Foreign migration conferred a greater risk for mental illness, researchers reported in JAMA Psychiatry. Among the immigrant population, foreign-born adoptees were at the greatest risk for the whole range of psychiatric disorders.
“A growing number of population-based studies have found increased incidence rates of nonaffective and affective psychoses in first- and second-generation immigrants, firmly establishing a link between foreign migration and higher risk for the development of schizophrenia and other psychotic disorders,” the researchers wrote.
Elizabeth Cantor-Graae, PhD, of Lund University in Sweden, and Carsten B. Pedersen, DMSc, of the University of Århus in Denmark, examined the full range of psychiatric disorders associated with foreign migration in the Danish population, which included foreign-born adoptees, first- and second-generation immigrants, native Danes with a history of foreign residence and those born abroad to Danish expatriates. The researchers obtained the data from the Danish Civil Registration System.
Having a foreign migration background, with the exception of being born abroad to Danish expatriates, was associated with increased risk for at least one psychiatric disorder, according to the researchers. Foreign-born adoptees were at the greatest risk for all psychiatric disorders. For example, the incidence rate ratios (IRRs) among this group for personality disorders was 2.07 (95% CI, 1.90-2.25), 2.15 (95% CI, 1.65-2.75) for bipolar affective disorder , 2.40 (95% CI, 1.47-3.67) for schizoaffective disorder and 2.52 (95% CI, 2.14-2.94) for schizophrenia.
Results also showed that first- and second-generation immigrants were at an almost twofold increased risk for schizophrenia and schizophrenia spectrum disorders. Cantor-Graae and Pedersen found significant differences in the risk for mental illness among first- and second-generation immigrants based on the number of foreign-born parents. For example, those who had two foreign-born parents as opposed to one were particularly vulnerable to schizophrenia and schizophrenia spectrum disorders, a finding the researchers described as “paradoxical.”
However, second-generation immigrants were at a significantly increased risk for all psychiatric disorders.
Finally, native Danes with a history of foreign residence were at increased risk for bipolar affective disorder (IRR=1.54; 95% CI, 1.16-1.99), affective disorders (IRR=1.17; 95% CI, 1.07-1.28), personality disorders (IRR=1.18; 95% CI, 1.06-1.30) and schizophrenia spectrum disorders (IRR=1.31; 95% CI, 1.11-1.54).
According to the researchers, the relationship between foreign migration and greater risk for psychiatric illness can be attributed to a number of factors, including racial or ethnic density, barriers to seeking mental health care, psychosocial adversity or even biological factors.
“Considering the broad range of psychiatric outcomes studied, it would be difficult to draw any conclusions about the extent to which the elevated risk for psychiatric disorders associated with migration is mostly due to exposure to social adversity, other types of nongenetic factors, or aspects of parental vulnerability,” they wrote. “The extent to which parental choice of residence per se might be influenced by genetic determinants cannot be entirely ruled out as a contributing factor.”
Disclosure: The researchers report no relevant financial disclosures.