Summary: A team of researchers led by Dr. Dalia Rotstein (University of Toronto) previously showed that immigrants to Canada have a lower risk of developing multiple sclerosis (MS) compared to long-term residents. In this new study, they found that the risk of MS increased for immigrants as they spent a greater proportion of their lives in Canada. Understanding MS risk factors within the Canadian environment and how they interact to lead to increased risk over time is important and could support efforts towards MS prevention.
Background: Dr. Dalia Rotstein (University of Toronto) and team have shown that although Canada has one of the highest rates of MS in the world, immigrants to Canada, specifically in Ontario, have a lower risk of developing MS compared to long-term residents. This could be due to differences in genetics, lifestyle, and the idea that young, healthy people are more likely to immigrate to a new country (also called the ‘healthy immigrant effect’).
Details: This study aimed to determine whether the risk of MS among immigrants would change with greater proportion of life spent in Canada. The researchers used health administrative data and immigration records from Ontario, Canada to analyze MS risk among 1.5 million immigrants who arrived in Canada between 1985 and 2003. When followed for over 13 years, 934 of these immigrants, originating from different regions of the world (Western countries, South Asia, East Asia, African, Caribbean, Latin America, or Middle East), were diagnosed with MS.
Results: The study showed an association between increased risk of developing MS and greater proportion of time spent in Canada among immigrants.
- Immigrants who had spent a greater proportion of their lives in Canada were more likely to develop MS.
- Migrating at a younger age (15 years or younger) was associated with a more pronounced risk of MS as the proportion of time spent in Canada increased.
- There were no differences in MS risk between male and female immigrants, or among those who belonged to different immigration groups at arrival (e.g., family, refugee, or economic).
- This study did not take into account the effects of biological, environmental or lifestyle factors in the analysis of MS risk.
It is important to note that these results only show an association and do not prove that a greater proportion of time spent in Canada causes MS.
Impact: There are a number of factors associated with MS risk, such as lifestyle (i.e., diet, smoking), environment (i.e., sun exposure, vitamin D levels), and biological factors (i.e., gut microbiome). Findings from this study suggest that adopting these risk factors over time may contribute to the increased risk of MS in immigrants to Canada. Some immigrants may also be more susceptible to these risk factors based on social determinants of health like education, income, environment, and social networks. A better understanding of how these risk factors affect different populations in Canada and how they interact to increase MS risk over time is important and could support efforts towards preventing MS.
Hear Dr. Dalia Rotstein talk more about this research – here.
Reference:
Article published in: Neurology on April 24, 2024 – Proportion of Life Spent in Canada and the Incidence of Multiple Sclerosis in Permanent Immigrants. Link to article – here.