Nature not only reduces symptoms of low grade chronic stress, but also stimulates the immune system.
I am more likely to remain healthy and strong the more time I spend in nature. And there is science to back this up.
A key player in the human immune system is the Natural Killer (NK) cell, a type of white blood cell (lymphocyte) that specializes in the elimination of cancer cells and ones infected with viruses. They do this by releasing proteins (perforin, GRN and GRA/B) that hunt down and destroy a targeted cell.
To test for immune system activity, scientists draw blood, count the NK cells present and test for intercellular concentrations of these proteins — thus determining the activity and robustness of the immune system.
In early September 2005, Juyoung Lee, Qing Li, and Yoshifumi Miyazaki from Japan's Chiba University and Nippon Medical School took a group of 12 people and tested their blood for NK activity in the urban setting. This was their "control". Then they went on a three day/two night trip to a forest area in northwest Japan. After the second day of hiking they took blood samples which they analyzed for NK activity and presence of the above mentioned proteins.
They found that the subject's NK activity had increased by 56%.
Not only that, but a month later, their NK activity was elevated 23%.
A separate study found that even short trips, a 30 minute walk in a city park, positively effect NK activity which remains significant seven days later. LINK