Income inequality and schizophrenia: Increased schizophrenia incidence in countries with high levels of income inequality

Abstract

Background—Income inequality is associated with numerous negative health outcomes. There is evidence that ecological level socio-environmental factors may increase risk for schizophrenia. Aims—The aim was to investigate whether measures of income inequality are associated with incidence of schizophrenia at the country level. Method—We conducted a systematic review of incidence rates for schizophrenia, reported between 1975 and 2011. For each country, national measures of income inequality (Gini coefficient) along with covariate risk factors for schizophrenia were obtained. Multilevel mixedeffects Poisson regression was performed to investigate the relationship between Gini coefficients and incidence rates of schizophrenia controlling for covariates. Results—One hundred and seven incidence rates (from 26 countries) were included. Mean incidence of schizophrenia was 18.50 per 100,000 (SD 11.9; range=1.7-67). There was a significant positive relationship between incidence rate of schizophrenia and Gini coefficient (β = 1.02; Z = 2.28; p = 0.02; 95% CI 1.00, 1.03). Conclusions—Countries characterized by a large rich-poor gap may be at increased risk of schizophrenia. We suggest that income inequality impacts negatively on social cohesion, eroding social capital; and that chronic stress associated with living in highly disparate societies places individuals at risk of schizophrenia.