Frank ties together some very interesting and entertaining links on this topic.
Just one of those is a book by Richard Louv:
… Last Child in the Woods is the first book to bring together a new and growing body of research indicating that direct exposure to nature is essential for healthy childhood development and for the physical and emotional health of children and adults. …
Click through for the details and more links – Our Hiking Blog – Nature Deficit Disorder? Kids at risk without “wild places”?
This is 11yr-old Zach Bonner finishing his 600mi trek from Atlanta to Washington, DC on July 9, 2009
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besthike.com 
I read this book a couple years ago when it first came out, back before it was updated and expanded. We all know how being in a natural place makes us feel, but it’s quite a thing to think that it might be healty for us in a medically measurable way. I do recommend the book.