Having multiple siblings may reduce the risk of developing multiple sclerosis through early EBV (Infectious Mononucleosis) infection

Is there an association between EBV and multiple sclerosis?

In the article’s introduction, there is a detailed literature review of the possible association between multiple sclerosis and EBV, and there seems to really be one. Having had a prior infection with EBV does not necessarily provide us with an explanation for every single case of multiple sclerosis out there, but there are now more and more studies that have found an association between the two.
The authors of this study report that a third of children are exposed to the EBV virus by the age of two years, and a third by adolescence. It is well known that early exposure is usually asymptomatic (or accompanied by mild symptoms), while delayed exposure (in adolescence), tends to cause more severe illness.
The authors’ hypothesis is similar to others in the medical literature and it proposes that having multiple siblings may bring about a less hygienic environment and earlier exposure to EBV. Early exposure to EBV, in turn, may protects against the development of multiple sclerosis, which seems to be more prevalent in individuals who get EBV when they are older.

The methods

The study compared medical data from Denmark from 1977 to the population registries of people born in Denmark. Infectious mononucleosis and multiple sclerosis cases were noted among families and the number of siblings in those families and the age differences between the siblings were compared. All of this data was, of course, placed into statistical models.

So, did the study establish an association between the number of siblings, EBV exposure and multiple sclerosis?

Yes, it certainly did.
Not only was an association established but the study also found that there was an and protective effective for every additional brother/sister in the family against delayed EBV exposure in adolescence, and by that, a protective effect against multiple sclerosis in adulthood. The study found that the larger the age difference between the siblings, the lower the risk of multiple sclerosis.
Furthermore, the study found that children in kindergarten who had younger siblings were more protected than adolescents who had younger siblings. For example, a 6-year child with a baby brother/sister, is more protected than an adolescent with a baby sibling.

What did the study conclude?

This study really makes you stop and think.
The main conclusion was that it is obvious that early exposure to EBV provides a protective effect against delayed exposure. And this is also in line with the ‘hygiene hypothesis’ that I have mentioned several times in different posts on this website (here’s an example).

Don’t get me wrong. This isn’t 100% accurate. The causes and reasons behind multiple sclerosis may vary and are not only limited to delayed exposure to EBV.
And holding big ‘flu parties’ with children with EBV to encourage its spread is certainly not recommended, regardless of whether or not someone in their family has multiple sclerosis. These parties have not proved to be helpful in any sort of way.

The study has its limitations, of course. It is a retrospective study, that relies on data extrapolated from reports and documentations from medical systems. Many other confounding factors (such as exposure to sun, vitamin D, smoking, genetics, etc.), that are thought to play a role in the development of multiple sclerosis were not studied here.
However, imagine the incentive this study brings about for the development of a vaccine for EBV! If up until now the only reason for developing such a vaccine was to prevent an illness that is ‘simply unpleasant’, now the real goal would be to ‘drastically reduce’ (as the study claims) the prevalence of multiple sclerosis.

And on a personal note, if any one of you was looking for a reason to bring another kid into this world, there – you have one!