The Multiple Sclerosis International Federation (MSIF) has recently released new data on worldwide multiple sclerosis (MS) prevalence, services and more. Researchers gathered this 2013 data from October 2012 to June 2013, updating previous 2008 worldwide data.
The questionnaires they used to collect the data were the same ones used in 2008. The questionnaires were sent to 124 countries and distributed by a country coordinator appointed by the MSIF. Of the 124 countries, 104 completed and returned the questionnaires. This data, in total, covered nearly 80% of the global population.
In general, the researchers found that MS prevalence has increased dramatically in that 5 year span, up 10% and now affecting 2.3 million people worldwide. Whether this is due to a true intrinsic increase in prevalence or whether the condition is being better diagnosed and reported is not clear. For instance, the number of neurologists worldwide have increased by 30%, which might mean that MS is being better diagnosed and reported. Either way, we now know the prevalence is much higher than we previously thought.
MS is a severe autoimmune disease that affects the central nervous system. It is an unpredictable condition that affects each person differently. People with MS may have some or all of the following issues: loss of balance, numbness and weakness, problems speaking, loss of vision, and problems thinking. As the disease progress, these symptoms can force many into a wheelchair.
As covered often here, researchers think that vitamin D may play a strong role in MS, in that research to date shows that (1) vitamin D deficiency increases your risk of MS, and (2) vitamin D supplements can help slow disease onset and progression.
Researchers originally hypothesized that vitamin D plays a role in MS by noticing that the prevalence of MS increased the further you moved away from the equator. Countries far north in latitude don’t get nearly as much sun exposure as countries near or on the equator. And thus, people that live in these northern countries with high MS prevalence rates don’t get nearly as much vitamin D as those closer to the equator.
When we look at the new 2013 data, we see this relationship holds true as ever.
As you can see, while the relationship isn’t perfect, countries generally get darker and darker as we move away from equator, representing higher prevalence of MS per 100,000 people. Canada (291 per 100,000), Norway (160 per 100,000) and Sweden (189 per 100,000) have some of the highest prevalence rates in the world and with being so far north, get some of the least amount of days with sun exposure.
If we take a look at the prevalence country by country, and organized the countries from closest to the equator to furthest, you can see a very clear relationship of higher prevalence as we move further from equator.
You may notice some discrepancies in the data. Some countries further away from the equator, for instance Russia, show low prevalence. Whereas, other countries closer to the equator, for instance Australia, show high prevalence. This might lead you to think that something else is going on; that sun exposure and/or vitamin D have nothing to do with the relationship we see in the map and bar chart.
Yet when we look at prevalence within a specific country – where lifestyle habits and genetics are a bit more homogenous than the entire world population – we still see the same kind of relationship: the states or provinces closest to the equator have lowest prevalence of MS.
Take Australia for example:
The above prevalence data is from a study earlier this year that looked at the number of people receiving drug-moderating treatment for relapsing-remitting MS (this is why prevalence is a little lower than what the global map shows, as it does not include progressive MS prevalence as well). In this country-specific example, there is a very clear relationship: the provinces that are closest to equator have much lower prevalence than the provinces further away.
Another hint why researchers think there is a relationship between vitamin D/sun exposure and MS is that when people move from countries with high prevalence of MS, like the UK for example, down to countries closer to the equator, their risk of developing MS decreases. And vice-versa, when people move to more to northerly regions, their risk of MS increases. Studies of Vietnamese migrants to France showed that the population exhibited higher risk of MS compared to native populations in Vietnam. This suggests that the environment (like a sunnier environment) plays a strong role in the origin of the disease, rather than just genetics.
In summary, the link between MS and geographical region is clear. The large set of recently released data from MSIF illustrates this connection where higher latitudes show higher prevalence of MS. Additionally, when we look at prevalence within a country, we still see the same kind of relationship.
This kind of geographical data, in conjunction with data from cohorts and randomized controlled trials, make it fairly clear that vitamin D deficiency and lack of sun exposure play a role in MS. To what extent, further research will find out. This new data from MSIF, however, shows that the relationship here is as clear as it was 5 to 20 years ago.
Ebers, GC & Sadovnick, AD. The geographic distribution of multiple sclerosis: a review. Neuroepidemiology, 1993.
Hayes CE et al. Vitamin D and Multiple Sclerosis. In Vitamin D: Third Edition by Feldman, Pike, Adams. Academic Press, 2011.
Hollingworth S et al. Pharmacoepidemiology and the Australian regional prevalence of multiple sclerosis. MSJ, 2013.
Multiple Sclerosis International Federation. Atlas of MS Survey. 2013.