Decades of research point towards a role of urban upbringing in mental health problems, particularly psychosis. Leading theories often refer to the “stress of the city” as a driving factor. Developments in fields spanning geography to genetics call for renewed attention on the topic.
City living and psychosis: An old question
The coronavirus lockdown shone a light on the importance of where we live for our mental health and wellbeing. Do you live in the countryside? Do you have a garden? Do you have friendly neighbours? These factors create very different lockdown experiences, even between neighbours living a stone’s throw apart.
Research into how where we live impacts our mental health is not new. Over eighty years ago in Chicago, Faris and Dunham (1939) found that the incidence of psychotic disorders was considerably higher in the inner city compared to the outskirts. This finding has now been replicated in many cities around the world. If you were raised in a city rather than the countryside, you are 2-3 times more likely to develop a psychotic disorder (Vassos et al., 2010). Today, 55% the world’s population live in urban settings; 70% will do so by 2050 (United Nations, 2019). It is therefore crucial that research tries to unpick how city living affects mental health in order to inform urban planning and mental health provision.
- Lifetime prevalence of 1-3%
- Typically emerge in early adulthood
- Include hallucinations and delusions, anhedonia and apathy, and cognitive symptoms
- Place a huge burden on those affected, their families, and society
Residing in a city from birth to adolescence appears to be particularly important for adulthood psychosis risk, which suggests neurodevelopmental origins. To explore this further, my PhD examined the role of urban upbringing in subclinical psychotic symptoms among children and adolescents, using data from a cohort of 2,232 twins born in England and Wales and followed from birth to age 18: The Environmental Risk (E-Risk) Longitudinal Twin Study. E-Risk families are nationally-representative in terms of their geographic and socioeconomic distribution, meaning the study captures the full range of neighbourhood conditions found in the UK.
Subclinical psychotic symptoms:
- Hallucinations (e.g., hearing voices) and delusions (e.g., paranoia)
- Common among children and teenagers (5-30%)
- Associated with increased adulthood risk for psychotic disorders and other mental health problems
- Lie on a continuum with adult psychotic disorders
Neighbourhood social factors
Cities comprise both affluent and deprived neighbourhoods, but in the UK, urban neighbourhoods tend to be characterised by more deprivation, crime, and social fragmentation compared to rural neighbourhoods. Could neighbourhood social factors explain the urbanicity-psychosis association? Exploring this in the E-Risk Study with my PhD supervisor, Dr Helen Fisher, we found that psychotic symptoms were nearly twice as common among children and teens growing up in cities versus the countryside (Newbury et al., 2016, 2017, 2018). Neighbourhood conditions like high crime and low social cohesion (e.g., weak social connections between neighbours) explained up to 50% of this association. Furthermore, crime victimisation (e.g., muggings and assaults) was more common in cities, and adolescents who had themselves been victimised by violent crime were particularly likely to report psychotic experiences (Newbury et al., 2018). These kinds of exposures are likely to be stressful, and chronic exposure during upbringing could affect neurocognitive development and risk for mental health problems.
Our findings parallel those from previous studies on neighbourhood characteristics and adult psychotic disorders (March et al., 2008). Assuming a causal association, interventions aimed at improving the safety and quality of neighbourhoods in cities could improve the mental health trajectories of our youngest citizens. However, emerging evidence suggests that the urbanicity-psychosis association could be more environmental than social in origin.
New data: Could air pollution play a role?
Air pollution is nowadays largely a man-made problem. Key sources include transport, factories and domestic activity, which explains why pollution is particularly bad in cities. We know that air pollution damages our health. WHO estimates that it causes 4 million premature deaths a year (World Health Organization, 2016). Growing evidence now links air pollution exposure to the brain and mental health (Block et al., 2012).
Developments in air-quality models have been it possible to estimate pollution exposure for large samples down to the address-level. Using this new data in the E-Risk Study, we found that teens exposed to the highest outdoor levels of the gaseous air pollutant, nitrogen dioxide (NO2), had a 71% greater odds for psychotic experiences compared to those living in less polluted neighbourhoods, after adjusting for a range of individual-, family-, and neighbourhood-level factors (Newbury et al., 2019). Levels of NO2 explained a whopping 60% of the association between urban living and psychotic experiences. It is thought that air pollution could increase risk for mental illness by increasing inflammation in the brain and stunting brain development (Block and Calderón-Garcidueñas, 2009). Infants and youth are particularly vulnerable because their brains are rapidly developing. However, the most polluted neighbourhoods are often the most disadvantaged, and this makes it very difficult to tease out the effects of air pollution from those of deprivation and other correlated factors.
More new data: Are findings confounded by genetics?
An enduring question has been whether the association between cities and psychosis is truly causal. Could it in fact be that people at higher genetic risk for mental health problems are more likely to move to cities? The hotbed of this debate has been the consistent finding that the incidence of psychotic disorders is higher among migrant and minority ethnic compared to non-migrant and majority ethnic populations in Northwest Europe. However, given that risk is greatest for second-generation migrants, it is now believed that early-life discrimination and trauma, rather than genetics, explains the elevated risk (Morgan et al., 2010).
In terms of city living, the arrival of polygenic risk scores, which provide an indication of a person’s genetic risk for a particular trait, has made it possible to investigate gene-neighbourhood correlations in large samples. In the E-Risk Study, we recently found that children with higher polygenic risk for schizophrenia and depression were more likely to be raised in urban, deprived, and high-crime neighbourhoods, and move house more frequently when growing up (Newbury et al., 2020). Our findings correspond with some recent reports demonstrating associations between genetic risk for schizophrenia and living in urban and deprived neighbourhoods in adulthood (Sariaslan et al., 2016; Colodro-Conde et al., 2018), and even at birth (Solmi et al., 2020).
Together, the findings could suggest that people at higher genetic risk “drift” downward in social mobility into more crowded and disadvantaged settings, over their lifetime and perhaps across generations. This gene-neighbourhood correlation could confound the observed association between cities and mental health. Notably, in our study, associations between socioenvironmental risk and adolescent psychotic experiences persisted after controlling for genetic risk. However, indices like polygenic risk scores only partially capture genetic variance. The extent that genetics confound the urbanicity-psychosis association remains uncertain.
A key limitation with the research described is that it has been conducted predominantly in Northwest Europe and European-ancestry samples. With over 80% of the world’s population living in Low- and Middle-Income countries (LMICs), this data gap is problematic to say the least. Furthermore, most of the urbanisation projected over coming decades will occur in developing countries, making research into city living and mental health in LMICs even more vital. In fact, fascinating recent evidence suggests that the urbanicity-psychosis association might not exist in LMICs (DeVylder et al., 2018). This raises the intriguing question of whether city living in LMICs might be protective for mental health (or at least less toxic). To explore this further it is crucial that we develop more comprehensive, detailed and valid measures of urban environments in LMIC settings.
Implications and future directions
Given the complexity of cities, the mental health effects of urban living are likely to operate via multiple channels. Neighbourhood social conditions, crime victimisation – and now air pollution – are key contenders, yet to be teased apart. Expanding the research to LMICs will increase our ability to examine which aspects of city living are detrimental – and protective – for mental health. It is likely that genetics contribute to the urbanicity-psychosis association, though the extent of this is not yet known. Crucially, genetic confounding does not mean that interventions are pointless. Understanding the processes leading to gene-neighbourhood correlation could highlight valuable new avenues for interventions to reduce socioeconomic and mental health inequalities.
In the wake of the pandemic, we are told that society will reach a “new normal”. Lockdown brought into sharp relief how much we rely on our neighbourhoods for our mental health and wellbeing. In an urbanising world, we should strive for a new normal that promotes and protects the quality of urban neighbourhoods.
Conflicts of interest
Newbury, J., Arseneault, L., Caspi, A., Moffitt, T. E., Odgers, C. L., & Fisher, H. L. (2016). Why are children in urban neighborhoods at increased risk for psychotic symptoms? Findings from a UK longitudinal cohort study. Schizophrenia Bulletin, 42(6), 1372-1383.
Newbury, J. B., Arseneault, L., Caspi, A., Moffitt, T. E., Odgers, C. L., Baldwin, J. R., Zavos, H. M. S., & Fisher, H. L. (2017). In the eye of the beholder: Perceptions of neighborhood adversity and psychotic experiences in adolescence. Development and Psychopathology, 29(5), 1823-1837.
Newbury, J., Arseneault, L., Caspi, A., Moffitt, T. E., Odgers, C. L., & Fisher, H. L. (2018). Cumulative effects of neighborhood social adversity and personal crime victimization on adolescent psychotic experiences. Schizophrenia Bulletin, 44(2), 348-358.
Newbury, J. B., Arseneault, L., Beevers, S., Kitwiroon, N., Roberts, S., Pariante, C. M., Kelly. F. J., & Fisher, H. L. (2019). Association of air pollution exposure with psychotic experiences during adolescence. JAMA Psychiatry, 76(6), 614-623.
Newbury, J. B., Arseneault, L., Caspi, A., Moffitt, T. E., Odgers, C. L., Belsky, D, W., Sugden, K., Williams, B., Ambler, A. P., Timothy, M., & Fisher, H. L. (2020). Association between genetic and socioenvironmental risk for schizophrenia during upbringing in a UK longitudinal cohort. Psychological Medicine, doi:10.1017/S0033291720003347.
Block, M. L., & Calderón-Garcidueñas, L. (2009). Air pollution: mechanisms of neuroinflammation and CNS disease. Trends in Neurosciences, 32(9), 506-516.
Block, M. L., Elder, A., Auten, R. L., Bilbo, S. D., Chen, H., Chen, J. C., Cory-Slechta, D.A., Costa, D., Diaz-Sanchez, D., Dorman, D.C. & Gold, D. R. (2012). The outdoor air pollution and brain health workshop. Neurotoxicology, 33(5), 972-984.
Colodro-Conde, L., Couvy-Duchesne, B., Whitfield, J. B., Streit, F., Gordon, S., Kemper, K. E., Yengo, L., Zheng, Z., Trzaskowski, M., De Zeeuw, E. L. & Nivard, M. G. (2018). Association between population density and genetic risk for schizophrenia. JAMA Psychiatry, 75(9), 901-910.
DeVylder, J. E., Kelleher, I., Lalane, M., Oh, H., Link, B. G., & Koyanagi, A. (2018). Association of urbanicity with psychosis in low-and middle-income countries. JAMA Psychiatry, 75(7), 678-686.
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March, D., Hatch, S. L., Morgan, C., Kirkbride, J. B., Bresnahan, M., Fearon, P., & Susser, E. (2008). Psychosis and place. Epidemiologic Reviews, 30(1), 84-100.
Morgan, C., Charalambides, M., Hutchinson, G., & Murray, R. M. (2010). Migration, ethnicity, and psychosis: toward a sociodevelopmental model. Schizophrenia Bulletin, 36(4), 655-664.
Sariaslan, A., Fazel, S., D’onofrio, B. M., Långström, N., Larsson, H., Bergen, S. E., Kuja-Halkola, R. & Lichtenstein, P. (2016). Schizophrenia and subsequent neighborhood deprivation: revisiting the social drift hypothesis using population, twin and molecular genetic data. Translational Psychiatry, 6(5), e796-e796.
Solmi, F., Lewis, G., Zammit, S., & Kirkbride, J. B. (2020). Neighborhood characteristics at birth and positive and negative psychotic symptoms in adolescence: Findings from the ALSPAC birth cohort. Schizophrenia Bulletin, 46(3), 581-591.
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