The map below has two red lines running horizontal that are set at about 40°
latitude north and south. The areas above the north latitude and below the south
latitude are the spots with an overall higher occurrence of multiple sclerosis
(MS). Notice that the majority of North America and Europe to Russia are included
as well as the bottom tip of South America and Australia. The areas inside both
40° lines still have cases of MS, but at a lower overall rate of about 5 to 1.|
Data has shown that MS is especially common in Scotland, Scandinavia, and throughout
northern Europe. In the U.S. the prevalence of MS is higher in whites than in
other racial groups. Studies have shown that it's more common in certain parts
of the world, but if you move from an area with higher risk to one of lower risk
prior to adolescence, then you acquire the risk of your new home location. This
would suggest that exposure to some environmental agent encountered before puberty
may predispose a person to MS.
MS is a disease of temperate climates, meaning the zones in a range of latitudes
between 40° and 60/70°. Not as hot as the subtropical climate and milder than the
polar climate. In both hemispheres, its prevalence increases with distance from
There are many theories as to why MS is more prominent in the areas with greater
temperature variations versus the areas with a more constant temperature. There
are temporal and geographic variations in disease risk, and that risk of disease
may be affected by migration between regions. Numerous potential causal factors
including infection, immunizations, physical and emotional stressors, climate,
diet, and occupational exposures have been studied using various observational
The Blue line indicates the equator and the
two Red lines indicate the 40° latitude mark
It's possible that the colder temperatures cause viruses to spread more rapidly
due to changes in the populations habits. Now if a virus is one of the key
components to MS, and the colder weather keeps the population more closed in,
they may be more likely to pass a virus along, similar to how the influenza
virus is passed in the winter months. With a somewhat large number of the
world's population near and above the 40° north latitude line, it could also be
the close proximity that these groups are to each other all year long. These
areas where involved heavily with the early industrialization of the world,
including heavy refining of metals, petroleum, and the subsequent and various
pollution - most are still involved.
The geographic distribution of MS and the change in risk among migrants also has
provided evidence for the existence of strong environmental determinants of MS.
This can also mean that environmental can also include the various regions
differences in diet and other behaviors.
It's also possible that the consistently warmer areas closer to the equator
allow those populations' to stay a bit further apart from each other. This could
possibly reduce the spreading of these types of viruses. It's also possible that
the later industrialization of these areas has not exposed the populations to
the environmental agents over the period of time needed for the damage to show
up as MS.
Could it be possible that the world's desire for development has given yet
another consequence to our constant need for more? Could it be possible that we
are the ones who are responsible for this and probably many other conditions?
Can MS be another consequence of global warming?
Some scientists think the reason may have something to do with vitamin D, which
the human body produces naturally when the skin is exposed to sunlight. People
who live closer to the equator are exposed to greater amounts of sunlight
year-round. As a result, they tend to have higher levels of naturally-produced
vitamin D, which is thought to have a beneficial impact on immune function and
may help protect against autoimmune diseases like MS.
Some populations like the Inuit never get MS. Native Indians of North and
South America, the Japanese, and other Asian peoples have a very low incident
rate with MS. This would seem to indicate that a genetic barrier may exist in
these groups of people that would protect or prevent MS from developing.
There have also been "epidemics" of MS, such as the time it occurred in a group
of people living off the coast of Denmark after WWII, suggesting an environmental
For those who smoke, it's been shown that they have a 40 to 80% increased
risk of MS compared with those who don't smoke. A study published in
Oxford Journal's Brain of more than 2,000 people with and without MS showed
that smoking may not only increase the risk of developing MS, but in those who
already have MS, smoking may speed progression of the disease and worsen symptoms.