The Mental Health Benefits of Nature Exposure
“It is associated with reduced levels of stress — which also has huge ramifications for physical health, reduced levels of depression and anxiety, increased resilience, increased engagement with learning for children and adolescents otherwise disengaged from the education system, improved self-esteem and increased capacity to engage socially”
“As for time in the outdoors, researchers from Nippon Medical School in Japan compared the effects of walking through a forest versus walking through a city. Their results4 show that “forest bathing,” as they call it, not only led to decreased stress hormones, but actually increased the natural killer cells of the immune system and the expression of anti-cancer proteins.”
“the growing disconnection with our natural environment is exacerbating the escalating rates of mental illness and that mental health professionals should be prescribing time in nature as often as possible, as well as advocating on the policy level to help ensure access to green spaces for everyone.”<http://www.psychiatryadvisor.com/mood-disorders/nature-cognitive-anxiety-depression-mood/article/448018/2/>
How Walking in Nature Prevents Depression
Wild environments boost well-being by reducing obsessive, negative thoughts.
Benefits of Ecotherapy: Being In Nature Fights Depression, Improves Mental Health And Well-Being
How walking in Nature Changes the Brain
Stanford researchers find mental health prescription: Nature
The great outdoors: how a green exercise environment can benefit all:
“Our hunter-gatherer ancestors existed with the outdoor natural environment for thousands of years, and it is hypothesised that this provides present day humans with an innate affiliation with nature . In addition, nature provides an environment that does not require our direct attention, giving nature restorative properties therefore allowing recovery from mental fatigue  and attention restoration . Although in the Western world, less people are involved in the natural environment on a daily basis, in particular reduced numbers working on the land, many people seek out nature and undertake outdoor recreational activities. Currently, there is an increasing trend for people to undertake outdoor endurance challenges but, paradoxically, there is a greater proportion of the population with insufficient physical activity levels to meet current health guidelines . Recent reviews indicate that exercising outdoors appears to be more beneficial to mental health over indoor activities  and furthermore, natural environments have a greater impact on psychological health especially when exercise is incorporated . To describe this potential synergistic benefit to health that occurs when exercising whilst being exposed to nature, the term ‘green exercise’ was adopted in 2003  and published through peer-review in 2005″ .
“a strain of bacterium in soil, Mycobacterium vaccae, has been found to trigger the release of seratonin, which in turn elevates mood and decreases anxiety. And on top of that, this little bacterium has been found to improve cognitive function and possibly even treat cancer and other diseases.”
For a great read that includes extensive research on Nature’s benifit’s please read: Last Child in the Woods (great for parents, grandparents, mentors, teachers and mental health professionals). Or his book for adults the Nature Principle, both written by Richard Louv.