Natural environments and suicide
Authors: Shu-Sen Chang, David Gunnell
Journal: The Lancet Planetary Health (2018)

Suicide is a global public health priority. An estimated 800 000 people die by suicide a year, exceeding deaths by war and homicide combined.1WHOPreventing suicide: a global imperative. World Health Organization, Geneva2014Google Scholar The United Nations Sustainable Development Goals include a target (target 3.4) to "reduce by one third premature mortality from non-communicable diseases through prevention and treatment and promote mental health and well-being"; suicide is one of the two indicators for that target.2WHOMental health: Sustainable Development Goals (SDGs).http://www.who.int/mental_health/suicide-prevention/SDGs/en/Google Scholar With the degradation of the planet due to human activities, rapid urbanisation, and the influence these factors have on the environments in which people live, there is growing evidence of the impact of natural environments on health, including mental health.3Gascon M Triguero-Mas M Martinez D et al.Mental health benefits of long-term exposure to residential green and blue spaces: a systematic review.Int J Environ Res Public Health. 2015; 12: 4354-4379Crossref PubMed Scopus (596) Google Scholar The association of natural environments with population suicide risk is therefore worth exploring. Possible mechanisms underlying any association might include a beneficial effect of natural environments on stress,4Markevych I Schoierer J Hartig T et al.Exploring pathways linking greenspace to health: theoretical and methodological guidance.Environ Res. 2017; 158: 301-317Crossref PubMed Scopus (947) Google Scholar depression5Tomita A Vandormael AM Cuadros D et al.Green environment and incident depression in South Africa: a geospatial analysis and mental health implications in a resource-limited setting.Lancet Planet Health. 2017; 1: e152-e162Summary Full Text Full Text PDF PubMed Scopus (51) Google Scholar and other mental disorders, and social cohesion,4Markevych I Schoierer J Hartig T et al.Exploring pathways linking greenspace to health: theoretical and methodological guidance.Environ Res. 2017; 158: 301-317Crossref PubMed Scopus (947) Google Scholar which are all risk or protective factors of suicide.6Turecki G Brent DA Suicide and suicidal behaviour.Lancet. 2016; 387: 1227-1239Summary Full Text Full Text PDF PubMed Scopus (980) Google Scholar In The Lancet Planetary Health, Marco Helbich and colleagues7Helbich M Beurs Dd Kwan M-P O'Connor R Groenewegen P Natural environments and suicide mortality in the Netherlands: a cross-sectional, ecological study.Lancet Planet Health. 2018; 2: e134-e139Summary Full Text Full Text PDF PubMed Scopus (55) Google Scholar examined the association of outdoor natural environments—as indexed by green space (ie, grass, forests, or parks) and blue space (ie, visible bodies of fresh or salt water) and proximity to the coast—with suicide rates across nearly 400 municipalities in the Netherlands. They reported statistical evidence for lower suicide incidence in municipalities with large or moderate proportions of green space compared with those with less green space. By contrast, no evidence was found for an association of suicide with blue spaces or living near the coast. The study is original in its systematic investigation of three types of natural environments in relation to suicide mortality and its use of advanced spatial analysis methodology. Although the findings resonate with contemporary concerns about the destruction of the natural environment, they need to be interpreted in the context of several caveats. First, this is an ecological, cross-sectional study and the possibility of confounding is substantial. Past research into geographical variations in suicide rates has shown strong associations with area socioeconomic characteristics,8Rehkopf DH Buka SL The association between suicide and the socio-economic characteristics of geographical areas: a systematic review.Psychol Med. 2006; 36: 145-157Crossref PubMed Scopus (306) Google Scholar which in turn are likely to be related to an area's natural environments (eg, poorer areas might be more densely built with fewer green spaces). Helbich and colleagues' findings were notably weakened in the model controlling for potential confounding factors such as unemployment. For example, the unadjusted model showed a 24% reduction in suicide incidence in municipalities with a high level of green space (rate ratio [RR] 0·760, 95% credibility interval 0·681–0·849) whereas the risk reduction halved (12%; 0·879, 0·779–0·991) after adjusting for confounders. Residual confounding (ie, confounding that remains uncontrolled for) is likely because the unemployment variable was based on a one-off measure using data for 2005 whereas the suicide data spanned over the period 2005–14, a time when unemployment rates fluctuated considerably. Furthermore, the study used house prices as an indicator of local economic circumstances, but prices can be affected by the local housing market and the type of housing available, which might vary considerably across areas—eg, between urban and rural areas—and thus might not reflect local economic circumstances as well as other indicators. Other spatial analyses of suicide have used income or deprivation indices, which might better capture socioeconomic deprivation than do house prices, and have generally found strong associations of these deprivation indicators with local suicide incidence.9Hsu CY Chang SS Lee ES Yip PS Geography of suicide in Hong Kong: Spatial patterning, and socioeconomic correlates and inequalities.Soc Sci Med. 2015; 130: 190-203Crossref PubMed Scopus (46) Google Scholar Second, the measures of local levels of green and blue space were based on the amount of land in certain land-use categories (eg, agricultural and natural areas and man-made greenery such as parks for green spaces) in each municipality. Measures based on other indicators such as travelling distance to the exposures of interest might yield different findings,10Guo Y Chang S-S Chen M Yip PSF Do poorer areas have poorer access to services in Hong Kong? A small-area analysis based on multiple spatial accessibility indicators.Soc Ind Res. 2018; (in press).Google Scholar and sensitivity analyses using different availability and accessibility measures of natural environments would aid examination of the robustness of findings. Furthermore, the median municipality population was approximately 25 000, and within area units this populous, there is likely to be very mixed accessibility and proximity to green space. Third, previous studies have indicated access to suicide methods as an important factor contributing to the spatial patterning of suicide.11Chang SS Sterne JA Wheeler BW Lu TH Lin JJ Gunnell D Geography of suicide in Taiwan: spatial patterning and socioeconomic correlates.Health Place. 2011; 17: 641-650Crossref PubMed Scopus (85) Google Scholar For example, suicide by drowning would be more common in coastal areas or regions with major harbours or lakes, which might complicate the association of blue spaces with suicide. In fact, a study12Middleton N Sterne JA Gunnell DJ An atlas of suicide mortality: England and Wales, 1988–1994.Health Place. 2008; 14: 492-506Crossref PubMed Scopus (47) Google Scholar from England and Wales has shown increased suicide incidence in coastal areas. Agricultural areas, where the percentage of farmers and hunters is higher, could see more suicides by firearms.13Skegg K Firth H Gray A Cox B Suicide by occupation: does access to means increase the risk?.Aust N Z J Psychiatry. 2010; 44: 429-434Crossref PubMed Scopus (71) Google Scholar Sensitivity analyses based on suicide by methods whose accessibility does not vary geographically (eg, hanging) could be considered to test the robustness of the suicide–nature association. The authors rightly point out the need for future research to verify the association they found. Useful approaches might include natural experiments (eg, after park construction or loss of green space) or investigations of people who move from one area to another14Wood L Hooper P Foster S Bull F Public green spaces and positive mental health - investigating the relationship between access, quantity and types of parks and mental wellbeing.Health Place. 2017; 48: 63-71Crossref PubMed Scopus (262) Google Scholar to study the effect of natural environments on factors underlying suicide risk such as depression. New evidence in this area could not only contribute to a better understanding of suicide but also have the potential to inform land use and urban planning. For unemployment rates in the Netherlands see https://tradingeconomics.com/netherlands/unemployment-rate For unemployment rates in the Netherlands see https://tradingeconomics.com/netherlands/unemployment-rate We declare no competing interests. Natural environments and suicide mortality in the Netherlands: a cross-sectional, ecological studyOur findings support the notion that exposure to natural environments, particularly to greenery, might have a role in reducing suicide mortality. If confirmed by future studies on an individual level, the consideration of environmental exposures might enrich suicide prevention programmes. Full-Text PDF Open Access