Multiple Sclerosis Risk Factors

doctor talking to patient

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.

Your chance of developing MS is small. In fact, the average person in the U.S. has a one 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 U.S. 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 U.S. 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.


Women are two to three 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.

Family History

If no immediate members of your family have MS, your chances of having MS are one in 750. But, if you have a sibling with MS, your risk increases to three to five in 100. If you have an identical twin with MS, your risk is about one in three or four.

It's interesting that identical twins do not always both have MS, even though they share 100 percent of their genetic information. This fact is why researchers have concluded that MS is not simply a genetic disease.


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 five 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.

It is interesting to note that 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 much has been discovered.


Most MS is diagnosed between the ages of 20 and 50, though both childhood and late onset MS are possible.

Vitamin D Deficiency

Higher levels of vitamin D, like those greater than 75ng/mL, seem to be protective in developing MS, according to a 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.


Some research shows that smoking increases your risk of developing MS. This precise connection is still unclear and what exactly it is about smoking that increases the risk.

A Word From Verywell

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. 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.

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Article Sources
  • Ascherio A & Munger KL. (2007). Environmental risk factors for multiple sclerosis. Part II: Noninfectious factors. Annals of Neurology, Jun;61(6):504-13.
  • National Institute of Neurological Disorders and Stroke. Multiple Sclerosis: Hope Through Research.
  • National MS Society. What Causes MS?
  • Salzer J et al. (2012). Vitamin D as a protective factor in multiple sclerosis. Neurology, Nov 20;79(12):2140-5.