Triguero-Mas M, Dadvand P, Cirach M, Martinez D, Medina A, Mompart A, Basagana X, Grazuleviciene R, Nieuwenhuijsen MJ. Natural outdoor environments and mental and physical health: relationships and mechanisms. Environ Int. 2015 Apr;77:35-41. doi: 10.1016/j.envint.2015.01.012