The test subjects were divided into two groups: those who stayed in an urban environment and those sent to a forested area. Both groups engaged in the same activities and ate the same diet. It is thought that the chemical phytoncides, an oil that defends trees from insects and decomposition, somehow affect the chemicals in the human brain.
In other studies, it was demonstrated that there was an increase in natural killer cells that fight cancer, an increase in white blood cells, and a reduction of glucose levels in diabetics.
In the U.K. and in Europe, depression is being treated with farm work and gardening. Whether it is tending plants or animals, the act of caring for something alive in the fresh air has had a positive effect on patients with clinical depression.