Immigrants living in neighborhoods where their own ethnic group represents
a very small proportion of the population may be at increased risk for
That's important because it points to the influence of social
mechanisms—social networks, language fluency, stigma, discrimination and
harassment, and other environmental and psychosocial factors—in the
etiology of some cases of schizophrenia.
This is the conclusion of researchers who studied the effect of"
ethnic density"—the proportion of a neighborhood population
represented by one's own ethnic group—on incidence of psychosis among
immigrant groups in the Hague, Netherlands. Their findings appeared in the
December 2007 American Journal of Psychiatry.
"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," said Ezra Susser, M.D., Dr.P.H., a coauthor of the study in an
interview. "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."
He is chair of the Department of Epidemiology at Columbia University's
Mailman School of Public Health and a professor of psychiatry at the New York
State Psychiatric Institute.
Lead study author Wim Veling, M.D., told Psychiatric News that
immigrants who live in a neighborhood with few others of their own ethnic
group may experience more discrimination, exclusion, and stigma, because they
have more daily contact with the majority population but often have trouble
He added that such a mechanism is consistent with results from a previous
study published in the August 2007 International Journal of
Epidemiology in which Veling and colleagues found a relationship between
ethnic groups' degree of perceived discrimination and the incidence of
psychotic disorder in these groups. Veling is with Parnassia Psychiatric
Institute in the Hague.
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
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
"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
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>.▪