The mechanism of the health benefit derived from green space(This issue is discussed in a review in PNAS that can be dowloaded here. See the abstract in the next section).
It is well-established that living close to green space reduces overall mortality and cardiovascular disease, and enhances a sense of wellbeing while reducing depressive symptoms. These effects are most striking in people of low socioeconomic status (SES). Why does exposure to green space have this effect?
Some argue that living close to green spaces increases exercise, but this is often untrue. Those living in leafy suburbs may be obliged to take a car to go anywhere at all.
Others argue that the green space may increase social interactions, and so boost “social capital”. This might sometimes be true, but more often multiple other institutions (places of worship, pubs, cafes, community centres, clubs, team sports etc) play this role.
A more common interpretation of the green space effect attributes it to an evolved psychological phenomenon similar to “habitat selection” in other species. We evolved as hunter-gatherers in open spaces, usually following rivers, coast lines and the shores of lakes. Therefore contemplation of such environments might fulfil a psychological need. There is convincing evidence of short term psychological effects following exposure to green spaces. These effects can be proven, not only using psychological testing, but also using portable electroencephalograms, salivary cortisol, blood pressure and a variety of cardiac parameters. So these short-term physiological effects do exist. But are they the crucial explanation for the green space effect?
There are two problems with the psychological work.
- First, it is not clear that short periods of “nature-induced” relaxation (even if repeated at intervals) would cause the long-term effects on survival and wellbeing that are undoubtedly associated with proximity to green spaces.
- Secondly, and more important, is the total lack of controls in the psychological work. The green space exposure is usually compared with exposure to an urban scene or busy urban street. A second control is needed to prove specificity. In other words, would sitting in a quiet bar, listening to background Bach, holding a glass of cold beer have exactly the same effect as the green space?
It could be that the Green Space effect is an additive phenomenon, attributable in part to all three mechanisms suggested above.
However the Old Friends mechanism can add a 4th mechanism that in some ways seems more convincing than the other three, because it can be documented by physiological measures that relate directly to the disorders from which green spaces protect us. We may indeed have evolved to need the psychological input from the natural environment. But just as important, our immune systems have evolved to require inputs from biodiversity of the natural environment, and as other pages explain, this input affects wellbeing, chronic inflammatory disorders, and psychiatric conditions.
Regulation of the immune system by biodiversity from the natural environment: An ecosystem service essential to healthGraham A. Rook
Proc Natl Acad Sci U S A. (2013) 110(46):18360-7. doi:10.1073/pnas.1313731110
Epidemiological studies suggest that living close to the natural environment is associated with long-term health benefits including reduced death rates, reduced cardiovascular disease, and reduced psychiatric problems. This is often attributed to psychological mechanisms, boosted by exercise, social interactions, and sunlight. Compared with urban environments, exposure to green spaces does indeed trigger rapid psychological, physiological, and endocrinological effects. However, there is little evidence that these rapid transient effects cause long-term health benefits or even that they are a specific property of natural environments. Meanwhile, the illnesses that are increasing in high-income countries are associated with failing immunoregulation and poorly regulated inflammatory responses, manifested as chronically raised C-reactive protein and proinflammatory cytokines. This failure of immunoregulation is partly attributable to a lack of exposure to organisms (“Old Friends”) from mankind’s evolutionary past that needed to be tolerated and therefore evolved roles in driving immunoregulatory mechanisms. Some Old Friends (such as helminths and infections picked up at birth that established carrier states) are almost eliminated from the urban environment. This increases our dependence on Old Friends derived from our mothers, other people, animals, and the environment. It is suggested that the requirement for microbial input from the environment to drive immunoregulation is a major component of the beneficial effect of green space, and a neglected ecosystem service that is essential for our well-being. This insight will allow green spaces to be designed to optimize health benefits and will provide impetus from health systems for the preservation of ecosystem biodiversity.
This PNAS review can be downloaded here
See also :-
Flandroy L, Poutahidis T, Berg G, Clarke G, Dao M-C, Decaestecker E, Furman E, Haahtela T, Massart S, Plovier H, Sanz Y, Rook GAW. The impact of human activities and lifestyles on the interlinked microbiota and health of humans and of ecosystems. Science of the Total Environment. 2018;627:1018-38.
This paper analyses parallels between the microbiota of humans, other animals, soil and plants, and discusses the ways in which human activity is damaging microbial biodiversity. It also outlines educational and societal measures that we need to adopt to protect this biodiversity. See abstract of the paper on the “Microbial Biodiversity” page.
Our health and Environmental Microbial Biodiversity:
The health benefits of green space…… psychology or biology?
A paper published by the Centre for Urban Greenery and Ecology (CUGE) in issue #11, pages 50-59 of “CITYGREEN”.
CITYGREEN is an award-winning journal devoted to Ecologically Healthy Cities and to strengthening biodiversity conservation in Singapore
This paper can be downloaded here.
The entire issue #11 of CITYGREEN is available from the CUGE site for 15 Singapore dollars.
This paper explores some of the same issues as the PNAS review, but attempts to explain the arguments in terms comprehensible to non-medical and to non-specialist readers.
OTHER PAPERS: Click on the titles below to reveal the abstract, journal reference and links to the paper
RELEVANT PAPERS FROM OTHER AUTHORS: Click on the titles below to reveal the abstract, journal reference and links to the paper