The association between psychotic disorders and living in urban areas appears to be a reflection of increased social fragmentation present within cities, according to a report in the September issue of Archives of General Psychiatry, one of the JAMA/Archives journals.

"There is a substantial worldwide variation in incidence rates of schizophrenia," the authors write as background in the article. "The clearest geographic pattern within this distribution of rates is that urban areas have a higher incidence of schizophrenia than rural areas." Characteristics of neighborhoods that have been associated with an increased risk of developing psychosis include population and ethnic density, deprivation and social fragmentation or reduced social capital and cohesion.

To examine whether individual, school or area characteristics are associated with psychosis and can explain the association with urbanicity (the quality of being urban), Stanley Zammit, Ph.D., of Cardiff University, Cardiff, Wales, and colleagues studied a total of 203,829 individuals living in Sweden, with data at the individual, school, municipality and county levels.

According to the findings, "the risk of nonaffective psychosis was higher in cities and towns than in rural areas." Of the 203,829 people in the study, 328 (0.16 percent) were ever admitted with a diagnosis of schizophrenia, 741 (0.36 percent) with other nonaffective psychoses, 355 (0.17 percent) with affective psychoses and 953 (0.47 percent) with other psychoses. Additionally, the authors found that almost all variance in the risk of nonaffective psychosis was explained at the individual-level rather than at a higher-level variation. "An association between urbanicity and nonaffective psychosis was explained by higher-level characteristics, primarily school-level social fragmentation." The authors "observed cross-level markers of ethnicity, social fragmentation and deprivation on risk of developing any psychotic disorder, all with qualitative patterns of interaction."

The authors comment that, "being raised in more urbanized areas was associated with an increased risk of developing any nonaffective psychotic disorder." Additionally, "this association was explained primarily by area characteristics rather than by characteristics of the individuals themselves. Social fragmentation was the most important area characteristic that explained the increased risk of psychosis in individuals brought up in cities." The authors also note that, "our findings highlight the concern that physical integration alone is not sufficient but that some of the positive characteristics traditionally conferred by segregation, such as a localized sense of safety, cohesion and community spirit, must also be maintained to enhance the mental health of individuals within the population."

This study was supported by the National Assembly for Wales and Swedish Research Council for Working Life and Social Research.