Risk Factors for Developing Multiple Sclerosis

Genes and Your Environment Interacting to Trigger MS

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Risk factors and the question of who gets multiple sclerosis (MS) is a bit complicated. Because researchers do not fully understand the causes of MS, they also do not understand why some people get MS and others do not.

Experts do believe that the development of MS is linked to a complex interaction between a person's DNA (their genes) and their environment. This means that some people are probably genetically vulnerable to developing MS, but only after exposure to something in the environment does that genetic predisposition come to fruition.

What is My Chance of Developing MS?

Your chance of developing MS is small. In fact, the average person in the US has a 1 in 750 chance of getting MS. The National Multiple Sclerosis Society estimates that 400,000 people in the US have been diagnosed with MS, and approximately 200 people are diagnosed with MS in the US each week. Estimates of the number of people living with undiagnosed MS vary widely.

In the world, statistics on MS are difficult to find because MS is a challenging illness to diagnose. That being said, approximately 2.5 million people in the world have MS.

The rates of MS in the US are increasing each year. This could be explained by better diagnostic tests (especially improved MRI scans) and an increased awareness of MS. It may be that many more cases of MS were undiagnosed before MRIs became widely used.

Gender as a Risk Factor for MS

Women are 2 to 3 times more likely than men to become diagnosed with MS, and MS appears to be increasing in frequency in women than men.

Researchers believe that the hormonal differences in men and women account for the higher risk in women -- hormones have a clear interaction with MS and are known to be protective during pregnancy.

Family History of MS as a Risk Factor for MS

If no immediate members of your family have MS, your chances of having MS are 1 in 750.

But, if you have a sibling with MS, your risk increases to 3 to 5 in 100. If you have an identical twin with MS, your risk is about 1 in 3 or 4. It's interesting that identical twins do not always both have MS, even though they share 100 percent of genetic information. This fact is why researchers have concluded that MS is not simply a genetic disease.

Ethnicity and Geography as Risk Factors for MS

MS occurs more often in people of northern European descent, but other ethnicities may also have MS. This could be explained by the fact that MS occurs more frequently in regions that are farther from the equator (above 40 degrees latitude). Rates of MS in these northern regions can be as much as 5 times higher. If a person migrates from a high-risk region to a low risk region before the age of 15, they take on the lower risk. Researchers think that puberty (hormones) and geography may somehow interact to increase MS risk.

There are odd geographical clusters with higher MS rates. Researchers are studying these clusters to learn what factors in the environment may increase MS risk.

So far, nothing has been discovered – but these cluster studies have promise to identify the geographical and environmental risk factors for MS.

Age as a Risk Factor for MS

Most MS is diagnosed between the ages of 20 and 50, thought both childhood and late onset MS are possible. This is usually the age at which the first symptoms appear and a person begins the process of getting diagnosed with MS.

Vitamin D Deficiency as a Risk Factor for MS

Higher  levels of vitamin D, like those greater than 75ng/mL, seem to be protective in developing MS, according to a 2012 study in Neurology. Maintaining a healthy vitamin D level (which we still don't know exactly what that is) may also protect a person against developing MS relapses, once diagnosed.

Smoking as a Risk Factor for MS

Some research shows that smoking increases your risk of developing MS, and this risk may increased the more cigarettes you smoke. This precise connection is still unclear and what exactly it is about smoking that increases the risk.

The Bottom Line

Multiple sclerosis risk factors are tricky and most remain unexplained, although we do know that your genetic makeup and your environmental play a role together. In addition, experts are finding more and more variability within the diagnosis of MS, even within the same type (like relapsing-remitting versus primary-progressive). For example, one person with relapsing-remitting MS may have a dramatically different disease course than someone else with relapsing-remitting MS -- they may respond differently to the same MS disease modifying therapy and have unique types of disability.


Ascherio A & Munger KL. (2007). Environmental risk factors for multiple sclerosis. Part II: Noninfectious factors. Annals of Neurolology, Jun;61(6):504-13.

National Institute of Neurological Disorders and Stroke. Multiple Sclerosis: Hope Through Research ;

National MS Society

Salzer J et al. (2012). Vitamin D as a protective factor in multiple sclerosis. Neurology, Nov 20;79(12):2140-5.

Edited by Dr. Colleen Doherty April 12th 2016.

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