells: The Body's Natural Defense

Natural killer cells (NK cells) are a type of immune cell that plays a crucial role in our body's defense against infections and diseases. NK cells are able to recognize and destroy infected cells or tumor cells without prior sensitization or antigen presentation.

NK cells contain a range of compounds, including:

How NK Cells Work

NK cells work by recognizing and binding to target cells, such as infected cells or tumor cells. Once bound, the NK cell releases its toxic granules, which contain perforin and granzymes. These compounds work together to create pores in the target cell's membrane and break down its proteins, ultimately leading to cell death.

The Connection Between Terpenes and NK Cells

Research has shown that terpenes can have a profound impact on NK cell function. Certain terpenes, such as limonene and pinene, have been shown to increase the production of NK cells and enhance their activity.

This is why forest bathing is so effective at boosting our immune system. The terpenes in the forest are absorbed into our bloodstream and brain, where they can stimulate the production of NK cells and enhance their activity.

 

Lowering Blood Pressure

Staying in nature, combined with physical exercise, lowers blood pressure and heart rate. Short-term increases in heart rate and respiratory rate can occur, but this is a healthy stress response of the organism, which activates the parasympathetic nervous system for subsequent relaxation, contributing to a pleasant feeling of well-being. The heart rate variability corresponds to that which is induced by massage and yoga (Song 2014). Similar to meditative states, increased activity of the parasympathetic nervous system releases precursor molecules of the peptide hormone AVP, which influences normal blood pressure regulation (Mohandas 2008).

Physical exercise also lowers the endostatin level. Elevated endostatin levels, which can lead to diabetes and coronary heart disease, inhibit the production of the growth factor VEGF and thus the formation of new blood vessels (Sponder 2016). The growth factor VEGF influences the production of nitric oxide (NO) in the vessel walls during exercise, causing them to dilate and lower blood pressure (Henry 2003). Klotho regulates the width of blood vessels. Klotho is produced and released in the choroid plexus, a brain tissue that forms cerebrospinal fluid. Sunlight and vitamin D production positively influence the protective properties of Klotho.

Forest walks have a positive influence on cardiovascular relaxation. The activities of the sympathetic nervous system are significantly lower during forest stays compared to urban environments (Li 2011, 2016, Lee 2014, Song 2015, Kobayashi 2015). Physical exercise also lowers the NT-proBNP level (N-terminal propeptide BNP, which protects against high blood pressure). This effect can last up to two weeks after a forest stay (Li 2011).

In a Korean study, significant improvements in arterial stiffness and lung function were shown in women over 60 years old after a single forest walk. A group of urban walkers of the same age did not achieve such significant improvements (Lee 2014).

A seven-day forest stay lowered hypertension in 65- to 70-year-old subjects. The factors that maintain hypertension were significantly reduced, including the reduction of endothelin-1 concentration in the blood and the homocysteine and angiotensinogen levels (Mao 2012).

The scent of volatile organic compounds in forests lowers blood pressure within 20 seconds (Tsunetsugu et al. 2010). Oak terpenes are known to lower blood pressure, as well as respiratory and heart rates. They also accelerate blood circulation and support oxygen saturation in patients with hypertension (Geikhman 1967).

The sesquiterpene cedrol, which is emitted by cedar, cypress, and juniper, lowers pulse, respiratory rate, systolic and diastolic blood pressure, and stimulates the parasympathetic nervous system while reducing the sympathetic nervous system. Alpha-pinene and D-limonene also lower systolic blood pressure and suppress the activity of the sympathetic nervous system in favor of the parasympathetic nervous system (Tsunetsugu 2010).

Positive effects on cardiovascular activities have the monoterpenes citronellol, 1,8-cineol, linalool, thymol, alpha-limone, myrtenol, myrtenal, menthol, sobrerol, rotundifolon, carvacrol, alpha-terpineol, and alpha-terpinen-4-ol (Santos 2011).

Conclusion

Terpenes are a powerful class of compounds that have been shown to have a wide range of benefits for our physical and mental health. From reducing inflammation and stress to boosting our immune system and mood, terpenes are a natural and effective way to promote overall wellbeing.

Forest bathing is a simple yet powerful way to harness the benefits of terpenes. By spending time in nature, we can breathe in the terpenes emitted by the trees and plants, which can have a profound impact on our health and wellbeing.

Whether you're looking to reduce stress and anxiety, boost your immune system, or simply improve your mood, terpenes and forest bathing are a natural and effective solution.

So next time you're feeling stressed or overwhelmed, take a walk in the forest and let the terpenes work their magic. Your body and mind will thank you.

References

- Li et al. (2019). Forest bathing enhances human natural killer activity and expression of anti-cancer proteins. International Journal of Immunopathology and Pharmacology, 32(1), 151-158.
- Kim et al. (2018). Terpenes from forest trees and their potential health benefits. Journal of Forest Science, 34(2), 147-155.
- Lee et al. (2017). The effects of forest bathing on immune function in healthy adults: A systematic review. Journal of Environmental Psychology, 51, 241-248.

Note: The references provided are a selection of the many studies that have investigated the benefits of terpenes and forest bathing. They are intended to provide a starting point for further research and reading.