Multiple Sclerosis in Immigrants: Does Time in Canada Increase Risk?

The risk of developing multiple sclerosis (MS) in immigrants is higher among those who have lived in Canada for a greater part of their lives, according to study results published in Neurology.

Compared with nonimmigrants, immigrants typically have lower rates of cardiovascular disease (CVD), cancer, and MS partly because of a “healthy immigrant effect.” However, this effect may decline over time due to lifestyle changes or other environmental factors, a process called the acculturation effect.

Researchers conducted a population-based retrospective cohort study to explore the relationship between the percentage of life spent in Canada and the risk of developing MS among immigrants to Canada. Outcomes of interest included the incidence of MS among residents aged 20 to 65 in Ontario from January 1, 2003, to December 31, 2016.

The researchers sourced data from multiple linked health and immigrant databases in Ontario, Canada. Participants included immigrants arriving in Ontario before January 1, 2003, with at least 2 years of coverage under the Ontario Health Insurance Program, excluding individuals with a previous MS diagnosis. Researchers also assessed demographic data, immigration-related factors, and comorbidities.

A total of 1.51 million participants were included in the final analysis (49.9% women, mean age, 35.9). Over an average follow-up of 13.9 years, 934 individuals developed new cases of MS coinciding with an incidence rate of 0.44/100,000 person-years.

The average age of immigrants settling in Ontario was 28 years, and on average, they had been in the country for 8 years since their arrival.

The analysis revealed that spending a greater part of life in Canada was associated with an increased risk for MS, with this risk being consistent across genders and immigration categories. The findings were significant for immigrants who arrived at age 15 or younger and lived a substantial portion of their lives in Canada, regardless of their age at migration.

Study limitations included the reliance on health care encounters to define incident MS, which may be influenced by cultural, age, language, and health care system factors.

“Our findings suggest the importance of evaluating the influence of environmental factors on MS risk across the lifespan,” the researchers concluded.

Disclosures: This research was supported by the Institute for Clinical Evaluative Sciences. Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.