Speaking purely anecdotally, I can 100% get behind this. I live in a more rural area, work outside regularly, and a large majority of what I eat is either grown locally (without pesticides/herbicides) or I grow it myself. I haven't been to a doctor in 7 or 8 years and am in better shape, and feel better, than I ever have.
Its amazing the difference fresh air, fresh food, and time working in the sun and dirt can make.