(P1)..Nature-based physical activity, including countryside walks, hiking, and horseback riding, has been found to be an effective way to improve the health of people with mental illness. A 2005 study showed that walking 35 minutes per day, five times per week, or 60 minutes three times per week significantly improved symptoms of depression. Walking 15 minutes per day did not have such an effect on mood. Other reported symptoms included lower blood pressure, protection against heart disease, and boosting self-esteem. In another study, 20 British participants compared hiking outdoors in a natural setting to walking in an indoor urban shopping mall. Seventy-one percent of those who hiked outside reported a decrease in depressive symptoms while 22% reported increased depression when walking indoors. Ninety percent reported an increase in self-esteem while in nature, and 44% said self-esteem decreased when walking indoors. Many observational and interventional studies show that regular exercise reduces symptoms of depression. In one study, 156 people with depression were divided into three groups; those who did aerobic exercise, those who took the SSRI medicine Zoloft (Sertraline), and those who exercised and took Zoloft. After 16 weeks, all three groups showed an equal response with a 70% improvement of symptoms. The group that took the prescription medicine improved quicker than the group that just did aerobic exercise.