Canada Causes Multiple Sclerosis?!?!
I follow a few MS neurologists on X (or the social media network formerly known as Twitter, which I will always call Twitter, much as the “Rogers Centre” will always be the SkyDome). Today’s tweet from Dr. Brandon Beaber caught my attention: “Canada causes multiple sclerosis”. I needed to know more. I clicked the link to read up on the study.
The study doesn’t actually suggest a causal relationship between living in Canada and developing MS, but it does show strong evidence of a correlation between the portion of a person’s life spent in Canada and the person’s likelihood of developing MS. This brought an expression that I must have heard several hundred times during my undergraduate degree in psychology screaming into my head: “correlation does not imply causation”. Claiming a cause-and-effect relationship from correlational data is an example of the logical fallacy cum hoc ergo propter hoc, or “with this, therefore because of this”. Don’t worry, I’m confident that Dr. Beaber knows this too, but it’s Twitter and being a bit incendiary garners more action on the algorithm, so we’ll forgive him for being a little bit spicy.
The prevalence of MS varies widely between countries. The epidemiological data on MS demonstrates higher prevalence of the disease in countries located farther from the equator, and it is more common in developed countries. Some have suggested a link between the prevalence of MS and “Viking genes”, while others suggest that “Western lifestyles” are to blame for increased prevalence in particular countries. The truth is we don’t really know why MS is more prevalent in one country versus the next. We don’t know what causes MS. Epidemiological data may help to shed light on the cause(s) of MS though, so it is an interesting area of ongoing study.
The MS International Federation maintains the Atlas of MS, which maintains the most comprehensive worldwide data on MS epidemiology. According to the 2020 edition of the Atlas of MS, Canada had the fourth highest prevalence of MS in the world with 290 people living with MS per 100,000 population, behind San Marino (337 per 100,000), Denmark (301 per 100,000), and Germany (300 per 100,000). The United States rounds out the top five countries of MS prevalence (288 per 100,000).
There are some challenges to maintaining accurate epidemiological data, including diagnostic criteria variability, healthcare access, and the availability of diagnostic tools. Is there really less than 1 case of MS per 100,000 population in Cameroon, Ethiopia, and Haiti, for example, or is this a by-product of the global disparity in MRI access? According to a recent research article, approximately 66% of the world does not have access to MRI scanners. There is 1.12 MRI units per million population in low- and middle-income countries, compared to 26.53 MRI units per million population in high-income countries. Does Canada really have a slightly higher prevalence of MS compared with our American neighbours, or are Americans more likely to be uninsured or under-insured compared to us Canucks? While we may have to wait longer for an MRI courtesy of our public healthcare system, we don’t have to decide between an MRI and financial ruin. We have to look at the epidemiological data with an understanding of its limitations. Nonetheless, it is clear that there’s a great deal of variability in MS prevalence between countries, which may help with deciphering the cause(s) of the disease.
The study that prompted Dr. Beaber’s tweet is further evidence of a previously known phenomenon wherein immigrants from a low-MS prevalence country who relocate to a high-MS prevalence country are at an increased risk of developing MS as compared with their risk profile in their country of origin. This cuts both ways. Immigrants from a high-MS prevalence country who relocate to a low-MS prevalence country are at a decreased risk of developing MS as compared with their risk profile in their country of origin. Immigrants to Canada are generally thought to have a lower risk for developing MS than people born in Canada, but a higher risk than those who remain in their country of origin. It was previously thought that the age a person was at the time of relocation mattered. If you relocated as a child, you were more likely to take on the risk profile of the destination country. This study of 1.5 million immigrants to Canada demonstrates that immigrants are increasingly vulnerable to developing MS the longer they have lived in Canada. When comparing a person who has lived in Canada for 20% of their life versus a person who has lived in Canada 70% of their life, the risk for developing MS goes up by about 40%. This is true independent of age, which reflects a change in our understanding of how an immigrant’s risk profile changes. Researchers speculate that this increased risk may stem from lifestyle changes, including adopting a less healthy diet, less exposure to sunlight while living in a Northern climate, and changes to the gut microbiome. While MS has previously been seen as a disease of people of northern European descent, this helps to demonstrate that there is a higher risk of MS in Canada regardless of a person’s background.
No, Canada doesn’t cause MS. However, use of epidemiological data is an important tool in gaining a better understanding of what does cause MS. Risk analysis between high risk and low risk countries, and evaluating changes to risk profiles when immigrating between high risk and low risk countries may unlock a greater understanding of how MS develops.
Tomorrow marks the beginning of MS Awareness Month in Canada. It is just 26 days until the 2024 MS Walk. I’m still a long ways off from my fundraising goal this year, and I hope that you will consider donating to help me reach my goal of raising $5,000 for MS Canada. My heartfelt gratitude to all who have supported me so far. The funds raised by the MS Walk support research on the cause, treatments, and hopefully one day a cure for MS, and support programs that improve the quality of life for Canadians affected by MS. To donate: https://msspwalk.donordrive.com/index.cfm?fuseaction=donorDrive.participant&participantID=41037
