What if your psychiatrist prescribed a trip in the forest vs antidepressants?
As a common practice in Japan, “Shinrin-yoku” are short visits to forests that allow to breath in volatile substances which improve overall immune function. A walk or trip in the forest corresponds to natural aromatherapy practice, and evidences have shown that significantly decreases anxiety, depression and anger.
Because of the presence of scents, especially those emanated by conifers (phytoncides), which are commonly known as “wood essential oils”, the risk of psychosocial stress-related disease was found to be lower in individuals who take habitual forest bathing as part of their lifestyle. (1,2)
Resins produced by plants in forests are mainly composed by lipid molecules, terpenes, which play a prominent role in traditional herbal remedies (as well as in a variety of other purposes, from cooking flavors to cleaning product scents).
There is an incredible variety of terpenes in nature, a number well over 10,000, varying in structure, scent and function, and are of immense importance to us.
Some examples comprise of humulone, constituent of hops, which you may are familiar with, if you like the bitter flavor of your beer; Menthol, is probably part of your toothpaste and lemongrass of the washing liquid, geraniol of your anti-mosquito stick, and lavander of your evening herbal tea..
Some terpenes show anti-depressant and calming, anxyolitic effects.
Clearly, unless for specific allergies, the terpenes studied are safe substances used in almost all facets of human endeavors, yet their role is not taken much in consideration by most psychiatrists & psychologists. (3)
Moreover, these substances show great bioavailability, meaning that positive effects can take place even at undetectable concentration in the serum, and can be absorbed easily by pulmonary intake as well as ingestion and skin absorption. (4,5)
What terpenes can play antidepressant- anxiolytic role?
Limonene 
Several behavioral studies were performed in rodents dosed with citrus oils showing consistently that limonene reduced significantly anxiety & social stress. (6; 7)
Limonene was demonstrated to mediate its antidepressive effects via the receptors 5-HT 1A, which increase serotonin (a neurotransmitter that regulates mood) in the prefrontal cortex; This brain region is associated with personality expression, decision making and social interactions.
Moreover, limonene increases dopamine (a neurotransmitter that contributes to feeling of reward) in the hippocampus (the brain area that controls learning & memory). (8, 9).
These effects have been confirmed by a clinical study with hospitalized depressed patients exposed to citrus fragrance in ambient air, with subsequent normalization of Hamilton Rating Scale for Depression, successful discontinuation of antidepressant medication in 9/12 patients and amelioration of immune response. (Inflammation contributes enormously to depressive states, check here) (10)
D-Linalool
Is a terpene with well-established anxiolytic activity. It is psychotropic, and plays a crucial role in the sedative and calming effects of Lavander as well as Cannabis.
Linalool acts via GABA modulation, making this essential oil important in the treatment of seizures, stress & anxiety. (GABA is in fact the main inhibitory neurotransmitter & is targeted by anxyolitics & anticonvulsants).
Lavander oil may also aid sedating obsessive behaviors of addicts (such as compulsive shopping, eating and drug taking), as demonstrated by a clinical study with obese patients undergoing gastric bypass, reducing their need for administration of morphine following the intervention vs those who did not take lavander oil. (12)
Phytol
Phytol, present in most green plants, increases GABA by blocking one of its degrading enzymes which could account for relaxing effects of Cannabis Sativa & Lactuca Sativa.
Effects of “Forest bathing trips” on stress hormones
The measurements of free adrenaline and noradrenaline in urine provides a reliable measure of the circulating concentration of these hormones in the bloodstream. Lower stress is associated with decreased concentration of sympathoadrenal activity.
Likewise, subjects who undertake the several clinical trials run in Japan on “forest bathing trips” were found consistently to show a significant decrease of urine adrenaline and noradrenaline concentration; This event was equally evaluated in female as well as in male subjects. (1)
Follow-ups studies were undertaken in 2008 in order to understand whether lower stress was exclusively due the fact that examined subjects were having time off work, so another clinical trial took place. This time the subjects were prompted to walk leisurely (as they were during the forest bathing trips) visiting a city without the presence of forests or conifers-parks.
The city tourist visit had no effect on stress hormones levels, suggesting once again that the natural setting was indeed key to achieve the positive results, as shown in the figure below.
Lower levels of circulating Adrenaline were also associated with direct increase in human natural killer activity (NK), with a prominent role in anti-cancer activity, as we will see in a future article on terpenes and cancer prevention. (13, 14)
Moreover, another indicator of depressive states is found in circulating levels of cortisol, as we discussed in depth in this video. Forest bathing trips showed to reduce saliva cortisol levels, as well as stabilise autonomic nervous activity. (15, 16)
How often should you do it?
The increased immunologic activity, as well as the lower stress response lasted for more than 30 days after the trip, suggesting that a forest bathing trip a month would be ideal as part of a prevention program; essential oils may be inhaled or massaged on the body of a patient suffering from acute stress or insomnia and the effects tend to be almost immediate, making this method, possibly in conjunction with other lifestyle changes (if you are interested in nutraceuticals that are ideal for management of depression we recommend to check here), a great first-line treatment that is totally devoid of side effects, at contrary with majority of pharmacological intervention (SSRI, MAOs, Benzodiazepines).
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References
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2) Morita, E Fukuda, S Nagano, J Hamajima, N Yamamoto, H Iwai, Y, et al.. (2007). Psychological effects of forest environments on healthy adults: Shinrin-yoku (forest-air bathing, walking) as a possible method for stress reduction. Public Health. 121 (1), 152-9.
3) Simonsen, J L (1947) The Terpenes. Volume I (2nd edition), Cambridge University Press, 230-249
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10) Komori T, Fujiwara R, Tanida M, Nomura J, Yokoyama MM (1995). Effects of citrus fragrance on immune function and depressive states. Neuroimmunomodulation 2: 174–180.
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13) Li Q, Morimoto K, Kobayashi M, Inagaki H, Katsumata M, Hirata Y, et al. (2008) Visiting a forest, but not a city, increases human natural killer activity and expression of anti-cancer proteins. Int J Immunopathol Pharmacol. 21:117-28
14) Li Q, Morimoto K, Kobayashi M, Inagaki H, Katsumata M, Hirata Y, et al. (2008) A forest bathing trip increases human natural killer activity and expression of anti-cancer proteins in female subjects. J Biol Regul Homeost Agents. 22:45-55
15) Park BJ, Tsunetsugu Y, Kasetani T, Hirano H, Kagawa T, Sato M, et al. (2007) Physiological effects of Shinrin-yoku (taking in the atmosphere of the forest)- using salivary cortisol and cerebral activity as indicators. J Physiol Anthropol. 2007;26:123-8
16) Tsunetsugu Y, Park BJ, Ishii H, Hirano H, Kagaw T, Miyazaki Y. (2007) Physiological effects of Shinrin-yoku (taking in the atmosphere of the forest) in an old-growth broadleaf forest in Yamagata Prefecture, Japan. J Physiol Anthrpol. 26:135-42
