A risk factor is something that increases your chance of getting a disease or condition.

It is possible to develop multiple sclerosis (MS) with or without the risk factors listed below. However, the more risk factors you have, the greater your likelihood of developing MS. If you have a number of risk factors, ask your doctor what you can do to reduce your risk.

Risk factors for MS include:

A viral infection may trigger MS. Researchers have been investigating a type of herpes virus, human herpes virus-6, and Epstein-Barr virus. Some medical experts believe that it is the way certain people respond to the virus that may trigger MS.

People who have an isolated attack of optic neuritis (inflammation of the optic nerve) have a high risk of developing MS.

Risk appears to be greatest between the ages of 16 and 40. This is when most people with MS are diagnosed.

At younger ages, women tend to be diagnosed with MS more frequently than men. However, the gender ratio is more equally balanced in people who develop MS later in life.

There may be a genetic component to MS, and sometimes it occurs in families. Researchers suspect more than one gene may be involved.

MS is more common in people of Northern European descent, especially people who are of Scandinavian background.

According to some studies, people with a low intake of vitamin D had an increased risk of MS. But researchers are still investigating vitamin D's role in the development of MS.

If you are concerned about your vitamin D level, talk to your doctor, who can test your blood. Vitamin D can be found in foods like cod liver oil, salmon, mackerel, sardines, and vitamin-D fortified milk. You can also get vitamin D by spending time in the sunshine, which triggers your body to go through a process to produce the vitamin.

Other factors that may increase your risk of MS include:

  • Climate—Living in a colder climate early in life may increase your risk of developing MS. This could be related to getting less sun exposure.
  • Smoking —Smoking is also thought to be associated with a higher risk of MS.