After the "What next?" and the "What is going to happen to me?" type of questions that typically follow diagnosis, eventually most of us living with MS get around to pondering "Why did this happen to me?" We want to know if it was something we did or something that we were exposed to that may have led to us developing MS.
Why people develop MS is still a mystery to researchers. We do know that a variety of risk factors combine to create the "perfect storm" in certain individuals that leads to development of MS.
Two theoretical risk factors that have pretty solid evidence behind them are vitamin D insufficiency and exposure to certain infections.
The EnvIMS study is a large multinational case-control study that looked at people in Italy and Norway. It included 733 people with MS and 1438 controls (people without MS) from Italy and 959 people with MS and 1718 controls from Norway. Researchers collected data on childhood and adolescent sun exposure (sun exposure is necessary for vitamin D production) and sunscreen use by using a self-administered questionnaire. Here is what they found:
In both Italy and Norway, there was a significant association between less sun exposure and developing MS.
In Norway, the association between low exposure to sunlight and MS was strongest in people who reported the lowest amount of sun exposure in the summer between the ages of 16 and 18, while in Italy, the people who reported the least summer sun exposure between the ages of 0 and 5 were the almost twice as likely to have MS.
Interestingly, people who had the highest use of sunscreen in early childhood (0 to 6 years) in Norway were also more likely to have MS.
These findings indicate that there may be an important age variation in sun exposure in relation to MS risk.
Another risk factor that seems to contribute to people's risk of developing MS is infection. While it is very unlikely that infections directly cause MS, it does appear that certain infections may make certain people more likely to develop MS. For instance, Epstein-Barr virus (the virus that causes mononucleosis) increases a person's risk of developing MS by two- or three-fold.
One theory involves certain viruses, called human endogenous retroviridae (HERV). Humans were infected with these viruses millions of years ago and over the ages, the viral DNA became part of the human genome. It is postulated that, under certain conditions, some of these HERV may be able to form infectious virions, which could contribute to that kind of inflammation seen in MS. Research has shown that infections such as Epstein-Barr virus increase the production of HERV virions. It could be that the "right" combination of an infection and particular variant of HERV may lead to MS.
What does this research mean? There is not too much that we can do to prevent contracting Epstein-Barr virus (an estimated 96% of adults in the general population have been infected with EBV). However, sun exposure in early childhood and adolescence may be an important factor in preventing MS in later years. Outdoor activities for young people in all seasons are important for many reasons, and now it looks like lowering risk of MS can be added to the list of benefits. (It should be noted that no one is discouraging sensible use of sunscreen, which should absolutely be applied during the times when the sun is most intense, from 10:00 am to 2:00 pm, especially during the hot months.)