As another limitation of this study, various factors such as deep breathing, differences between forest and urban in ambient illuminance, temperature, and humidity, the inclines and declines during walking and the conditions underfoot while walking, may affect blood serotonin and oxytocin concentrations and symptoms of depression; however, in this study, it was not possible to exclude the influence of some of these factors. The gene discussed is OXT; the disease is depressive symptom measurement.