Ways to boost your immune system

Boosting your immune system is a great strategy in general, but especially during a pandemic. I have been researching a lot about real options to properly activate the immune system, in a way that does not over-activate it, hint to all my allergic pals suffering the spring haze fever!
In this quest for healthy protocols, I found forest bathing. Back in 2007, a group of American and Japanese scientists studied the effect of forest bathing on the human immune system. Particularly they measured some cells involved in the protection of the body, such as natural killers (NK); measuring the number of NK cells, and perforin, granzymes and granulysin-expression in peripheral blood lymphocytes (PBL) during a visit to forest fields. The study involved 12 healthy male adults who experienced a three-day/two-night trip and walks in three different forest fields. As a control, they took the same measurements on a working day without visiting any forest. Almost all the subjects (11/12) showed higher NK activity after the trip (about 50% increased) compared with before. The forest bathing significantly increased the numbers of NK, perforin, granulysin, and granzymes AlB-expressing cells. They concluded that their findings indicate that a forest bathing trip can increase NK activity and that this effect is at least partially mediated by increasing the number of NK cells and by the induction of intracellular anti-cancer proteins.
Moreover, they followed up with an investigation of how long the increased NK activity lasts and compared the effect of a forest bathing trip on NK activity with a trip to places in a city without forests. Blood and urine were sampled from the 12 subjects that participate in the study and also phytoncide concentrations in forest and city air were measured. They reported that: “the forest bathing trip significantly increased NK activity and the numbers of NK, perforin, granulysin, and granzyme AlB-expressing cells and significantly decreased the concentration of adrenaline in the urine. The increased NK activity lasted for more than 7 days after the trip. In contrast, a city tourist visit did not increase NK activity, numbers of NK cells, nor the expression of selected intracellular anti-cancer proteins, and did not decrease the concentration of adrenaline in the urine. Phytoncides, such as alpha-pinene and beta-pinene were detected in the forest air, but almost not in the city air. These findings indicate that a forest bathing trip increased NK activity, the number of NK cells, and levels of intracellular anti-cancer proteins, and that this effect lasted at least 7~ays after the trip. Phytoncides released from trees and decreased stress hormone may partially contribute to the increased NK activity.”
In 2009 they investigated the effect of essential oils from trees on human immune function in twelve healthy male subjects, who stayed at an urban hotel for 3 nights. Aromatic volatile substances (phytoncides) were produced by vaporizing Chamaecyparis obtusa (hinoki cypress) stem oil with a humidifier in the hotel room during the night stay. Blood samples were taken on the last day and urine samples were analysed every day during the stay. NK activity, the percentages of NK and T cells, and granulysin, perforin, granzyme AlB-expressing lymphocytes in blood, and the concentrations of adrenaline and noradrenaline in urine were measured. Similar control measurements were made before the stay on a normal working day. The concentrations of phytoncides in the hotel room air were measured. Phytoncide exposure significantly increased NK activity and the percentages of NK, perforin, granulysin, and granzyme AlB-expressing cells, and significantly decreased the percentage of T cells, and the concentrations of adrenaline and noradrenaline in urine. Phytoncides, such as a-pinene and ~-pinene, were detected in the hotel room air. These findings indicated that phytoncide exposure and decreased stress hormone levels may partially contribute to increased NK activity.
These results are very encouraging, but the reduced number of participants puts a question mark on the results. Fortunately, there are no known adverse events (besides the allergies that I mentioned before) for a nice stroll in a park or forest, so why not just go for a walk and take a deep breath hoping that will boost our immune system, or at least that the placebo effect will do the job!

References:

https://journals.sagepub.com/doi/pdf/10.1177/03946320070200S202

https://journals.sagepub.com/doi/pdf/10.1177/039463200802100113

https://journals.sagepub.com/doi/pdf/10.1177/039463200902200410

Bluebells in London