Considering that over a third of the population is expected to get cancer in their lifetime, it would foolish to ignore the potential of our body’s natural ability to reduce cancerous tumors and virally infected cells.
Natural killer cells (NK cells) are an aggressive part of our immune system that plays an important role in removing damaged cells from the body. NK cells are a type of lymphocyte, which in turn are one of the type of white blood cells in the body
These killer cells are cytotoxic – that means that they are bad for a cancer cell, and good for us. Small granules in a killer cell cytoplasm contain proteins called perforin and protease (granzymes) that help to kill unwanted, or diseased cells.
There is now an increasing body of medical and scientific evidence that is suggesting that one of the most powerful healing characteristics of forests has to do with phytoncides, the aromatic essential oils that are emitted from trees in densely wooded areas. Like many other kinds of organic compounds produced by a variety of plants, phytoncides has been shown to have a powerful effect on the immune system.
A number of studies (some of which are listed below) point to the following:
- Phytoncides released from trees (especially isoprene, alpha-pinene, and beta-pinene), that are absent from urban environments, decrease stress hormone levels that may in turn contribute to the increased NK activity.
- The level and activity of NK, granulysin-, perforin-, and granzymes A/B-expressing cells (intracellular anti-cancer proteins) on forest bathing days were significantly higher than in control days.
- The increased NK activity levels were maintain at least 30 days after a day trip to the forest suggesting that a forest bathing trip once a month would enable individuals to maintain a higher level of NK activity.
Further research and robust, peer reviewed clinical evidence needs to take place and more research on the types of other phytoncides (and if these have NK elevating qualities) in our forests but there is no doubt that the existing evidence is pointing in a promising direction.
Li, Q. (2010). Effect of forest bathing trips on human immune function. Environmental Health and Preventative Medicine. 15(1): 9-17. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2793341/.
Li, Q., Kawada, T. (undated but probably 2010). Healthy forest parks make healthy people: Forest environments enhance human immune function. Department of Hygiene and Public Health, Nippon Medical School, Tokyo, Japan. http://www.hphpcentral.com/wp-content/uploads/2010/09/5000-paper-by-Qing-Li2-2.pdf.
Li, Q., Kobayashi, M., Kawada, T. (2008). Relationships Between Percentage of Forest Coverage and Standardized Mortality Ratios (SMR) of Cancers in all Prefectures in Japan. The Open Public Health Journal. 1: 1-7. http://www.benthamscience.com/open/tophj/articles/V001/1TOPHJ.pdf.
Li Q, Kobayashi M, Wakayama Y,Inagaki H, Katsumata M, Hirata Y, Hirata K, Shimizu T, Kawada T, Park BJ, Ohira T, Kagawa T, Miyazaki Y. (2009). Effect of phytoncide from trees on human natural killer cell function. International Journal of Immunopathology and Pharmacology. 22(4):951-959. http://europepmc.org/abstract/MED/20074458/reload=0;jsessionid=BnlPLmTxArJ6VpF0s4MU.6.
Li, Q., Morimoto, K., Nakadai, A., Inagaki, H., Katsumata, M., Shimizu, T., Hirata, Y., Hirata, K., Suzuki, H., Miyazaki, Y., Kagawa, T., Koyama, Y., Ohira, T., Takayama, N., Krensky, A.M., Kawada, T., (2007). Forest bathing enhances human natural killer activity and expression of anti-cancer proteins. International Journal of Immunopathology and Pharmacology. 20(2 Suppl 2):3-8.
Li, Q., Nakadai, A., Matsushima, H., Miyazaki, Y., Krensky, A., Kawada, T., Morimoto, K. (2006) Phytoncides (Wood Essential Oils) Induce Human Natural Killer Cell Activity. Immunopharmacology and Immunotoxicology, 28:319-333. http://www.ncbi.nlm.nih.gov/pubmed/16873099
Angeli A. Circadian rhythms of human NK cell activity. Chronobiologia. 1992;19:195–8.PubMed