Social Context Returns to Psychosis Research

Today, the study of social context and psychosis is illustrated by research on the effects of paternal age, “urbanicity,” cannabis use, and immigrant and minority status.

Societal factors influence the age at which parents bear children, and older paternal age has been associated with greater risk of psychosis in offspring. The latter is believed to be due to either the accumulation of toxic exposures with aging that affect DNA or simply an increase in errors in DNA replication with aging, Susser said.

Similarly, studies have reported an increased risk of schizophrenia with use of cannabis, as well as a dose-response relationship between cannabis use and psychosis. “Contextual influences on cannabis use include social norms, drug policies, and generational effects,” Susser said.

A number of studies in recent years have indicated that “urbanicity,” or urban living, is associated with an increased risk of psychosis. A prominent theory for explaining the association, Susser said, points to the quantity of “salient events”—intrusive experiences that command attention—associated with urban living and the evidence that schizophrenia may be a disorder of “salience regulation.”

The sheer number of salient events may overwhelm the ability of the at-risk individual to organize and regulate his or her environment, Susser explained.

Some of the most powerful evidence for the influence of social context on psychosis comes from studies of immigration and minority status. A 2005 meta-analysis by Elizabeth Cantor-Graae, Ph.D., and Jean-Paul Selten, Ph.D., M.D., in the American Journal of Psychiatry looked at population-based incidence studies concerning immigrants in the United Kingdom, Netherlands, Denmark, and Sweden appearing between 1977 and 2003 and calculated relative risks for migrant groups for each study.

They found that the mean weighted relative risk for developing schizophrenia among first-generation migrants was 2.7. Subgroup comparisons yielded significantly greater effect sizes for migrants from areas where the majority of the population is black.

Cantor-Graae and Salten concluded that a personal or family history of migration is an important risk factor for schizophrenia and that the differential risk pattern across subgroups suggests a role for psychosocial adversity in the etiology of schizophrenia.

“The association cannot be explained by higher rates of psychosis in the country of origin, selective migration, diagnostic bias, or by differences in pathways to care,” Susser said. “Rather, it would appear to be the effect of something—social networks, language fluency, stigma, discrimination and harassment, or other psychosocial factors—in the experience of being an immigrant or minority.”

A study coauthored by Susser and published in the January 2008 American Journal of Psychiatry examined the role of “ethnic density”—the proportion of a neighborhood population represented by one's own ethnic group—as a possible mediator in the effect of immigration on psychosis risk. The study looked at incidence rates for native Dutch and first- and second-generation immigrants from Morocco, Surinam, and Turkey living in the Hague, Netherlands (Psychiatric News, February 1, 2008).

The ethnic density of a neighborhood was computed for each immigrant group as the proportion of residents belonging to that group, and statistical analysis provided a prediction of the incidence of psychotic disorders as a function of individual ethnicity and neighborhood ethnic density, controlling for other potentially confounding factors.

What Susser and colleagues found was that the risk of schizophrenia in all of the immigrant groups was higher than that for native Dutch, and that for all of the immigrant groups the risk was higher in low-density neighborhoods—that is, in neighborhoods where an immigrant was less likely to be surrounded by others from his or her native country. For Moroccans living in a low-density neighborhood, the risk was almost three times higher than it was for Moroccans living in a high-density neighborhood.

The findings are a powerful indicator of the potential importance of environmental and psychosocial influences in the etiology of schizophrenia, since the effect of ethnic density on risk would appear to admit no other explanation but a social and environmental one.

“What's so interesting about this is that if it is true that ethnic density matters, then it is very difficult to explain it except by some social process—that is, the interactions between yourself and the people around you,” Susser told Psychiatric News in an interview when the study was published. “The most parsimonious explanation for this phenomenon is that it is something in the social life of individuals who develop psychosis that contributes to the increased risk.”

“Schizophrenia and Migration: A Meta-Analysis and Review” is posted at <http://ajp.psychiatryonline.org/cgi/content/full/162/1/12>. “Ethnic Density of Neighborhoods and Incidence of Psychotic Disorders Among Immigrants” is posted at <http://ajp.psychiatryonline.org/cgi/content/full/162/1/12>.