Factors that contribute to urban–rural gradients in risk of schizophrenia: Comparing Danish and Western Australian registers

Abstract

Introduction: An association between schizophrenia and urbanicity has long been observed, with studies in many countries, including several from Denmark, reporting that individuals born/raised in densely populated urban settings have an increased risk of developing schizophrenia compared to those born/raised in rural settings. However, these findings have not been replicated in all studies. In particular, a Western Australian study showed a gradient in the opposite direction which disappeared after adjustment for covariates. Given the different findings for Denmark and Western Australia, our aim was to investigate the relationship between schizophrenia and urbanicity in these two regions to determine which factors may be influencing the relationship. Methods: We used population-based cohorts of children born alive between 1980 and 2001 in Western Australia ( N = 428,784) and Denmark ( N = 1,357,874). Children were categorised according to the level of urbanicity of their mother’s residence at time of birth and followed-up through to 30 June 2015. Linkage to State-based registers provided information on schizophrenia diagnosis and a range of covariates. Rates of being diagnosed with schizophrenia for each category of urbanicity were estimated using Cox proportional hazards models adjusted for covariates. Results: During follow-up, 1618 (0.4%) children in Western Australia and 11,875 (0.9%) children in Denmark were diagnosed with schizophrenia. In Western Australia, those born in the most remote areas did not experience lower rates of schizophrenia than those born in the most urban areas (hazard ratio = 1.02 [95% confidence interval: 0.81, 1.29]), unlike their Danish counterparts (hazard ratio = 0.62 [95% confidence interval: 0.58, 0.66]). However, when the Western Australian cohort was restricted to children of non-Aboriginal Indigenous status, results were consistent with Danish findings (hazard ratio = 0.46 [95% confidence interval: 0.29, 0.72]). Discussion: Our study highlights the potential for disadvantaged subgroups to mask the contribution of urban-related risk factors to risk of schizophrenia and the importance of stratified analysis in such cases.

Urbanization and psychosis: an update of recent evidence

“…Urban birth is not a robust risk factor among Aboriginals in Western Australia. The results were consistent with Danish findings only when the cohort was restricted to nonaboriginal indigenous status [19].…”

“…Global studies on urban birth, upbringing, and urbanicity with schizophrenia/psychosis have produced mixed results. Emerging data suggest that urban birth is associated with an increased risk and incidence of schizophrenia [19–21,22 ▪▪ ,23], particularly in the early years of upbringing to 10 years following birth [24]. Some of the studies suggest that the urban birth effect on schizophrenia is mediated by intelligence quotient, as it explained 53% of the total variance [25].…”

“…Global studies on urban birth, upbringing, and urbanicity with schizophrenia/psychosis have produced mixed results. Emerging data suggest that urban birth is associated with an increased risk and incidence of schizophrenia [19][20][21]22…”

Epidemiological Analysis of Mental Health Disorders in Patients at Psychiatric Hospitals in the Special Region of Yogyakarta, Indonesia

“…This is in line with research conducted by McGrath (McGrath et al, 2004) that mental patients are most often found in urban areas. Individuals born, living or raised in densely populated urban environments have a greater risk of developing schizophrenia than those in rural areas (Plana-Ripoll et al, 2021). This is because urban areas are densely populated areas, so they have high levels of poverty, risks of violence, and disease outbreaks that can cause stress (Kristiansson et al, 2015).…”

A Neuroecosocial Perspective on Adolescent Development

“…For example, exposure to crime and violence is higher in deprived neighborhoods, but the type of crime experienced may differ by gender, with females potentially being more exposed to sexual violence and males to gang and physical violence (Scorgie et al 2017). The role of sociocultural identities in the experience of social stressors could further explain why the relationship between urbanicity, social exclusion, and mental health disorders might be more multidirectional in some societies, for example, those that are less unequal or are more multicultural (Heinz et al 2020, Krabbendam et al 2021, Plana-Ripoll et al 2021.…”