Why your immune system needs a forest
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For millions of years, the immune system of our ancestors coevolved with its environment. There are gazillions of viruses, bacteria and other microorganisms out and about to which living beings are being exposed to on a daily basis. Some are beneficial and some harmful, so life learned to collaborate with the benign ones (there are more non-human cells in your body than human cells) and to defend itself to the harmful ones (the immune system of healthy living organisms is still the most sophisticated security system in the world). Because of the process of coevolution, life learned to immunize itself to infectious diseases and the immune system of the forest dwellers evolved in concert with the immune system of the forest.
Picture by Raf Gorissen
Even though we have reduced most of the forests of the world to charcoal, toilet paper, building material and dust, the remaining forests still offer us an incredible immune boost. Nearly 1,000 scientific studies “point in one direction: Nature is not only nice to have, but it’s a have-to-have for physical health and cognitive function,” according to the Yale School of Forestry & Environmental Studies.
For instance, studies with students and elderly show that spending time in nature significantly reduces inflammation. Additionally, research from the Nippon Medical School in Japan shows that time spent in forests increases the number of natural killer cells, which promote our immune defense, while expanding the functional activity of these antiviral cells. What is more, the research also showed that forest visits increase the amount of intracellular anticancer proteins and this effect lasted for a full week after the trip. None of these effects were observed after city trips.
Other studies show that natural aromas secreted by evergreen trees, known as phytoncide, are associated with improvements in the activity of human frontline immune defenders. Nature’s health benefits are thus wide-ranging and strong associations between access to nature and longer, healthier lives are increasingly revealed by science. A study in Environmental Health Perspectives of 2016 for example, found a 12% lower mortality rate in people that live in close proximity to nature, even after correcting for socio-demographic background and smoking habits, with the biggest improvements related to reduced risk of death from cancer, lung disease or kidney disease.
So, your immune system needs a forest. A healthy wild forest, not a sterile park or plantation. These times of lock-down due to the COVID-19 outbreak where many activities get canceled, are the perfect time to reflect on what we can do to improve our immune system. Every city its own urban forest would be a great start. Because nature is better for our health than the health care system.
Here are some references on the interdependence of nature and health:
Yale School of Forestry & Environmental Studies: Robbins J. 2020. “Ecopsychology: How Immersion in Nature Benefits Your Health”, YaleEnvironment360. https://e360.yale.edu/features/ecopsychology-how-immersion-in-nature-benefits-your-health
Selhub EM & Logan AC. 2012. Your brain on nature. John Wiley & Sons.
Li Q. 2010. Effect of forest bathing trips on human immune function.
Environ Health Prev Med 15(1): 9–17.
Li Q 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(1):45-55.
Preuß M et al. 2019. Low Childhood Nature Exposure is Associated with Worse Mental Health in Adulthood. International Journal of Environmental and Public Health 16(10): 1809. https://doi.org/10.3390/ijerph16101809
Mao GX et al. 2012. Effects of short-term forest bathing on human health in a broad-leaved evergreen forest in Zhejiang Province, China. Biomed Environ Sci 25(3):317-24. doi: 10.3967/0895-3988.2012.03.010.
Gorissen L. 2020. Building the Future of Innovation on millions of years of Natural Intelligence. Wordzworth.