Causes and Risk Factors of Multiple Sclerosis

Causes and risk factors for multiple sclerosis (MS) are complicated. Researchers don't fully understand what precisely brings about MS or why some people get it and others don't.

Several main factors have emerged that appear to play a role, including health of the immune system, infectious diseases, genetics, lifestyle, and others. While each one can explain a piece of the MS puzzle, none can explain everything.

The Immune System

Though no one knows why, most researchers agree that MS is autoimmune, which means the symptoms are caused by the immune system attacking healthy parts of your body as if they were a virus or other infectious agent.

Specifically, in MS, the immune system attacks cells in the brain and spinal cord, damaging the myelin sheath, which is a layer of cells that insulate and influence the function of particular nerves.

The damage impacts how well those nerves function, which is the source of MS symptoms and associated disability. Disease-modifying treatments work by preventing your immune system from attacking the nervous system in this way.

Infectious Diseases

Certain viruses are known to cause damage similar to that of MS. Some researchers believe that infections may somehow trigger the immune system to attack your nerve cells.

Basically, what they suspect is that, to your immune system, the virus or bacterium that causes an initial infection “looks” like a nerve cell. The immune system then develops specialized cells called T-cells to fight off the virus. Those T-cells remain in your body after the infection is gone and appear to become confused when they “see” a nerve cell, mistaking it for an invader. Then they launch an attack.

One virus commonly linked to MS is the Epstein-Barr virus, which causes mononucleosis (a.k.a., mono or "the kissing disease"). This is a very common virus that infects most of us at some point in our lives.

Early exposure to Epstein-Barr may play a role in MS development, but experts simply aren't sure about its role right now .

At this time, no infectious disease (viral, bacterial, or fungal) has been found to definitively cause MS.

Genetics

Researchers believe certain genetic combinations increase the likelihood that you'll develop MS. In fact, scientists have isolated a number of genes that appear to be linked to the disease, most of which are located near the genes linked to your immune system.

In addition to influencing whether you'll get MS, it's possible that your genes may also predict the type of MS you have, how severe it is, and whether you respond well to disease-modifying medications.

Even so, it's important to understand that MS is not a "genetic disease"—meaning there's not a single inherited gene or set of genes that definitively means you'll end up with this illness. Instead, it appears that genes are one factor among many that determine your risk.

Because of this genetic predisposition, your chance of developing MS increases if you have a relative with MS.

The likelihood of you developing MS is approximately:

• 1 in 750 if you have no relatives with MS
• 1 in 50 if you have a parent with MS
• 1 in 20 if you have a sibling with MS
• 1 in 4 if your identical twin has MS

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

Lifestyle

Certain elements of your lifestyle can influence how likely it is that you'll develop MS, including where you live and what you put into your body.

Geography

MS is more common in regions that are farther from the equator, especially above 40 degrees latitude. Rates in these northern regions can be as much as five times higher than in other places.

If you move from a high-risk region to a low-risk region before the age of 15, your risk decreases. Researchers think that puberty hormones may somehow interact with geography to increase MS risk.

It's interesting to note that there are odd geographical clusters with higher MS rates. Researchers are studying them to learn what factors in the environment may be responsible for this, but so far, they haven't come up with much.

Vitamin D Deficiency

Sunlight may play a role in the geographical risk of MS at least in part because people in northern climes are more likely to have a vitamin D deficiency.

Higher levels of vitamin D (those greater than 75ng/mL) seem to help prevent MS, according to a study in Neurology. Maintaining a healthy vitamin D level may also protect people with MS from having relapses, as well.

Research on the role of vitamin D in human health is in its early stages, so it's still not clear exactly how much people should get in a day. However, if you're at high risk for MS, you may want to have your vitamin D levels checked and, if you're deficient, talk to your healthcare provider about the best ways to improve your results.

Other Lifestyle Factors

Other lifestyle factors that scientists have examined as potentially playing a role in MS include:

• A high salt diet
• Obesity (especially in adolescence)
• Smoking

The precise role these elements might play isn't clear, but these are things to consider when trying to lower your risk.

Demographics

Women are 2 to 3 times more likely than men to become diagnosed with MS, and rates in women are increasing faster than they are in men. A 2019 study estimated that in 2017, men accounted for 26 percent of MS cases while women accounted for 74 percent. Researchers believe that the hormonal differences in men and women account for the disparity.

In addition, most MS cases are diagnosed between the ages of 20 and 50, though both childhood and late-onset MS are possible.

Rates of MS

The average person in the United States has a one in 750 chance of getting MS. The National Multiple Sclerosis Society has estimated that approximately 1,000,000 people in the United States have been diagnosed with MS. Estimates of the number of people living with undiagnosed MS vary widely.

The rates of MS in the United States are increasing each year, but that doesn't mean it's becoming more common. At least in part, it's likely due to better diagnostic tests—especially improved magnetic resonance imaging (MRI) scans—and an increased awareness of MS. It may be that many more cases used to go undiagnosed.

Worldwide, reliable statistics are difficult to find because MS is challenging to diagnose. Current estimates are that around 2.5 million people in the world have this disease.