Although the cause of MS is not known, more is being learned about environmental factors that contribute to the risk of developing MS. There is no single risk factor that provokes MS, but several factors are believed to contribute to the overall risk.



Geographic gradient

MS is known to occur more frequently in areas that are farther from the equator. Epidemiologists — scientists who study disease patterns in large groups of people— are looking at variations in geography, demographics (age, gender and ethnic background), genetics, infectious causes and migration patterns in an effort to understand why.



Studies have shown that people born in an area with a low risk of MS who then move — or migrate — to an area with a higher risk before the age of 15 assume the risk of their new area. Such data suggest that exposure to some environmental agent before puberty may predispose a person to develop MS later on.



MS “clusters” — the perception that very high numbers of cases of MS have occurred in a specific time period or location — may provide clues to environmental or genetic risk for the disease. So far, cluster studies in MS have not produced clear evidence for the existence of any causative or triggering factor or factors in MS.



Vitamin D

Growing evidence suggests that vitamin D plays an important role in MS. Low vitamin D levels in the blood have been identified as a risk factor for the development of MS. Some researchers believe that sun exposure (the natural source of Vitamin D) may help to explain the north-south distribution of MS. People who live closer to the equator are exposed to greater amounts of sunlight year-round. As a result, they tend to have higher levels of naturally-produced vitamin D, which is thought to support immune function and may help protect against immune-mediated diseases like MS.



Smoking

The evidence is also growing that smoking plays an important role in MS. Studies have shown that smoking increases a person’s risk of developing MS and is associated with more severe disease and more rapid disease progression. Fortunately, the evidence also suggests that stopping smoking — whether before or after the onset of MS — is associated with a slower progression of disability.



Obesity

Several studies have shown that obesity in childhood and adolescence, particularly in girls, increased the risk of later developing MS. Other studies have shown that obesity in early adulthood may also contribute to an increased risk of developing MS. Also, obesity may contribute to inflammation and more MS activity in those already diagnosed with MS.