Residential Green Space in Childhood Is Associated with Lower Risk of Psychiatric Disorders from Adolescence Into Adulthood
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Residential green space in childhood is associated with lower risk of psychiatric disorders from adolescence into adulthood Kristine Engemanna,b,c,1, Carsten Bøcker Pedersenc,d,e, Lars Argef, Constantinos Tsirogiannisf, Preben Bo Mortensenc,d,e, and Jens-Christian Svenninga,b aSection for Ecoinformatics & Biodiversity, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark; bCenter for Biodiversity Dynamics in a Changing World, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark; cCentre for Integrated Register-based Research, Aarhus University, 8210 Aarhus V, Denmark; dNational Centre for Register-based Research, School of Business and Social Sciences, Department of Economics and Business Economics, Aarhus University, 8210 Aarhus V, Denmark; eThe Lundbeck Foundation Initiative for Integrative Psychiatric Research, Aarhus University, 8210 Aarhus V, Denmark; and fCenter for Massive Data Algorithmics, Department of Computer Science, Aarhus University, 8200 Aarhus N, Denmark Edited by Terry Hartig, Uppsala University, Uppsala, Sweden, and accepted by Editorial Board Member Susan T. Fiske January 14, 2019 (received for review May 2, 2018) Urban residence is associated with a higher risk of some psychi- Dose–response relationships from other studies show that atric disorders, but the underlying drivers remain unknown. There higher doses of green space are associated with better mental is increasing evidence that the level of exposure to natural health (13), and long-lasting positive effects of moving to environments impacts mental health, but few large-scale epide- greener areas (18) suggest causation, albeit most of these studies miological studies have assessed the general existence and are small and cross-sectional. Whether the association with importance of such associations. Here, we investigate the pro- green space is specific or applies to a broader spectrum of psy- spective association between green space and mental health in the chiatric disorders and to what degree the association is in- Danish population. Green space presence was assessed at the dependent from urbanization in general or just mirrors the individual level using high-resolution satellite data to calculate the urban−rural gradient are unknown. Access to green space par- SCIENCE × normalized difference vegetation index within a 210 210 m tially depends on socioeconomic factors, such as housing prices, SUSTAINABILITY square around each person’s place of residence (∼1 million people) and the extent to which this explains associations between green from birth to the age of 10. We show that high levels of green space and mental illnesses is another unknown aspect. space presence during childhood are associated with lower risk of Exposure to green space may influence mental health through a wide spectrum of psychiatric disorders later in life. Risk for sub- both psychological and physiological pathways, as green spaces sequent mental illness for those who lived with the lowest level of serve as settings for individual and social behavior and can green space during childhood was up to 55% higher across various mitigate negative influences of other aspects of the physical en- disorders compared with those who lived with the highest level of vironment (19). These mechanistic pathways could vary for different SCIENCES green space. The association remained even after adjusting for psychiatric disorders, with green space as a shared risk-decreasing ENVIRONMENTAL urbanization, socioeconomic factors, parental history of mental illness, and parental age. Stronger association of cumulative green space Significance presence during childhood compared with single-year green space presence suggests that presence throughout childhood is important. Our results show that green space during childhood is associated with Growing up in urban environments is associated with risk of better mental health, supporting efforts to better integrate natural developing psychiatric disorders, but the underlying mecha- environments into urban planning and childhood life. nisms are unknown. Green space can provide mental health benefits and possibly lower risk of psychiatric disorders. This > geographic information systems | mental health | psychological ecosystem nation-wide study covering 900,000 people shows that chil- services | remote sensing | urban planning dren who grew up with the lowest levels of green space had up to 55% higher risk of developing a psychiatric disorder in- dependent from effects of other known risk factors. Stronger he number of people living in cities is increasing, and, glob- association between cumulated green space and risk during Tally, more than 50% of the human population is now city childhood constitutes evidence that prolonged presence of dwellers, with no sign of this trend slowing down (1). Urban living green space is important. Our findings affirm that integrating often offers good sanitation, access to health care, nutrition, and natural environments into urban planning is a promising ap- education (2), but has also been associated with adverse health ef- proach to improve mental health and reduce the rising global fects (3, 4). In some societies, urban residents have almost 50% burden of psychiatric disorders. higher risk of developing psychiatric disorders such as anxiety and mood disorders compared with their rural counterparts (5–7), and Author contributions: K.E., C.B.P., P.B.M., and J.-C.S. designed research; K.E. performed schizophrenia risk is 200% higher for children growing up in the research; L.A. and C.T. contributed new reagents/analytic tools; K.E. analyzed data; and most urban environments (8, 9). Different hypotheses have been K.E., C.B.P., P.B.M., and J.-C.S. wrote the paper. proposed to explain these urban−rural gradients in mental health, The authors declare no conflict of interest. including selective migration (10), social stress processing (4), higher This article is a PNAS Direct Submission. T.H. is a guest editor invited by the Editorial Board. exposure to infections (8), and reduced exposure to nature (11). This open access article is distributed under Creative Commons Attribution-NonCommercial- NoDerivatives License 4.0 (CC BY-NC-ND). However, the mechanistic links are not well understood (5, 12). Data deposition: The NDVI maps used to estimate green space presence are available for Low exposure to nature, or green space, has been proposed in download at https://bios.au.dk/en/about-bioscience/organisation/ecoinformatics-and- recent years as a potential environmental risk factor for various biodiversity/data. mental health outcomes. Exposure to green space has been 1To whom correspondence should be addressed. Email: [email protected]. suggested to lower depression (13, 14) and schizophrenia risk This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. (15), improve children’s cognitive development (16), and re- 1073/pnas.1807504116/-/DCSupplemental. duce neural activity linked to psychiatric disorders (11, 17). www.pnas.org/cgi/doi/10.1073/pnas.1807504116 PNAS Latest Articles | 1of6 factor. Green space can promote mental health by supporting Unadjusted psychological restoration, encouraging exercise, improving social Adjusted urbanization coherence, decreasing noise and air pollution affecting cognition Intellectual disability Adjusted SES Adjusted ALL and brain development, and improving immune functioning (19– Borderline type 22). Given that green space can promote mental health and quality of life in urban populations, urban planning and policy Specific personality disorders will benefit from more information on the likely generality of Anorexia nervosa effects on psychiatric disorders and how those effects are re- alized over the life course. Here, we investigate whether green Eating disorders space presence during childhood is associated with the risk of Obsessive compulsive disorder developing any of a broad range of psychiatric disorders later in life, by combining nationwide population data with individual- Neurotic, stress−related, and somatic disorders level green space presence data. We determine the strength and Single and recurrent depressive disorder shape of the association between green space and a spectrum of mental health outcomes to clarify whether dose–response rela- Recurrent depressive disorder tionships exist and, if this is the case, whether the associations Bipolar disorder are linear or asymptotic. We also examine whether risk of psy- chiatric disorders is more strongly associated with green space Mood disorders presence at a specific age during childhood. Schizoaffective disorder We use data extracted from multiple Danish population-based registers together with high-resolution satellite images. Unlike most Schizophrenia previous studies on green space, the current study includes all Schizophrenia and related disorders members of the national population who met our criteria for in- Cannabis clusion. Our study population thus includes all persons born in Denmark from 1985 to 2003 and living in Denmark on their 10th Alcohol birthdayforwhomwehavelongitudinal data on mental health Substance abuse outcomes, socioeconomic status, and place of residence (n = 943,027). We constructed a dataset of yearly individual-level green Any psychiatric disorder space presence within 210 × 210 m, 330 × 330 m, 570 × 570 m, and 0.81.01.21.41.61.8 930 × 930 m squares around each person’sresidencebasedonthe normalized difference vegetation index (NDVI). NDVI