Vitamin D, Part 1
Perhaps the biggest mystery in the entire field of MS is why do some people get the disease and others do not? Genetics play a role in who gets the illness, though the role is rather small. In identical twins who share the exact same DNA, if one twin has MS, the chances that the other twin will get MS are still only about 33%.
The Environmental Factor
This means that something in the environment must be a significant factor as well. Epidemiologists have identified several possible factors, including viruses such as Epstein-Barr virus, the virus that causes mononucleosis. One of the most intriguing aspects of MS is that as you move farther away from the equator the incidence of the illness increases. This means the illness is more common in the north in the Northern hemisphere, but more common in the south in the Southern Hemisphere. It matters most where a person spends the first 15 years of their lives, rather than where they are living when they develop the illness. People who grow up near the equator have a very low risk of developing MS.
Though this pattern has been known for decades, no one for sure knows what best
explains this feature of MS. One of the more recent suggestions for this
fact has to deal with sunlight exposure, which in turns is responsible for
levels of vitamin D. The more sunlight exposure one gets, or exposure to
ultraviolet light more specifically, the higher one’s levels of vitamin
D. Vitamin D is most closely associated with bone development, and severe
vitamin D deficiencies lead to a bone disease known as rickets. The
central nervous system converts vitamin D into a biologically active hormone
shown to have anti-inflammatory effects of T-lymphocytes and neuro-protective
functions. This provides a nice explanation for why the rate of MS in Miami is
lower than the rate of MS in Michigan. It also explains why some studies
have found higher rates of MS in patients who live at low altitudes compared to
those who live at high altitudes.
Vitamin D levels have been studied in patients with MS, and indeed patients with MS have been found to have lower levels compared to healthy controls. One study found this to be the case during summer months specifically. This fluctuation in levels of vitamin D might be one reason why relapses in MS have a seasonal variation, being more common in the spring and summer. Despite these findings, it is probably too simplistic to say that low vitamin D levels cause MS. Rather, it is likely to be one of the many factors that interact together to produce the disease in genetically vulnerable individuals.