The cause of multiple sclerosis (MS) is unknown. Scientists have proven that MS is autoimmune in origin. In other words, the damage in MS is caused by the body’s immune system attacking its own tissues, but scientists have not yet figured out why this process begins.

Autoimmune attacks in MS are directed at the tissues of the central nervous system, specifically the myelin sheath that surrounds nerve fibers of the spinal cord, brain, and optic nerve. MS damages the myelin sheath and sometimes the nerve cells as well, leading to MS symptoms like vision problems, spasticity, and muscle weakness.

Although researchers have established that both hereditary and environmental factors influence a person’s risk of developing MS, no one has identified why some people are diagnosed with MS and some aren’t. Most scientists believe MS is most likely caused by a combination of inherited and environmental factors.

Risk Factors for MS

Science is good at finding correlations — or apparent relationships — between factors and disease, but correlation does not prove that the factor causes the disease. Many risk factors for MS have been identified and are being studied, but none has been pinpointed as the cause of MS.

Genetic Factors

MS does not appear to be directly inherited from parents in any clear genetic pattern. However, people with a parent or sibling who has MS have a higher risk of developing the disease. The average person’s risk of developing MS is 0.2 percent.

If someone has a sibling with MS, their risk of developing MS is between 2 percent and 4 percent. In identical twins, if one twin is diagnosed with MS, the other twin has up to a 30 percent chance of developing the condition. Research to better understand genetic susceptibility for MS is ongoing.

Gender

Women are about three times as likely as men to develop MS. In general, there is a greater prevalence of autoimmune disease in females than males. In the United States, 75 percent of those with an autoimmune disease are women.

Women’s immune systems are believed to be more effective than men’s, giving women greater protection from infections, but making them more vulnerable to autoimmune disorders.

Race and Ethnicity

Ethnicity may influence MS predisposition. A research study from Multiple Sclerosis found that MS “has a strong racial and ethnic component and disproportionately affects whites of European background.” It also found that rates are increasing among African Americans, Hispanics, and Asians.

These groups may also experience symptoms differently and vary in the typical age at diagnosis relative to whites. Some ethnic groups, such as the New Zealand Maori and other indigenous peoples, have a low incidence of MS.

Environmental Factors

Researchers have identified a wide array of environmental factors linked to the development of MS.

Geography

One interesting environmental factor, and among the first to be discovered, is geography. The farther a place is from the equator, the more common MS will be. Conversely, MS is very rare in areas near the equator.

Similarly, the farther from the equator someone lives, the earlier they begin experiencing MS symptoms. If a person moves from a lower-risk latitude to a higher-risk latitude in childhood, their risk of developing MS rises accordingly. Moving from a high-risk to a lower-risk area in early life decreases overall risk.

The geographic difference in risk for MS has led scientists to study links between vitamin D and MS. Because people nearer the equator get more sunlight throughout the year, their skin makes more vitamin D.

Studies have established a link between low levels of vitamin D and the development of MS. Current research explores whether vitamin D supplementation can help those who already have MS or prevent the disease from developing by supplementing with vitamin D in childhood.

Some researchers connect the geographic factor with diet. Populations in lower-risk areas tend to live nearer the ocean and consume more fish. Salmon, mackerel, herring, and sardines are rich in vitamin D as well as omega-3 fatty acids, which are believed to reduce inflammation. Diets that are low in saturated fat and emphasize lean protein and fresh produce have been shown to improve MS symptoms.

Smoking

Past or present cigarette smoking makes a woman at least 1.6 times more likely to develop MS, and the risk rises with the number of packs per day. Studies also show that MS progresses more rapidly in those who currently smoke compared to nonsmokers.

Age

Age is a risk factor, with most cases of MS diagnosed between the ages of 20 and 40. It is less common for MS to be diagnosed in older adults and rare for MS to be diagnosed in children. Pediatric cases account for only 2 percent to 5 percent of MS.

Viral Infection

Several studies have investigated specific viruses for links with MS. Some scientists believe that one or more common viruses such as the Epstein-Barr virus (the cause of mononucleosis, or “mono”), varicella-zoster (a herpes virus responsible for chickenpox and shingles), human herpesvirus-6 (cause of roseola), and the measles virus may cause genetic changes in some people, paving the way for the development of MS.

Injury

Researchers have found a correlation between head trauma experienced between ages 10 and 20 and later development of MS. Those who had suffered concussions were more likely to have MS as adults. Multiple concussions further raised the risk.

Seasonal Factors

One study in Finland found that people born in the spring had a higher risk of developing MS. The researchers theorized that women pregnant during the winter received less vitamin D due to lower sun exposure, and the lower levels of vitamin D in the womb may have predisposed their children to develop MS.

Condition Guide

• Multiple Sclerosis (MS) — An Overview
• Multiple Sclerosis Types
• Symptoms of Multiple Sclerosis
• Treatments for Multiple Sclerosis
• Multiple Sclerosis — The Path to Diagnosis