Exposure to Residential Green Space Improves Mental Health

Study finds impressive and immediate mental health improvements as a result of green space exposure

By Kurt Beil, ND, LAc, MPH

Printer Friendly PagePrinter Friendly Page

Reference

Alcock I, White MP, Wheeler BW, Fleming LE, Depledge MH. Longitudinal effects on mental health of moving to greener and less green urban areas. Environ Sci Technol. 2014;48(2):1247-1255.
 

Design

Longitudinal balanced-panel analysis of a 6-year survey with annual datapoints, temporally bisected by a relocation event of participants’ living residential area containing a move to an area of differing quantity of surrounding urban green space (UGS). 
 

Participants

Data were obtained from the British Household Panel Survey (BHPS) about adult participants (N=1,064) living in England who had changed their residential location during the study (1991-2008) to an area of either 1) greater or 2) lesser relative amount of surrounding UGS. Only urban residents were included in order to prevent confounding by other variables (eg, air quality, urban vs rural infrastructure effects). 
 

Study Exposure

Exposure to UGS was determined via standardized British land-use datasets, which were applied to census blocks (lower-layer super output areas [LSOAs]), each containing approximately 1,500 residents. Land-use type was accurate for each 10-m2 area. Percentage of UGS within each residential LSOA was determined, and premove and postmove LSOA UGS were compared.  
 

Outcome Measures

Mental health status was assessed via BHPS General Health Questionnaire (GHQ) data. GHQ is a widely used, 12-item self-report measure of mental health status. Results were inverse-scored (iGHQ) so that higher scores indicated better mental health. A fixed-effects regression model analyzed changes in iGHQ score for 2 consecutive years prior to and 3 consecutive years after a move in residential location. 
 
To control for potential confounders, both LSOA area-level (ie, income, employment, education, and crime rate) and individual level (ie, age, education, marital status, parenting status, household income, work-limiting illness status, employment, residence type, amount of household space, and commuting time) factors were included in the regression model. 
 

Key Findings

Moving to an area of greater UGS produced, as predicted, an immediate increased iGHQ score (b=0.43, P=0.008), reflecting a significant improvement in mental health status above premove baseline. This increase was sustained in the second and third years after the move, suggesting that the improvement to mental health status was permanent and not a reaction to a novel event.   
 
Moving to an area of lesser UGS produced no statistically significant changes in iGHQ score and reflected no changes in mental health status. However, a decrease in iGHQ score was detected for the year-long period prior to the move (b=–0.34, P=0.031). Participants’ iGHQ scores returned to baseline after the move, suggesting that participants habituated to their less-green environments. 
 
Data on motivations for moving (MFM; eg, “wanting more space”, “economic hardship”) were collected but were not incorporated into the regression analysis. However, between-group comparisons demonstrated no significant MFM differences. This suggests that people (as a group) moved to greener or less-green locations for relatively similar reasons, and therefore MFM was likely not a significant factor for between-group iGHQ differences.   
 

Practice Implications

Opportunities to positively influence population mental health status are highly relevant in the current healthcare landscape. Mental health issues affect almost 20% of American adults (26.7% if substance abuse conditions are included1), with 4.8% of the population diagnosed with a serious mental illness.2 The costs of these conditions to the healthcare system and larger society are currently estimated to be between $60 and $100 billion US annually.3 According to a recent analysis reported in The Lancet, mental health disorders are currently the leading cause of disability in the world, with projections suggesting that the prevalence of these conditions will continue to increase.4
 
One determinant of mental health status that has been gaining scientific recognition is the impact of the physical environment, most notably in an area of research investigating what is known as “urban stress.”5 This construct is influenced by many factors (eg, pollution, crowding, crime), but the greater levels of perceived stress reported among urban residents6,7 is one of the most intriguing. Evidence shows that rates of mental distress are known to be higher in urban areas compared to rural counterparts, both in the United States8 and in Western Europe.9 Neural functional magnetic resonance imaging studies have demonstrated significant lasting differences in the amygdala and other stress-related brain regions’ function from exposure to urban vs rural environments.10,11 Like it or not, there may be something fundamentally unhealthy about living in cities. 
In an era in which exposure to nature is losing ground to concrete and computer screens, it is relevant to consider the benefits that the ‘healing power of nature’ may have on individual and population mental health and well-being. 
The evidence for urban stress is particularly concerning given the increasing urbanization of our modern world. Currently, 80% of the US population resides in an urban area, and this number is expected to increase in the coming decades.12 Globally, the population of the planet has been an urban one since 2008, when the 50% mark was passed for percentage of people living in cities around the world.13 This is a major concern for health-minded entities such as the World Health Organization (WHO) that monitor such trends and project that urbanization and its associated health implications will continue to increase.14
 
To address these concerns, experts are advocating a holistic “healthy settings” approach to handle these coming changes. This socioecological perspective, established in the 1986 WHO Ottawa Charter for Health Promotion, creates an understanding that environment is the critical context in which health flourishes “within the settings of [people’s] everyday life; where they learn, work, play and love.”15 As such, much effort is being directed toward health policies that establish urban environments as “healthy places,” as advocated by organization like the WHO and the US Centers for Disease Control and Prevention.16
 
One of the primary areas of attention in the healthy settings approach is the use and/or inclusion of natural environmental features, aka UGS. The literature on the health benefits of UGS is quite extensive,17 and its relationship to the naturopathic profession is both well-established and obvious.18 Since the time of Kneipp, Lust, Lindlahr, and Just, the concept of natural medicine has included immersion in the natural world alongside regimens of whole foods, physical activity, and botanical treatments. Some very compelling studies demonstrate that UGS is an effective remedy for counteracting the negative health effects of urban stress, particularly in disadvantaged socioeconomic populations that are most at risk.19,20 In an era in which exposure to nature is losing ground to concrete and computer screens, it is relevant to consider the benefits that the “healing power of nature” may have on individual and population mental health and well-being. 
 
This study is one of the first to utilize a longitudinal design for demonstrating the healing effects of natural environments. Most of the studies of UGS health effects are snapshots of either acute, single exposures or cross-sectional population studies. This analysis of survey results over a 6-year pre-to-post period shows that changes in UGS can have lasting positive impact on a “shifting baseline” of mental health status. While the quasiexperimental design of the study is not rigorous enough to prove causality, the vast number of confounders adjusted for in the regression models highly suggest that UGS is the factor producing changes in iGHQ score. 
 
Implications of this study are varied. The most obvious is that patients wishing to improve their mental health status may want to consider moving or changing their residence location to a greener area. However, this action is outside of the primary care practitioner’s scope to prescribe (and many patients’ budget to comply). More realistic implications of the study speak to the need for people to have—and for physicians to prescribe—exposure to natural green spaces. This is typically advice well received by a patient, and compliance for this treatment is (anecdotally) quite high. The biophilic response to UGS is well documented for its efficacy in facilitating stress-reduction and mood elevation,21,22 and studies such as this one are beginning to demonstrate the potential effectiveness of UGS for mitigation of mental health concerns and improvement of positive mental well-being. For those interested in addressing the true causes of mental health issues, the results of this study speak to the possibility of adopting a healthy settings approach as part of one’s health promotion. 
 
This study was not without limitations:   
  • As mentioned above, the longitudinal design of the study does not permit causality to be established. However, the only way to experimentally establish causality would be via random assignment of new residential locations to which participants would move. Since it is unlikely that anyone would volunteer to participate in a study in which they had no say in where they were being relocated, the design of the current study is a close as is practically possible to achieving scientific rigor. 
  • The GHQ is a self-report questionnaire. While it is a validated instrument for determining mental health status, it may not be as clinically informative about UGS effects as more specifics measures (eg, the Patient Health Questionnaire-9 for depression, the General Anxiety Disorder scale for anxiety) or diagnoses might be. 
  • The BHPS data only reported on residents of England, limiting generalizability of the findings to that population. 
  • Land-use LSOA data used for determining UGS was taken from a 1-year (2005) dataset. Changes in land-use type (eg, urban development) were therefore not included in the analysis and may limit the validity of the findings. Future studies should utilize annual land-use datasets to correspond to data from participants’ annual health survey.  
 

About the Author

Kurt Beil, ND, LAc, MPH, is a naturopathic and Chinese medicine practitioner in New York’s Hudson Valley region. He completed his postdoctoral research at National University of Natural Medicine's Helfgott Research Institute, where he focused on biomarker and psychometric assessment of the restorative and therapeutic effect of natural environments. He is the founding co-chair of the Health & Nature subcommittee of the Intertwine Alliance, a 150+ member coalition of nonprofits, governmental agencies, and private businesses promoting the parks, trails, and natural areas of the Portland Metro region. Dr Beil speaks and teaches frequently on the health benefits of contact with nature, and maintains a Facebook group (“Naturopaths for Nature”) about this topic. He can be reached via email or at the Hudson Valley Natural Health website

References

  1. Kessler RC, Chiu WT, Demler O, Walters EE. Prevalence, severity, and comorbidity of 12-month DSM-IV disorders in the National Comorbidity Survey Replication. Arch Gen Psychiatry. 2005;62(6):617-627.
  2. US Department of Health and Human Services. Substance Abuse and Mental Health Services Administration. Mental Health, United States, 2010. HHS Publication No. (SMA) 12-4681. Rockville, MD: Substance Abuse and Mental Health Services Administration; 2012.
  3. Soni A. The Five Most Costly Conditions, 1996 and 2006: Estimates for the U.S. Civilian Noninstitutionalized Population. Statistical Brief #248. Rockville, MD: Agency for Healthcare Research and Quality; 2009. Available at: http://meps.ahrq.gov/mepsweb/data_files/publications/st248/stat248.pdf. Accessed June 24, 2014.
  4. Whiteford H, Degenhardt L, Rehm J, et al. Global burden of disease attributable to mental and substance use disorders: findings from the Global Burden of Disease Study 2010. Lancet. 2013;382(9904):1575-1586.
  5. Cappon D. Urban stress. Can Med Assoc J. 1977;116(1):9-10.
  6. Abbott A. Stress and the city: urban decay. Nature. 2012;490(7419):162-164.
  7. Adli M. Urban stress and mental health. Paper presented at: Cities, Health and Well-Being; November, 16-17, 2011; Hong Kong. Available at: http://lsecities.net/media/objects/articles/urban-stress-and-mental-health/en-gb/. Accessed June 24, 2014.
  8. Dhingra SS, Strine TW, Holt JB, Berry JT, Mokdad AH. Rural-urban variations in psychological distress: findings from the Behavioral Risk Factor Surveillance System, 2007. Int J Public Health. 2009;54 Suppl 1:16-22.
  9. Verheij RA, Maas J, Groenewegen PP. Urban–rural health differences and the availability of green space. Eur Urban Reg Stud. 2008;15(4):307-316. 
  10. Lederbogen F, Kirsch P, Haddad L, et al. City living and urban upbringing affect neural social stress processing in humans. Nature. 2011;474(7352):498-501.
  11. Kim TH, Jeong GW, Baek HS, et al. Human brain activation in response to visual stimulation with rural and urban scenery pictures: a functional magnetic resonance imaging study. Sci Total Environ. 2010;408(12):2600-2607.
  12. United States Census Bureau. Growth in urban population outpaces rest of nation, census bureau reports. March 26, 2012. Available at: http://www.census.gov/newsroom/releases/archives/2010_census/cb12-50.html. Accessed June 24, 2014.
  13. United Nations Population Fund. State of World Population 2007: Unleashing the Potential of Urban Growth. New York: United Nations Population Fund; 2007.
  14. World Health Organization Centre for Health Development. Our Cities, Our Health, Our Future: Acting on Social Determinants for Health Equity in Urban Settings. Kobe City, Japan: World Health Organization Centre for Health Development; 2008.
  15. World Health Organization. Ottawa charter for health promotion. Presented at: The International Conference on Health Promotion; November 17-21, 1986; Ottawa, Ontario, Canada.
  16. Centers for Disease Control and Prevention. Designing and building healthy places. Available at:  http://www.cdc.gov/healthyplaces/default.htm. Accessed June 24, 2014.
  17. Gentry BS, Krause D, Tuddenham KA, Barbo S, Rothfuss BD, Rooks C. Improving Human Health by Increasing Access to Natural Areas: Opportunities and Risks: Report of the 2013 Berkley Workshop. New Haven: Yale University Press; 2014.
  18. Beil K. Natural medicine: the healing effects of exposure to nature. Naturopath Doctor News Rev. Available at: http://ndnr.com/nature-cure/natural-medicine-the-healing-effects-of-the-exposure-to-nature/. Accessed June 24, 2014.
  19. Roe JJ, Thompson CW, Aspinall PA, et al. Green space and stress: evidence from cortisol measures in deprived urban communities. Int J Environ Res Public Health. 2013;10(9):4086-4103.
  20. Mitchell R, Popham F. Effect of exposure to natural environment on health inequalities: an observational population study. Lancet. 2008;372(9650):1655-1660.
  21. Bratman GN, Hamilton JP, Daily GC. The impacts of nature experience on human cognitive function and mental health. Ann N Y Acad Sci. 2012 Feb;1249:118-136.
  22. Ulrich RS, Simons RF, Losito BD, Fiorito E, Miles MA, Zelson M. Stress recovery during exposure to natural and urban environments. J Environ Psychol. 1991;11(3):201-230.