Multiple sclerosis (MS) does not affect everyone at equal rates. Some people are more likely than others to develop this condition. The study of who gets a particular disease is known as epidemiology. Epidemiology analyzes the distribution, causes, and risk factors of health conditions within specific populations.

When trying to understand epidemiological data, it is helpful to understand the difference between prevalence and incidence rates for multiple sclerosis. Prevalence refers to the number of people who have a disease at a given time. Incidence refers to the number of people who develop a condition during a particular time period. For example, prevalence may tell you how many people currently have MS, whereas incidence may tell you how many new cases of MS are diagnosed each year. Both are considered important measures in epidemiology.

In this article, we will explore who is most likely to develop multiple sclerosis by examining its prevalence and the factors that influence its occurrence, such as geography, age, sex, and ethnicity. We’ll also review the most common risk factors associated with MS. Understanding these factors is crucial for individuals diagnosed with or concerned about MS because they can provide valuable insights into the likelihood of developing the disease, help inform decisions about lifestyle changes, and highlight the importance of early diagnosis and intervention.

What Is the Distribution of Multiple Sclerosis?

Global research shows that the prevalence of multiple sclerosis varies considerably according to several factors: geography, sex, age, and ethnicity.

By Geography

In general, people who live farther away from the Earth’s equator are more likely to develop MS.

Prevalence studies have shown that North American and European countries usually have a higher prevalence of MS (greater than 100 people per 100,000 inhabitants), while Eastern Asian and Sub-Saharan African countries generally have lower rates, often ranging from 5 to 10 people per 100,000 inhabitants. In the United States, MS rates are also higher in the northern half of the country. A study in Spain also noticed that the northwest portion of the country had more cases of multiple sclerosis, further providing evidence for a latitude effect — a pattern also observed in the Southern Hemisphere.

By Sex and Gender

Within the United States, multiple sclerosis prevalence is approximately 450 cases per 100,000 individuals for women and 160 for men, according to research cited in Mayo Clinic Proceedings: Innovations, Quality & Outcomes. This means that women are nearly three times more likely than men to develop MS. Research from other countries also shows significant differences based on sex and gender.

By Age

In the United States, the highest prevalence of multiple sclerosis is found in adults between the ages of 55 and 64, according to studies of age-specific MS prevalence. While MS can affect younger individuals, including children, the disease most commonly affects people in older age groups.

By Race and Ethnicity

Among racial and ethnic groups in the U.S., African Americans have the highest prevalence of multiple sclerosis, followed by white Americans, Hispanic Americans, and Asian Americans, according to research cited in Multiple Sclerosis.

Learn more about how MS affects people of different racial and ethnic groups.

What Causes Multiple Sclerosis?

The causes of multiple sclerosis are largely unknown. MS is an autoimmune disease, meaning that the body’s immune system attacks itself. The immune dysfunction results in demyelination, in which the fatty layer surrounding nerve cells in the brain and spinal cord (called myelin) is gradually destroyed. Demyelination leads to failures in nervous system communication.

Inflammatory factors play a big role in multiple sclerosis. For instance, levels of a protein called tumor necrosis factor-alpha are increased in individuals with multiple sclerosis. This protein may play a role in the demyelination process. Further, interleukin-1 beta (another inflammatory factor) has been shown to cause nerve damage and multiple sclerosis disease progression.

Different gene changes may also play a role. Some studies have found changes in genes that make human leukocyte antigens, the part of a cell’s surface that lets the body know it belongs. More than 100 gene changes have now been identified and associated with multiple sclerosis. Some of these genes may also vary based on a person’s ancestry.

The cause of MS is complicated and involves multiple factors. Scientists widely believe that both genetic and environmental factors contribute to multiple sclerosis disease risk.

What Are the Risk Factors for Multiple Sclerosis?

Several risk factors may increase a person’s chances of developing MS. According to the journal Nature, the most common risk factors include:

• Living at a high latitude
• Being female
• Smoking
• Having low vitamin D levels
• Having an Epstein-Barr virus (EBV) infection
• Having obesity during adolescence
• Being exposed to organic solvents
• Working night shifts regularly

Some of these factors are known to interact with your genes. For instance, EBV infection, smoking, and adolescent obesity interact with human leukocyte antigen risk genes. There is also research that shows variations in genes related to vitamin D are associated with multiple sclerosis.

Connect With Others Who Understand

MyMSTeam is the social network for people with multiple sclerosis and their loved ones. On MyMSTeam, more than 216,000 members come together to ask questions, give advice, and share their stories with others who understand life with multiple sclerosis.

What questions do you have about MS prevalence? Share your experience in the comments below, or start a conversation by posting on your Activities page.