New study finds that some immigrants, refugees in Ontario at higher risk of psychotic disorders

Immigrants from the Caribbean and Bermuda, as well as refugees from East Africa and South Asia, have a 1.5 to 2 times higher risk of psychotic disorders compared to the general population of Ontario, Canada, according to a new study by researchers at the Institute for Clinical Evaluative Sciences (ICES) and the Centre for Addiction and Mental Health (CAMH). The study also found that immigrants from Northern Europe, Southern Europe and East Asia had about half the risk of psychotic disorders compared to the general population.

The study published today in the CMAJ is one of the largest studies of its kind to date.

Ontario is home to the largest number of migrants in Canada, with nearly 30 per cent of the population being a first-generation migrant.

The study linked data from ICES and Citizenship and Immigration Canada to examine nearly four million people between 14 and 40 years of age, following them for 10 years beginning in 1999 to see whether the incidence of psychotic disorders (schizophrenia and schizoaffective disorder) differed between particular migrant groups.

The incidence rate of psychotic disorder was 55.6 per 100,000 person years among the general population, 51.7 per 100,000 person years among immigrants, and 72.8 per 100,000 person years among refugees.

"We found that refugees had about a 25 per cent greater risk of psychotic disorders compared to immigrants. We also found that neighbourhood-level income acted as a protective factor, with migrants who were living in the wealthiest neighbourhoods in the province having half the risk of psychotic disorders compared to migrants living in the poorest neighbourhoods in the province," said Kelly Anderson, lead author and post-doctoral research fellow at ICES Western.

There is substantial evidence from numerous countries to suggest that international migrants are at a higher risk of developing a psychotic disorder compared to the host population, and this risk persists into the second generation. This suggests that something inherent to the migratory or post-migration experience may play a role in the cause of psychotic disorders among these groups.

"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," said Dr. Paul Kurdyak, senior author of the study, Director of CAMH's Health Outcomes and Performance Evaluation Research Unit and lead of the Mental Health and Addictions Research Program at ICES.

"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," said Dr. Kwame McKenzie, one of the study's authors and Medical Director of CAMH's Underserved Populations Program.

Source: Centre for Addiction and Mental Health