The association between urban living and increased risk for psychosis seen in high-income countries may not generalize to low- and middle-income countries, where 80% of the world’s population lives, new research shows.
Investigators found that urban living was not associated with psychotic experiences or disorders in a large sample of adults from 42 low- and middle-income countries.
These findings, coupled with existing literature, which consists of studies of mainly high-income countries, suggest that the association between urban living and psychosis “may be exclusive to high-income countries,” the investigators write.
“Urban living is one of the most widely replicated social risk factors for psychosis. However, our study shows that it is in fact not a risk factor for psychosis in low- and middle-income countries,” Jordan DeVylder, PhD, of Fordham University in New York City, told Medscape Medical News.
Not a Universal Phenomenon
Most studies of urbanicity and psychosis have been conducted in high-income countries in Europe, North America, or Australia. The association between urban living and psychosis is understudied in low- and middle-income countries (LMICs).
DeVylder and colleagues used cross-sectional survey data from the World Health Organization (WHO) to explore the associations between urban living and psychosis-associated outcomes in 215,682 adults (mean age, 37.9 years; 51% women) in 42 LMICs.
Urban residence was not associated with psychotic experiences, assessed using the WHO Composite International Diagnostic Interview psychosis screen (odds ratio [OR], 0.99; 95% confidence interval [CI], 0.89 – 1.11) or with self-reported lifetime history of a diagnosis of psychotic disorder (OR, 0.89; 95% CI, 0.76 – 1.06), they report.
This finding was true for both low-income countries and middle-income countries. Findings from pooled analyses and meta-analyses of within-country effects also approached a null effect (ie, an OR of 1.00).
These findings suggest that urban living and psychosis risk may not be a universal phenomenon but rather a feature of industrialized countries only, DeVylder and colleagues say.
The authors of a linked editorial note that several of the 42 LMICs included in the study contain densely populated megacities. With the results of this study, “we can confidently reject the hypothesis that living in urban (vs rural) settings is associated with increased risk of psychosis-associated outcomes,” write John McGrath, MD, PhD, of Queensland Brain Institute, Australia, and coauthors.
Several factors have been proposed to explain the increased risk for schizophrenia in urban settings, including increased transmission of infectious agents in densely populated settings, more toxins and pollutants, increased use of drugs, and the notion that people at higher risk for schizophrenia might migrate selectively to larger cities. However, these “candidate risk factors currently lack strong support,” McGrath and colleagues write.
The study by DeVylder and colleagues reinforces findings from a European study published earlier this year in JAMA Psychiatry that found no overall association between urbanicity and the incidence of schizophrenia. When stratified by country, the expected finding linking increased population density and an increased risk for psychosis was identified for England and the Netherlands but not Spain or France, and urban living was found to be a protective factor in Italy. “These are uncomfortable findings,” write McGrath and colleagues.
This study raises more questions than it answers.
Hannah Jongsma, PhD, from the Behavioural and Clinical Neuroscience Institute, University of Cambridge, United Kingdom, who led the European study, said the findings of DeVylder and colleagues are “definitely noteworthy. It is (to my knowledge) the first time the urbanicity hypothesis is tested in LMICs. The study benefits from a large sample size, and a sample drawn from many different countries.”
This study, Jongsma told Medscape Medical News, highlights the importance of context. “There seems to be a difference in what it means to live in an urban area in Western countries and what it means to live in an urban area in LMICs. Maybe absolute and/or relative deprivation are lower in urban compared with rural areas in LMICs,” she said.
Methodologic considerations that are important to consider, said Jongsma, are the use of a binary measure of urbanicity (urban vs rural) and the absence of a continuous index (such as population density). “It is hard to say how rural the rural group is, so there might be some misclassification,” she noted.
Secondly, most studies that examine urbanicity focus on diagnosed psychotic disorders, whereas this study focused on psychotic experiences, a considerably broader category, and on self-reported lifetime psychotic disorders. “There is no indication how accurate reporting of the latter is,” she said.
In Jongsma’s view, this new study “raises more questions than it answers. It illustrates the importance of studying psychosis outside a Western context, of fully understanding the setting you’re studying, and also of paying close attention to the measures used (both outcomes and exposures).”
The study was supported by a Miguel Servet research contract; the Instituto de Salud Carlos III–General Branch Evaluation; and the Promotion of Health Research and the European Regional Development Fund. The authors have disclosed no relevant financial relationships.