"Researchers at the Nippon Medical School took twelve healthy men, from thirty-five to fifty-six years of age, out of Tokyo and into the forest. For three days they followed a regimen: the first day they walked among the trees for two hours, the second day for four hours, and on day three they offered blood and urine samples and filled out a questionnaire. They were sampled a week and a month after the trips as well, and these results were compared to samples taken after walks on normal working days in Tokyo, in areas without trees.
"Analysis from the samples taken after the hikes in the forest showed significant increases in 'natural killer,' or NK cells, which prevent the formation of tumors; an increase in anticancer proteins in the cells; and a reduction in the concentration of adrenaline in urine, effects which lasted a week after the trips. Alpha and beta pinene (an aerosol released naturally into the air by pine trees) were found in the air in the forest, but not in the city, and the researchers assume phytoncides (germ-killing aerosols released into the air by the trees) to be the active ingredient in the health effects. Other studies of people who have spent time among trees have shown lower concentrations of the stress chemical cortisol, lower pulse rates, lower blood pressure, greater parasympathetic nervous system activity, and less sympathetic activity, which means that people are more relaxed."
Walking among trees makes you feel better. And it also looks like it makes you healthier.