Research conducted in Ontario, Canada, has found that immigrants from Bermuda and the Caribbean and refugees from East Africa and South Asia are up to two times as likely to develop psychotic disorders in comparison with the general population.
Additionally, the researchers found that immigrants from Northern Europe, Southern Europe and East Asia had around half the risk of developing psychotic disorders such as schizophrenia and schizoaffective disorder compared with the general population.
“The pattern we observed in Ontario suggests that psychosocial factors associated with the migratory experience and integration into Canada may contribute to the risk of psychotic disorders,” state the authors.
Published in CMAJ, the study was conducted by researchers from the Institute of Clinical Evaluative Sciences (ICES) and the Center for Addiction and Mental Health (CAMH).
First-generation migrants constitute nearly 30% of the population of Ontario – the largest number of migrants in Canada. According to the study authors, recent data for the province indicates that there are higher rates of hospital admission for psychotic disorders in areas with a large proportion of first-generation migrants.
“The migration-related emergence of psychotic disorders is a potential concern in Canada, which receives about 250,000 new immigrants and refugees each year,” the authors write. “However, there is a notable lack of current epidemiological information on the incidence of psychosis among these groups.”
For the study, the researchers analyzed data from Citizen and Immigration Canada and ICES, following a cohort of 4,284,694 residents of Ontario retrospectively from 1999 for 10 years. Each person followed was between 14 and 40 years of age. During this period, the researchers investigated whether the incidence of psychotic disorders varied between different migrant groups.
Among the general population, the incidence rate of psychotic disorder (schizophrenia and schizoaffective disorder) was 55.6 per 100,000 person-years. The average incidence rate for immigrants was lower at 51.7 per 100,000 person-years respectively, however for refugees the rate was significantly higher at 72.8 per 100,000 person-years.
“We found that refugees had about a 25% greater risk of psychotic disorders compared to immigrants,” reports lead author Kelly Anderson, a postdoctoral research fellow at ICES Western.
“We also found that neighborhood-level income acted as a protective factor, with migrants who were living in the wealthiest neighborhoods in the province having half the risk of psychotic disorders compared to migrants living in the poorest neighborhoods in the province.”
The authors acknowledge their study is limited by the fact that they are unable to assess whether the exposure to urban living or socioeconomically deprived living conditions changed over time for those in the cohort. They state that this distinction may have important implications for the associations discovered during the study.
Evidence from other countries has suggested that, across the world, international migrants face a higher risk of developing psychotic disorders in comparison to host populations. Not only that, but this increased risk has been found to persist into the second generation.
“The patterns we observe suggest that psychosocial factors associated with the migratory experience and integration into Canada may contribute to the risk of psychotic disorders,” states the senior author of the study, Dr. Paul Kurdyak.
These factors include discrimination, adverse and stressful life events, economic hardship and a lack of education. The authors recommend that further research explores potential protective factors in migrant groups with a lower risk of psychotic disorders to help inform support programs for high-risk groups.
“We need to understand why some immigrant groups have lower rates of psychosis. If we know what protects them it will help us develop prevention strategies for all,” states study author Dr. Kwame McKenzie, Medical Director of CAMH’s Underserved Populations Program.
A study conducted earlier this year revealed that several mental disorders – including schizophrenia – are connected by the loss of gray matter in three specific areas of the brain related to cognitive functions.