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Factors in Distribution of Multiple Sclerosis

Medically reviewed by Evelyn O. Berman, M.D.
Written by Brooke Dulka, Ph.D.
Posted on May 24, 2021

Multiple sclerosis (MS) is a chronic disease that affects the central nervous system, often leading to several disabling neurological symptoms. Research shows that certain factors affect who is most likely at risk for developing the disease. This branch of research is also known as epidemiology.

Risk factors for MS include gender, race, geography, and genetics. For example, MS seems to appear in some groups, such as white people of northern European ancestry, at a much higher rate than others. Doctors are not yet sure why some people are more likely to develop MS than others, but recent studies have started to provide some clues.

The Geography of Multiple Sclerosis

Multiple sclerosis has a geographical pattern associated with its distribution around the world. This disease traditionally occurs more frequently in areas that are farther from the equator. Neurologists are not yet sure which environmental or genetic risk factors play a role in this pattern. Although some evidence suggests that this geographical pattern may be disappearing over time, the pattern still exists.

One recent study found that the prevalence of MS was highest in high-income areas of North America, Western Europe, Australia, and New Zealand. The study found that the prevalence of MS was lowest in eastern sub-Saharan Africa, central sub-Saharan Africa, and Oceania. These findings may be because there are more doctors available in high-income countries, which means that people may have easier access to an early diagnosis. Easier access to an early diagnosis could be the cause of higher long-term survival rates for people living with MS.

There may also be other reasons why people living in certain places have different rates of MS. UV light can affect the immune system. Additionally, people who live in the same geographic locations tend to share the same sets of genes. People living in places where MS is more prevalent may be more likely to have genes that cause MS.

Gender and Race as Contributing Factors

Sex plays a role in a person’s likelihood of developing MS. Overall, women have much higher prevalence rates of MS — two to three times higher than men. One possible reason for this phenomenon is changing levels of sex hormones in women. Hormones are molecules that act as signals within the body. The sex hormones, such as estrogen and progesterone, play important roles in reproductive development and pregnancy. These hormones may influence the development of MS, especially through their interactions with the immune system. For example, pregnancy has been shown to reduce the severity of MS symptoms. This is sometimes followed by a worsening of symptoms after delivery.

Race or ethnicity may be another important risk factor in developing MS. White people, especially those of northern European descent, are most at risk of developing MS. People of Asian or African descent are at the lowest risk. Neurologists believe that genetic and environmental factors may influence each other in ways that we do not yet understand.

Socioeconomic Status and Multiple Sclerosis

Studies have found that people with a higher socioeconomic status — those who have more income, education, and higher-paying jobs — are more likely to have MS. However, more recent studies have also found the opposite. In these studies, people with a lower socioeconomic status had higher rates of MS. It is not entirely clear why this is. Certain environmental risk factors may play a role. For example, people with higher socioeconomic status may be exposed to fewer germs while growing up. This may lead their immune systems to not work as well later on in life, leading to the high susceptibility of developing a disease like MS.

Multiple Sclerosis: Interaction of Genetics and Environment

Factors such as geography, race, and gender all play a big role in the risk of developing MS. However, MS is a complex interplay of these items that can also be influenced by other factors. For example, a person’s genes and surrounding environment influence the distribution of MS.

The most common risk factors for MS, besides gender, race, and geography, include:

  • Smoking
  • Low vitamin D levels
  • Previous Epstein-Barr virus (EBV) infection
  • Obesity during adolescence
  • Exposure to organic solvents
  • Night shift work

Some of these factors are known to interact with a person's genes. For instance, EBV infection, smoking, and adolescent obesity are known to interact with genes related to the immune system. Because MS is often considered to be an autoimmune disease, the interplay between all these different items can contribute to a higher risk of developing MS.

Research shows changes in vitamin D-related genes could be associated with MS. However, these are complex interactions that scientists and doctors do not yet fully understand and are currently researching.

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MyMSTeam is the social network for people with MS and their loved ones. On MyMSTeam, more than 167,000 members come together to ask questions, give advice, and share their stories with others who understand life with MS.

Are you living with MS? Share your experience in the comments below, or start a conversation by posting on your Activities page.

Posted on May 24, 2021
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Evelyn O. Berman, M.D. is a neurology and pediatric specialist and treats disorders of the brain in children. Review provided by VeriMed Healthcare Network. Learn more about her here.
Brooke Dulka, Ph.D. is a freelance science writer and editor. She received her doctoral training in biological psychology at the University of Tennessee. Learn more about her here.

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