Our Paper on Green Environment & Depression Selected as One of the 20 Most Influential Conservation Ecology Papers of 2017 by F1000!
By Colin Butler, F1000 Public Health & Epidemiology Australian National University, Acton, ACT, Australia. The benefits of exposure to green space and health (independent of exercise) is important but contested. In my view, there has been excessive and premature celebration of its virtues. I like contact with green space, especially rich in fresh air and biodiversity. But can such exposure offset important causes of ill-health, such as poverty and discrimination. This paper suggests that may be unlikely, at least in the context of post-apartheid South Africa.
The Tomita, Vandormael and colleagues paper, and a commentary, point out population-level evidence for the benefits of green space is scarce and that most studies have been cross sectional, thus revealing little insight about causation. Simply put, more advantaged groups may be able to afford to live near green space; this proximity to green space could thus be a consequence of health and economic success, rather than a major contributor to well-being.
The authors investigated the effect of a 'green living environment' upon depression in a nationally representative survey in South Africa, using data from over 11,000 people surveyed by the South African National Income Dynamics Study, repeated three times: in 2008; 2010; and 2012. To be included, study participants had to have been assessed for depression risk at least twice in the three surveys. The main outcome was incident depression, assessed by a ten item questionnaire. Green living space was measured by a satellite-derived normalised difference vegetation index based on the GPS coordinates of their dwelling. As the authors state, this is a fairly crude indicator.
At baseline, the cohort studied was free of depressive symptoms. Prevalence of significant depressive symptoms increased to 20.8% by the end of the study. Among poor Africans, the prevalence was about 25%.
The study found an uneven benefit of green space on depression among its participants, with higher green space proximity predicting less incident depression among middle income participants (households with a minimum income of US$1,000 per month, which corresponded to the top quintile in the income distribution) but the reverse pattern among low-income participants, with this particularly evident among African individuals. In other words, for poor South Africans, classified as of African race, proximity to green space was not at all protective against depression over time.
The authors speculate this difference could be in part a legacy of apartheid, and that could be. However, I know from my own past experience of rural general practice in a poor part of Australia that depression and ill health in general are common, despite high exposure to green space. I wonder if a lack of strong protection is more widespread.
The authors speculate that perhaps 'it is only when a person's socioeconomic circumstances have improved, their basic needs been met, and they have moved out of poverty and into the middle class that other apparently non-essential factors such as the greenness of their living environment emerge as potential drivers of depression.'. They conclude that, while people in poverty may still benefit from green space, the struggle for the basics of food, shelter, and security may be of much more importance to wellbeing.
This paper is important as the first study looking at mental health and green space in sub-Saharan Africa. It goes beyond cross sectional studies and the depression data seem well validated. The authors conclude that contact with green space may still be beneficial (especially for those who are at least of middle income), but it is by no means a panacea for poverty and exclusion.
As the commentary {1} noted: 'As urbanisation proceeds at its rapid pace, the temptation is strong to simply translate the existing research into the notion that more green is better.' However, more work is clearly needed. For example, if a government has limited money to spend to improve the health of the poor there may be higher priorities than more green space exposure. In an ideal world, society might choose to do both.
References
1. Commentary - Planning ahead: the mental health value of natural environments
Craig JM, Prescott SL. The Lancet Planetary Health. 2017 Jul; 1(4):e128-e129
DOI: 10.1016/S2542-5196(17)30068-2
News date: 2018-01-24
Links:
http://www.krisp.org.za/manuscripts/Tomita_Vandormael_LancetPlanetHealth.pdf
Publication cited
Unravelling the complicated evolutionary and dissemination history of HIV-1M subtype A lineages. Tongo M, Harkins GW, Dorfman JR, Tovanabutra EBS, de Oliveira T, Martin DP, Virus Evolution (2018), 4(1) doi:vey003/4877091:.
