MS Risk Rises with Longer Canadian Residency for Immigrants

A recent study published in the online edition of Neurology®, the medical journal of the American Academy of Neurology, suggests that immigrants to Canada who have spent a larger portion of their lives in the country are at a higher risk of developing multiple sclerosis (MS) compared to those who have spent less time there. However, the study does not establish a causal relationship between increased time in Canada and the development of MS; it only identifies an association.

The research was conducted by Manav V. Vyas, MBBS, MSc, PhD, from St. Michael’s Hospital in Toronto, Canada, who is also a member of the American Academy of Neurology. Vyas and his team sought to investigate whether the generally lower risk of MS among immigrants declines over time as they adopt the lifestyle and environmental factors prevalent in their new country.

The study involved analyzing data from 1.5 million immigrants who arrived in Canada between 1985 and 2003. These immigrants had health insurance coverage for at least two years and had not been diagnosed with MS at the time of their arrival. The researchers then tracked these individuals until 2016 to observe any occurrences of MS.

Among the cohort, 934 individuals were diagnosed with MS during the study period, representing a rate of 0.44 cases per 100,000 person-years. In comparison, the overall rate of MS in Canada, as estimated from previous research, ranges from 15 to 17 cases per 100,000 person-years. Person-years, in this context, indicate both the number of people in the study and the duration of their participation.

To determine the proportion of life spent in Canada, the researchers considered the age at which each immigrant arrived in the country and the duration of their residency. On average, participants had spent approximately 20% of their lives in Canada.

The study revealed a noteworthy correlation between the proportion of life spent in Canada and the risk of developing MS. Individuals who had spent 70% of their lives in Canada were found to be 38% more likely to develop MS compared to those who had spent only 20% of their lives in the country. This association persisted even after adjusting for potential confounding factors such as age, sex, and pre-existing health conditions.

Interestingly, the researchers did not observe any significant differences in MS risk based on gender or immigration class (family, refugee, or economic).

Vyas speculates that various lifestyle and environmental factors could contribute to the increased MS risk among immigrants over time. These factors may include higher rates of smoking, dietary changes, reduced sunlight exposure, and alterations in the gut microbiome composition. Moreover, social determinants of health such as income, education, neighborhood conditions, and access to nutritious food may exacerbate the susceptibility of certain immigrants to these risk factors.

However, the study has certain limitations. For instance, the identification of new MS cases relied on healthcare system records, which may be influenced by cultural, linguistic, or healthcare system-related factors unique to immigrants.

The research received support from the MS Society of Canada and the Consortium of Multiple Sclerosis Centers.

For more information on multiple sclerosis, individuals can visit BrainandLife.org, the official website of the American Academy of Neurology, which offers a free magazine dedicated to patients and caregivers focusing on neurologic disease and brain health. The study findings can also be shared on social media platforms using the hashtags #Neurology and #AANscience.

The American Academy of Neurology, with over 40,000 members, is the world's largest association of neurologists and neuroscience professionals. Its mission is to promote brain health for all and enhance member career fulfillment. Neurologists specialize in diagnosing, treating, and managing disorders of the brain and nervous system, including Alzheimer's disease, stroke, epilepsy, Parkinson's disease, headache, and migraine.