2006 June 7, Peter P Groenewegen, Agnes E van den Berg, Sjerp de Vries3 and Robert A Verheij "Vitamin G: effects of green space on health, well-being, and social" BMC Public Health vol. 6 no. 149 →DOI The briefest summary of our program is in its title: Vitamin G, where G stands for the green space around us. Notions of beneficial effects of nearby green space have persisted throughout history.
Source: wiktionary