Multiple sclerosis (MS) does not affect everyone at equal rates. Some people are more or less likely 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 epidemiology 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.

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 further 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 often have lower rates (approximately two 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 noted 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.

Other scientists support the idea that the geographical gradient is disappearing in the Northern Hemisphere in recent years, suggesting a complex interaction between the environmental and genetic (or hereditary) components of MS.

By Sex

Within the United States, multiple sclerosis prevalence is approximately 450 cases per 100,000 individuals for women and 150 for men. This means that women are nearly three times more likely than men to develop MS. Research from other countries also shows a higher prevalence of MS among women than men.

By Age

People who are between the ages of 55 and 64 are most likely to have multiple sclerosis.

By Ethnicity

MS occurs in most ethnic groups but is more common among white individuals with ancestors from Northern Europe.

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.

The cause of MS is complicated and involves multiple factors. It is now widely believed by scientists 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. The most common risk factors include:

• Living in a region at a high latitude
• Being female
• Smoking
• Having low vitamin D levels in the blood
• Epstein-Barr virus (EBV) infection
• Obesity during adolescence
• Exposure to organic solvents
• Night shift work

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 which shows that variations in genes related to vitamin D are associated with multiple sclerosis.

Finding a Multiple Sclerosis Community

MyMSTeam is the social network for people with multiple sclerosis and their loved ones. On MyMSTeam, more than 165,000 members come together to ask questions, give advice, and share their stories with others who understand life with multiple sclerosis.

Are you living with multiple sclerosis? Share your experience in the comments below, or start a conversation by posting on MyMSTeam.