Many Immigrants Face Greater Psychosis Risk

In the AJP study, individuals who made contact with a physician over a seven-year period for a suspected psychotic disorder underwent diagnostic interviews and received DSM-IV diagnoses. Incidence rates for native Dutch and for first- and second-generation immigrants from Morocco, Suriname, and Turkey living in the Hague were calculated.

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.

“High ethnic density” was defined as a neighborhood in which 65 percent of the population consisted of immigrants; because immigrant communities in the Netherlands tend to cluster in the same areas, those neighborhoods were also ones in which the proportion of any one immigrant's ethnic group was substantially represented.

A total of 226 native Dutch and 240 immigrants were diagnosed as having a psychotic disorder. Compared with native Dutch, the adjusted incidence rate ratio for immigrants was significantly increased in low-ethnic-density neighborhoods—that is, neighborhoods in which the diagnosed immigrant's ethnic group was not a significant proportion of the total population.

That incidence rate ratio was 2.36, meaning that immigrants living in neighborhoods of low ethnic density were more than twice as likely to be diagnosed with psychosis as were native Dutch. By comparison, the rate ratio for immigrants living in high-ethnic-density neighborhoods—those where the diagnosed individual's ethnic group was a significant proportion of the population—was just 1.25, meaning that the risk was only fractionally greater than that of native Dutch.

And these findings were consistent for all three ethnic groups. Moroccans had the highest incidence-rate ratio of schizophrenia in both low- and high-density neighborhoods, with a rate ratio of 4.43 in the low-density neighborhoods.

The study, replicating similar research, is one of the most powerful indicators 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, Susser noted.

Veling said he believes the adverse experiences of immigrants living in a community in which their ethnic group is a minority can represent a threat to self-esteem and social identity.

“Individuals may respond to this threat by asserting identification with their group, and by seeking positive distinctiveness,” he said.“ This response has been shown to enhance self-esteem, to prevent or buffer stress, and has been associated with psychological well-being. However, this strong and positive identification is likely to be more difficult to establish for immigrants who live relatively isolated from other members of their ethnic group.”

Veling said the social stress resulting from certain kinds of adverse social experiences is a severe cognitive and emotional challenge, which may exceed the coping ability of individuals with a genetic vulnerability to schizophrenia, who often have impaired executive function. “When subjected to such a severe challenge, they may be more likely to develop the disorder,” he told Psychiatric News.

By contrast, he added, immigrants living in neighborhoods with many others of their own group are likely to have stronger social networks and more social support.

“At the very beginning of the development of psychotic disorder, individuals often have mild and transient psychotic-like symptoms,” Veling said. “If there is no social network, individuals have to explain these experiences themselves and may develop delusions. When they can share their 'strange' experiences with others, they have the opportunity to find normalizing explanations.”

He added that he and colleagues are now conducting a case-control study of first-episode schizophrenia among immigrants to further investigate these mechanisms, with particular focus on the role of ethnic identity, perceived discrimination, acculturation strategies, and social support.

Susser said that pinpointing the social mechanisms in the etiology of schizophrenia among immigrants requires a better understanding of the timing as well as the nature of the exposure. For example, is living in a low-density neighborhood during certain periods of childhood or adolescence particularly important? And research among minority groups who are not immigrants will help to elucidate whether it is simply minority status or the special experience of immigration that accounts for increased risk.

In the meantime, he said, the findings from the Dutch study underscore how important it is for public health officials to pay attention to the mental health needs of immigrants and for clinicians to be culturally sensitive when treating immigrant and minority patients.

“We are seeing a variation in incidence of schizophrenia that would seem to have an underlying social cause to it,” Susser told Psychiatric News. “It points to a disparity that we need to pay attention to, and for individual clinicians it highlights the importance of understanding the cultural context of patients they treat.”

“Ethnic Density of Neighborhoods and Incidence of Psychotic Disorders Among Immigrants” is posted at<http://ajp.psychiatryonline.org/cgi/reprint/appi.ajp.2007.07030423v1>.▪