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02: Forest Medicine

“Shinrin-yoku” or forest bathing is not new to Japanese people. Indeed, Japanese people have been enjoying a short walk in a forest for centuries. This does not come as a surprise. Among developed countries, Japan's rate of forest land is second to Finland, and thus Japan can be said to be one of the most heavily forested countries in the world. For reference, the world's rate of forest land is approximately 30% whereas the total land of forest accounts for 67% of the land in Japan. Given the rate of forest land in other countries; such as, U.S., Germany, and Switzerland, that only amount to 30% respectively, we could say forest walking is a pastime meant for Japanese people.

Recently this “Shinrin-yoku” has come to our attention in the medical field as well. “Forest Medicine is a new branch of study in the field of public health. It is recognized as new research area within the environmental immunology, and in fact, Nippon Medical School has taken up a lot of shares in establishing this field of study,” says Dr. Qing Li, an Associate Professor at the Department of Hygiene and Public Health of Nippon Medical School. Dr. Li is also a main member of “The Task Force of Forests and Human Health” within International Union of Forest Research Organization. He is also a founding member and current President of “The Society for Forest Medicine” within the Japanese Society for Hygiene.

Since 2005, his research team has been working on field studies on forest medicine, and has introduced a multiple epic results in this field. For example, one research conducted in 2005 showed the effects of forest bathing trips on human immune function. “To clarify the medical effect of forest bathing, we investigated mainly natural killer (NK) activity, number of NK cells, and anti-cancer enzyme expression in peripheral blood lymphocytes, during our visit to forest fields,” says Dr. Li. Earlier results have shown that higher NK activities of healthy individuals have positive correlation with not developing cancer.

For this experiment, twelve Japanese adult male experienced a 3-day/2-night trip to forest parks. Blood as well as urine samples were measured for Natural killer (NK) activity, the numbers of NK cells, granulysin-, perforin-, and granzymes A/B-expression on days 2 (the first sampling during each trip) and 3 (the second sampling during each trip), and on days 7 and 30 after the trips. The same measurements were made before the trips on a normal working day as a control.

The results showed that NK activity and the numbers of NK cells, as well as the number of granulysin-, perforin-, and granzymes A/B-expressing cells were significantly higher in the forest bathing samples, compared to normal working day samples. In addition, increased NK activity lasted for more than 30 days after the trip, suggesting that merely a once a month forest bathing trip would enable individuals to maintain a higher level of NK activity (Figure 1 to 4). “These findings indicate that forest bathing could build bodies that may be resistant to cancer development,” says Dr. Li. “We will continue with the research and will continue to popularize the concept of forest medicine around the world.”

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