Causes and risk factors

In a study of more than 10 million US military personnel, the risk of MS rose 32-fold after infection with Epstein-Barr virus (EBV), the virus that causes glandular fever. Most people catch EBV and never get MS, so the virus is thought to be necessary in most cases but not enough on its own.[2]

Low vitamin D is linked to a higher risk of MS, and MS is more common further from the equator. Researchers are studying whether sunlight and vitamin D explain this. The link with geography does not prove the cause.[4]

MS is not passed on by a single gene. A 2019 study found more than 200 genetic variants linked to MS risk, inside and outside the HLA region, with effects that vary in size.[5]

The strongest single genetic risk factor is a version of an immune gene called HLA-DRB1*15:01, which roughly triples the risk. Many people carry it and never develop MS.[6]

Smoking raises the risk of developing MS. It is one of the known risk factors that a person can change.[3]

Obesity during adolescence increases the risk of MS later in life, and the evidence for this has become strong in recent years.[3]

Exposure to organic solvents and shift work have also been linked to a higher risk.[3]

These factors do not act alone. Smoking, EBV infection and obesity in adolescence each interact with the HLA genes that carry the strongest genetic risk, so a person with several of them has a higher risk than the factors would suggest one by one. Researchers read this as a sign that they all act through the same part of the immune system.[3]

Because several of these factors can be changed, prevention has become a research goal in its own right, especially for people at higher risk, such as close relatives of someone with MS. Vaccines against EBV, and early treatment for people whose MRI shows changes before any symptoms, are being tested in trials. The Research section follows this work.[3]