I subscribe to a forestry publication called the NCWoodlands Review.

The review is rarely more than four pages long, and it comes out only four times a year, so you have an idea of just how much information is gleaned from reading this paper. The primary purpose of the publication is to keep woodland owners up to date on current state forestry programs and research.

This past month’s edition contained a short article titled “How Forests Boost Immunity.” The essence of the article is that, in addition to lowering blood pressure, pulse rate and levels of the stress hormone cortisol, spending time in nature boosts our immune system too. A study done in Japan took men between the ages of 37 and 55 on a three-day outdoor excursion in the forest. Each day the men walked in the forest for two to four hours. Blood samples taken on day three showed that 92 percent of the men had a 50 percent increase in natural ‘killer’ cells, one of the main components of the immune system that plays a central role in fighting tumors and viruses. Further studies have shown that these positive immune benefits can last up to a month after a visit to the woods.

Researchers believe that the increase in natural killer cells is in part a response to phytoncides, the essential oils in wood that help protect it from insects and rotting. In Japan, where the studies were originally conducted, the practice of getting people out in the woods to promote health has become so popular that the government there is creating official forest therapy sites, and companies are adding forest therapy to their health plans.