The odds of developing multiple sclerosis may be higher in people who’ve had infectious mononucleosis and been exposed to low levels of sunlight, a new British study suggests.

Multiple sclerosis is the most common disease of the central nervous system in young adults of Northern European descent, research shows. MS cases are also more common at higher latitudes in temperate climes.

Dr. George Ebers of the University of Oxford and his colleagues found mononucleosis and the effects of exposure to less intense sunlight together explained 72 per cent of the variance in MS prevalence across England.

The study in Tuesday's issue of the journal Neurology also showed the intensity of ultraviolet B exposure, a type of radiation from the sun, alone explained 61 per cent of the difference in MS cases between those living in northern and southern parts of the country.

"When our data are taken in combination with others, it gives confidence that there is a pressing need to investigate the role of vitamin D and [infectious mononucleosis] and their interaction in the pathogenesis of MS," the study authors wrote.

"At present there are no effective vaccines or treatments targeting [Epstein-Barr virus], but their development could complement vitamin D supplementation as potential interventions that might result in a reduction in the prevalence of this often devastating disease."

Vitamin D's role

To come to those conclusions, Ebers' team analyzed hospital records of 56,681 cases of multiple sclerosis and 14,621 cases of mono over seven years, as well as NASA data on UV intensity in England.

Given that our bodies make vitamin D when exposed to UVB, it is possible that vitamin D deficiency may lead to abnormal response to the Epstein-Barr virus, Ebers speculated.

The Epstein-Barr virus is a herpes virus that is extremely common and causes no symptoms in most people. But when teens or adults contract the virus, it can lead to infectious mononucleosis. The role of the virus in MS, if any, remains unclear.

Vitamin D also plays a role in the immune system. Low levels of the vitamin may lead to an abnormal response to Epstein-Barr virus such as infectious mononucleosis, the researchers said.

Great Britain's MS Society, which funded the work, welcomed the findings.

"This work adds weight to existing evidence that MS is caused by a number of factors working in combination. Vitamin D has been closely studied in recent years and is thought to be a key factor in the development of MS; we look forward to seeing more research dedicated to this important area," Dr. Doug Brown, head of biomedical research at the society, said in an email.

The study was also funded by the Medical Research Council and the Wellcome Trust.