It is probably not necessary to mention how incredibly essential the human immune system is to our lives. Without our immune system, we would die from the smallest illness, infection or flu. Our immune system is an incredibly fast and adaptive network in our body and (hopefully) always at our service when bacteria, viruses and fungi threaten us.
This post is about the view, now supported by many studies, that nature can help our immune system become stronger in a number of ways.
However, we are not talking about medicinal plants or herbs here. Rather, it's about us as people in nature and the time we spend in forests, for example, and what influence this has on our health.
The human immune system
But to refresh our knowledge a bit, let's start by briefly looking at the structure and functionality of the immune system.
Our defense system in the body consists of a variety of components so that we are best equipped to deal with an ever-changing environment and all the living creatures, bacteria, viruses or allergens that exist in it. Mechanical barriers stop germs from entering the body at all, these are for example the skin, the intestinal wall or mucous membranes. The cells of our immune system actively fight pathogens and unwanted substances. They produce important proteins, antibodies, to recognize pathogens and messenger substances to alert the rest of the body to invaders. These messengers thus trigger, among other things, inflammation, which is useful up to a point, but harmful in excess.
Part of our immune system is non-specific; it sounds the alarm as soon as invaders are present and, in the best case, fights them successfully. Unlike the specific or acquired immune system, we have had our non-specific immune system since birth. That is why it is also called the innate immune system. (1)
With killer cells against viruses and cancer
This innate IS also includes the white NK cells, the abbreviation standing for "natural killer cells". What sounds like it came out of a Hollywood science fiction movie is actually the first phase of the immune response and especially important for fighting viruses. NK cells can recognize cells that have been infected by a virus and then destroy them. This is important because viruses make themselves at home in cells in our body and use them as a factory, so to speak, to make copies of themselves and multiply. (2)
The NK cells then release substances into the target cell that dissolve it from the inside (perforin, granzyme B). They also produce messenger substances that, as we already know, activate other components in the immune system.
When people are deficient in NK cells, they often suffer from particularly severe and recurrent infections. (3)
However, these NK cells have another, extraordinarily important task. They are involved in the elimination of tumor cells and have the role of "immune surveillance" of cancer in humans. Again, it has been shown that low activity of NK cells is associated with higher risk of cancer and, on the other hand, high activity of NK cells is associated with lower risk. When there are many NK cells in tumor tissue, this is linked to a positive outcome of the disease and is also associated with better response to cancer drug therapy.
It was concluded that functional NK cells are important for fighting tumors and viral infections. Stress, obesity, smoking, alcohol consumption and lack of sleep reduce the content or functionality of NK cells, but other practices can restore healthy levels, including adequate sleep, exercise and forest bathing. (4)
Forest bathing and NK cells
The Japanese Qing Li, from the Department of Hygiene and Public Health at the Nippon Medical School in Tokyo, was one of the first scientists to research the relationship between the forest and the human immune system. Within a few years, he conducted a large number of experiments to show the effect of forest bathing on the immune system.
The practice of forest bathing was able to increase the activity of natural killer cells (NK) in both men and women. Also the substances in the killer cells (perforin, GRN granzyme A and B) which are necessary to destroy affected cells increased in content. However, a similar program in the city did not lead to these positive effects. The effect can last at least 7 days, in some participants even much longer. (5)
The effect could again be triggered by the terpenes we are already familiar with. Cell experiments showed that terpenes increase the activity of NK cells and the content of the substances they contain in a dose-dependent manner. Thus, healthy concentrations of NK cells could be restored in damaged tissues. (6)
A few other research groups and metastudies also looked at NK cells and forest bathing and found that forest bathing can probably increase NK activity and increase the levels of relevant substances in them, although more studies are desired. (7)
An interesting study in Hungary found that the activation of NK cells by forest bathing is detectable in May, but not in January, i.e. in winter. The study also showed that mainly the young, not yet fully matured NK cells are influenced and possibly longer or more frequent excursions would be necessary to activate mature cells. (8)
Oxidative stress and its effect on us humans
Our body is constantly exposed to the danger of oxygen. Yes, you read correctly, oxygen is not only the elixir of life for us humans, it can even cause damage to our body in various processes.
Oxygen itself and its reactive derivatives attack molecules in our bodies and can impair or even damage them. This is called oxidative stress.
There are various ways in which harmful derivatives of oxygen, such as the superoxide radical, can be formed. For example, UV radiation or self-oxidation of unstable intermediates in the body.
Especially during the energy supply in the mitochondria, the fuel cells of our body, many radicals are produced from which we need to protect ourselves. But why? What is the problem with oxidative stress? (9)
Among other things, these reactive molecules can attack our genetic material and cause mutations and DNA breaks there. For example, enzymes, transport proteins or even the membranes of our cells can be damaged. This can possibly show up in oxidized LDL, which is known for its role in the development of vascular calcification.
Okay, we know it's a problem. Our body knows that too and has therefore developed some protective mechanisms for us.
These include the following enzymes and catalysts with sometimes unpronounceable names such as glutathione S-transferase, glutathione peroxidase, superoxide dismutase and catalase.
In addition, there are some molecules, some of which we know all too well, such as vitamin C, vitamin E and other substances that helpfully counteract oxidative processes. Our body is constantly busy repairing damage already done and trying to maintain our antioxidant system.
The studies on our antioxidant system and the effect of forest bathing are manageable, but consistently positive. It must also be admitted here that the effect of trees and nature on the human organism is not as easily measurable as that of vitamin C, for example.
One study shows that forest bathing generally increases antioxidant potential. Another, for example, shows only a specific antioxidant protective effect, through the increase of glutathione peroxidase by forest bathing.
A scientific paper provides evidence of a reduced concentration of the reactive oxygen form H2O2 (hydrogen peroxide).
Two studies showed a completely different form of effect, namely via the reduction of biochemical degradation products during the metabolism of fatty acids (malondialdehyde). (10)
Skin and allergy
With weak certainty, forest bathing could also help with dermatitis, an inflammatory skin disease. This has been studied especially in children, and positive effects have been shown in relation to hypersensitive and allergic skin. One speaks here of the biodiversity hypothesis, that the biodiversity of the substances in the forest could support the immune system. (11)
Interestingly, positive effects are already seen during childhood or pregnancy. They are probably also more effective in influencing the immune system than at a later age. (12)
Recovery in hospital
A particularly well-known, but already older study has shown that the view from the hospital window can have a significant influence on recovery. Patients with a view of trees were discharged from the hospital earlier, were more likely to use weak rather than strong medications, and were less likely to be perceived by nurses as having negative moods and health conditions. Patients were compared who had the same surgery but only had a view of a stone wall from their room. This shows us that not only the forest substances, but also the sight and psychological factors of the forest and nature have an effect on our physical health. (13)
If you are particularly interested in this effect, then I recommend the already published article on the subject of forest bathing under the title: "How the forest heals us and keeps us healthy! Blog or Podcast!
Corona Pandemic (Covid 19) and the effect of nature
With the outbreak of the Covid pandemic, research groups also looked at forest bathing and viral diseases. In regions of Italy, they found a correlation between the severity of the pandemic and environmental factors such as air pollution, the scarcity of deciduous trees, and a Mediterranean diet. Such studies are still sporadic and provide only limited scientific certainty, but show us that forest bathing and nature seem to be gaining acceptance in current research and can also be taken seriously as a medically useful application. (14)
My conclusion on the effect of forest bathing on our immune system
I think the scientific evidence is very promising. Our health and immune system can benefit greatly from spending time in the forest. Nature in general is a source of energy and well-being for humans. The future will prove this in further studies. But you can already feel the difference in yourself and use the decelerating effect of the forest. Go more into the forest in intense and stressful times, or in times of illness and bathe yourself in it and its atmosphere. Your mood and well-being will rise and your immune system will get support.
As I have shown in previous articles, spending time in a forest has a strong advantage over a park or garden. What kind of forest, what kind of tree and at what time of year the stay there is to be considered ideal, we can decipher from the current data.
There is some evidence to suggest that spring and summer are the more effective times, simply because of the flowering and the significantly higher levels of messenger substances in the forest. As in the study from Hungary, around the natural killer cells, May is shown to be particularly effective.
But despite all the uncertainties, it must be said that the forest has an effect at any time of year. Be it the decelerating and stress-regulating effect or the general health-promoting effects through exercise and fresh air.
Eight different articles and podcasts have appeared on the topic of forest bathing. Here you can find them listed and switch between them in the order of your choice.
Blog article:
- Forest bathing (Shinrin Yoku) for body, mind and soul
- How forest bathing affects our psyche & mental health
- Lower stress levels with forest bathing
- Smarter through forest bathing? How does our brain benefit from nature?
- How the forest heals us and keeps us healthy!
Podcasts (on Youtube):
- Forest bathing (Shinrin Yoku) for body, mind and soul
- How forest bathing affects our psyche & mental health
- Lower stress levels with forest bathing
- Smarter through forest bathing? How does our brain benefit from nature?
- How the forest heals us and keeps us healthy!
You can find these podcasts under the same titles on all popular podcast platforms (e.g. Spotify, Apple Podcast, etc.).
I send you energetic greetings
Your optimizer
Richard Staudner
PS → On Instagram I provide you with exciting biohacks about health, longevity and performance! Visit me there under richard_staudner
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(1-4) Löffler, 2007 Deng et al., 2021
(5-6) Li, 2010
(7) Andersen et al, 2021; Antonelli et al, 2021; Rajoo et al, 2020; Stier-Jarmer et al, 2021.
(9) Löffler, 2007
(10) Hansen et al., 2017; Wen et al., 2019.
(11-12) Antonelli et al, 2021; Stier-Jarmer et al.
(13) Ulrich, 1984
