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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.
Global research shows that the prevalence of multiple sclerosis varies considerably according to several factors: geography, sex, age, and ethnicity.
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.
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.
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.
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.
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.
My Identical Sister Has MS Too
Dani Darling and Jacqui Blue, who are triplets along with another sister, have both been diagnosed with relapsing-remitting multiple sclerosis (RRMS).
00:00:00:00 - 00:00:27:15
Dani Darling
When I found out that my sister Jacqui had MS, I was devastated because I had just been diagnosed, so I knew what was happening, and I felt like having gone through it, that was the last thing I wanted was for anyone to go through what I went through.
Jacqui Blue
We are two of three identical triplets.
Dani Darling
Yes, I’m the oldest by one minute.
Jacqui Blue
And I'm the middle, and the oldest of Nikki, our last sister,
00:00:27:15 - 00:00:55:04
Jacqui Blue
by 30 seconds.
Dani Darling
We started making music together
Jacqui Blue
in the womb. [laughing] No, I’m kidding. Like three.
Dani Darling
Before we could even do complete complex sentences, we were harmonizing.
Jacqui Blue
We were singing.
Dani Darling
As triplets, there were a lot of things that we didn’t want to share like, you know, when you’re a kid, you have to split your cake and blow your candles out together. So there’s things that you just don't want to share,
00:00:55:04 - 00:01:15:09
Dani Darling
and I think MS was one of those things.
Jacqui Blue
Dani was diagnosed in September, and then I was diagnosed that next February,
Dani Darling
about six or seven months later, but the thing that we found out was that we’d both had it for years.
Jacqui Blue
Yeah.
00:01:15:11 - 00:01:36:07
Dani Darling
What Nikki has is called RIS, and Jacqui has multiple sclerosis, and I’m not sure when or what her story would have been, or what her diagnosis would have been like if I hadn’t been the first one to find out that I had that. Before we both had it, you were like coaching me in resiliency, like, Jacqui’s a music therapist.
00:01:36:12 - 00:01:59:00
Dani Darling
She was like “You’re going to be OK.” That was actually the most important, I think, factor to me, being able to pick myself up and keep going was that, like, resilience training that you gave me.
Jacqui Blue
Yeah. That’s true. There are steps you can take, and it’s very important, and reaching out for help is one of them. Be honest with your feelings and talking things through.
00:01:59:00 - 00:02:22:22
Jacqui Blue
Stay active mentally and physically active. There are steps you can take to bounce back, and so we are — we’re doing them.
Dani Darling
I’m Dani Darling, and I have relapsing-remitting multiple sclerosis.
Jacqui Blue
I’m Jacqui Blue, and I have relapsing-remitting multiple sclerosis.
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.
Several risk factors may increase a person’s chances of developing MS. According to the journal Nature, the most common risk factors include:
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.
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.
Chiara Rocchi, M.D.
completed medical school and neurology residency at Polytechnic Marche University in Italy.
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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