Dr James Kirkbride, lead author of the study from the University of Cambridge, said: “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.”
The scientists used data from a large population-based incidence study conducted in three neighbouring inner-city, ethnically diverse boroughs in East London: City and Hackney, Newham, and Tower Hamlets.
427 people aged from 18 to 64 were included in the study, all of whom experienced a first episode of psychotic disorder in East London between 1996 and 2000. The researchers assessed their social environment through measures of the neighbourhood 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 neighbourhood, then compared the incidence rate between neighbourhoods. The incidence of schizophrenia, and other similar disorders in which hallucinations and delusions are the dominant feature, still showed variation between neighbourhoods after taking into account age, sex, ethnicity and social class.
Three environmental factors predicted risk of schizophrenia: increased deprivation, which includes employment, income, education and crime; increased population density; and increased inequality, the gap between the rich and poor. Results from the study suggested that a percentage point increase in either neighbourhood inequality or deprivation was associated with an increase in the incidence of schizophrenia and other similar disorders of around 4 per cent.
Dr Kirkbride added: “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 seem 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.”
The study also found that risk of schizophrenia in some migrant groups might depend on the ethnic composition of their neighbourhood. For black African people, the study found that rates tended to be lower in neighbourhoods 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 neighbourhoods. These findings support the possibility that the sociocultural composition of our environment could positively or negatively influence risk of schizophrenia and other similar disorders.
Dr John Williams, Head of Neuroscience and Mental Health at the Wellcome Trust, said: “This research reminds us that we must understand the complex societal factors as well as the neural mechanisms that underpin the onset of mental illness, if we are to develop appropriate interventions.”
The research, led by the University of Cambridge in collaboration with Queen Mary (University of London), was published in the journal ‘Schizophrenia Bulletin’.
Image: ‘Schizophrenia – hearing voices’. Artist’s illustration. Credit: Adrian Cousins, Wellcome Images.
Kirkbride JB et al. Social deprivation, inequality and the neighborhood-level incidence of psychotic syndromes in East London. Schizophrenia Bulletin 2012.