Higher rates of schizophrenia are found in urban areas and it can be attributed to increased deprivation, increased population density and an increase in inequality within a neighborhood, says a new paper.

In common tongue, that used to be called putting the cart before the horse.  A cliché among people who know just enough science to be wrong, you will read 'correlation does not equal causation', and for a more thoughtful examination, you can read how autism can be 'attributed' to the rise if organic food and the Arab spring can be attributed to the price of steel in the same way this study attributes schizophrenia to income inequality, rather than that schizophrenics simply tend to make less money because they are schizophrenic.

How was that determined? Social environment assessments of people who claimed a psychotic disorder. They used data from a population-based incidence study (the East London first-episode psychosis study directed by Professor Jeremy Coid at the East London NHS Foundation Trust and Queen Mary, University of London) conducted in three neighboring inner city, ethnically diverse boroughs of East London: City&Hackney, Newham, and Tower Hamlets.

427 people aged 18-64 years old, all of whom experienced a first episode of psychotic disorder in East London between 1996 and 2000, were assessed about their social environment through measures of the neighborhood in which they lived at the time they first presented to mental health services because of a psychotic disorder. Using the 2001 census, they estimated the population aged 18-64 years old in each neighborhood, and then compared the incidence rate between neighborhoods.  

They concluded that the incidence of schizophrenia (and other similar disorders where hallucinations and delusions are the dominant feature) still showed variation between neighborhoods after taking into account age, sex, ethnicity and social class. Three environmental factors predicted risk of schizophrenia – 'deprivation', such as unemployment, income, education and crime, along with increased population density and an increase in inequality (the gap between the rich and poor).

This suggested that a percentage point increase in either neighborhood inequality or deprivation was associated with an increase in the incidence of schizophrenia and other similar disorders of around 4%. 

Dr. James Kirkbride, principal investigator and lead author of the paper from the University of Cambridge, said, "Our research adds to a wider and growing body of evidence that inequality seems to be important in affecting many health outcomes, now possibly including serious mental illness. Our data seems to suggest that both absolute and relative levels of deprivation predict the incidence of schizophrenia. East London has changed substantially over recent years, not least because of the Olympic regeneration. It would be interesting to repeat this work in the region to see if the same patterns were found."

They further conclude that risk of schizophrenia in some migrant groups might depend on the ethnic composition of their neighborhood. For black African people, they found that rates tended to be lower in neighborhoods where there were a greater proportion of other people of the same background. By contrast, rates of schizophrenia were lower for the black Caribbean group when they lived in more ethnically-integrated neighborhoods. They say the findings support the possibility that the socio-cultural composition of our environment could positively or negatively influence risk of schizophrenia and other similar disorders. 

"Although we already know that schizophrenia tends to be elevated in more urban communities, it was unclear why. Our research suggests that more densely populated, more deprived and less equal communities experience higher rates of schizophrenia and other similar disorders. This is important because other research has shown that many health and social outcomes also tend to be optimal when societies are more equal," said Kirkbride.

Published in Schizophrenia Bulletin.