Socio-environmental risk factors for schizophrenia include unemployment, low socio-economic status and migration (individual level risk factors) as well as urbanicity, ethnic density and deprivation (neighbourhood level risk factors) .Income inequality is an established social determinant of health in general. The Wilkinsonian hypothesis asserts that health depends on the degree of income inequality in a given society. ie for any given average level of income, the more equally distributed the income is, the higher the average standard of health. Growing body of evidence support this idea. Increasing income inequality is associated with increased infant mortality rates , increased risk for cardiovascular disease , reduced life expectancy and increase in anxiety, depression and suicide .
Do income inequality increase the risk of serious mental disorder like schizophrenia? Jonathan K Burns, Andrew Tomita and Amy S Kapadia investigated ( systematic review) the association between income inequality and incidence of schizophrenia at the level of countries. Studies reporting original data on incidence of schizophrenia in general population were included.Income equality was measured using the Gini coefficient where higher coefficients indicate higher degrees of inequality.
110 studies from a total of 28 countries published between 1975 and 2011 met all inclusion criteria . Mean incidence rates for countries ranged from 5.4 (Norway) to 53.0 (Israel) per 100,000 population. Overall mean and median incidence of schizophrenia for all 107 rates was 18.5 per 100,000 (SD = 11.9; range = 1.7–67.0) and 16 per 100,000, respectively. The mean Gini coefficient for the 26 countries was 33.1 (SD = 6.4; range = 22.8–59.4)
At the country level, there is an association between increasing measures of income inequality and increasing incidence rates of schizophrenia. For every one-point increase in income equality, there was a two-point increase in incidence rate of schizophrenia. Countries characterized by a large rich–poor gap may be at increased risk of schizophrenia.
It is important to note that country-level low SES (e.g. low GDP per capita) does not correlate with median incidence rates of schizophrenia per country i.e. at the ecological level, simple poverty or low economic status may not directly increase risk for schizophrenia. Living in an unequal society does appear to be associated with increased risk for schizophrenia.
Limitations :Quality of incidence data on schizophrenia might vary by country . Apparent relationship between income inequality and risk for schizophrenia is observed at country level, applying at the individual level would be a case of the ‘ecological fallacy”. Individual level data would be needed to overcome this issue.
Conclusions: Income inequality with in a country could increase the risk of schizophrenia at country level.
Comments: The negative effects of income inequality are broader i.e. not specific to schizophrenia. The ill effects of income inequality are not restricted to those at lower ranks,they are experienced by all members of that society regardless of rank. Individual health depends not just on personals income, but also on the incomes of others around. . Effect on social cohesion might explain how unequal societies are more unwell. Politics and policy need to address social determinants of health.
Summary of the article: Income inequality and schizophrenia: Increased schizophrenia incidence in countries with high levels of income inequality. Burns JK, Tomita A, Kapadia AS. Int J Soc Psychiatry. 2014 Mar;60(2):185-96