Bored at home? Don’t know what to do? Then we suggest you go take a walk through an area with a lot of trees and preferably as much nature as possible. Why? Walks have a multitude of obvious benefits like getting fresh air and oxygen into your system, circulating blood and moving your muscles, and it’s great for your mental health since it provides you time away from work to think, relax, or just walk. However, there is an enormous benefit to your immune system as well when walking in forested and natural areas.
Multiple studies have shown that the act of walking in a forest can significantly boost natural killer cell activity in your body. Natural killer (NK) cells are lymphocytes that are in the same family as our body’s T and B cells (part of our immune system. NK cells are known for their ability at killing virally infected cells and detecting and controlling early signs of cancer. They are also found in the placenta and may play an important role in pregnancy.
A study published in 2007 by Japanese scientists had 12 subjects from Tokyo visit and walk in different forest fields over a two day period. Blood analysis was taken throughout and NK activity was measured through proportions of NK, T cells, granulysin, perforin, and granzymes A/B expressing cells. 11/12 subjects showed significantly higher levels of NK activity post forest walks (about 50% increased).
A version of this study was also done with female subjects and this time, blood was tested 7 and 30 days after the forest walks. Thirteen healthy nurses were selected, aged 25-43 years old. They walked in forest fields on day 1 and 2, and then returned to the city on day 3. Blood analysis measuring NK activity was performed and showed that the significant increase in NK activity lasted 7 days after the trip, with increased activity still present on day 30.
Taking walks in forested areas has a proven effect on raising the power of our immune system and this may partially be attributed to phytoncides released by plants in forested areas and the decreased stress levels from the act of going on a walk. Phytoncides are volatile organic compounds that are released by plants to protect themselves from insects, animals, disease, and rot. When we walk in a forest or in nature, we are breathing in a lot of these phytoncides, which have a positive effect on our immune system.
The effects of phytoncides have been shown in another study by the Japanese team that did the forest walking studies. In this study, the team had 12 healthy males stay in a hotel room for three nights from 7pm to 8am. During their stay, the scientists vaporized essential oils derived from trees (they used hinoki cypress) with a humidifier to release phytoncides into the room. Phytoncide concentration in the room was measured along with blood and urine samples from the subjects. Phytoncides like alpha-pinene and beta-pinene were detected in the room, along with significantly increased NK cell activity in the subjects.
The positive effects of walking in a forest for humans has been so recognized by the Japanese Ministry of Agriculture, Forestry, and Fisheries that they coined an official term for walking in a forest in 1982: shinrin-yoku. This translates as “forest bathing” and they encourage citizens to regularly immerse themselves in forests and to go on walks.
All of these studies tells us that:
Walking in forested areas will increase natural killer cell activity
At a minimum, we should take walks in forests once every 7 days to maintain a significant increase in NK activity, although increased activity may be present for up to 30 days post walk.
If you can’t find a forest or have to stay at home, vaporizing essential oils derived from woods could reproduce similar effects
More studies need to be done in North America. We share some of the same genera of trees with Japan like pine, oak, and birch but we have different species