In a U.S. nationwide case study, a team of researchers found evidence for a potential link between viral infections during childhood, vitamin D deficiency, and the risk of developing multiple sclerosis (MS).

The study, “Environmental risk factors associated with pediatric MS: The role of remote viral infections and vitamin D revisited,” was recently presented at the Americas Committee for Treatment and Research in Multiple Sclerosis (ACTRIMS) 2017 Forum, Feb. 23-25 in Orlando, Florida.

“Prior studies have suggested possible associations between viral infection acquired during childhood and vitamin D deficiency and development of MS,” the researchers wrote.

Now, a team investigated this link in a large national case-control study with MS children. Researchers recruited patients with pediatric-onset MS or with clinically isolated syndrome (CIS), a term that describes one of the MS disease courses and is characterized as a first episode of neurological symptoms lasting at least 24 hours.

A total of 360 pediatric MS patients with a mean age of 15.2 years were recruited from 16 pediatric MS centers in the U.S., along with 496 healthy matched controls.

All participants were tested for the presence of several viruses, including Epstein-Barr virus (EBV), cytomegalovirus (CMV), and herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2).

Additionally, researchers assessed vitamin D levels in all participants to identify those with a possible vitamin D deficiency, and identified those who were positive for the human leukocyte antigen (HLA) DRB1*1501 genetic variant, the main genetic factor that’s been implicated in the development of MS.

For CMV, no overall association was found with the risk of pediatric MS. However, an association between HSV-1 , HSV-2, and EBV was found with pediatric MS, especially in patients with a particular background: whites and Hispanic.

“Herpes viruses association with MS risk may be modified by race, ethnicity and DRB1*1501 status,” researchers wrote.

Low vitamin D levels showed no association with MS in patients with a longer disease duration, a phenomenon the researchers attributed to potential vitamin D supplements. In contrast, a potential link between vitamin D deficiency and pediatric MS exists when studied shortly after the onset of the disease.

“Low vitamin D levels may be associated with pediatric MS when looking shortly after disease onset; in patients with longer disease duration this association was not seen, which is likely due to vitamin D supplementation,” the researchers wrote.

The team observed that “for each 1 ng increase in 25(OH) vitamin D serum levels, there was a 3% reduction in the risk of pediatric MS onset.”

“Our preliminary results support an association between prior EBV, HSV-1, and HSV-2 infection, and vitamin D deficiency and development of pediatric-onset MS,” the researchers concluded.

A limitation of the study is that it is a single case-control study, even though 360 pediatric MS patients were recruited, so a definite causal relationship between the patients’ viral status and MS cannot be established. Additional studies are needed.