Epidemiology of Multiple Sclerosis

The Epidemiology of Multiple Sclerosis is measured in two ways. One is incidence and the other is prevalence, but we'll talk about that a little later. But first, what exactly is epidemiology? Is it even worth worrying about? Or is it just an interesting fact to know about MS?

Well, how about we start at the beginning. What does the term epidemiology mean? If you're an average person like me, you don't run across this word very often. So here goes – literally, it means "the study of what is upon the people", it is derived from Greek epi, meaning "upon, among", demos, meaning "people, district", and logos, meaning "study."

Epidemiology of Multiple Sclerosis:
What It Means for You

If you’ve ever wondered why you out of everyone you know developed MS—or why someone you love has it—you’re not alone. The epidemiology of multiple sclerosis is a fascinating field that looks at who gets MS, where they live, when they were born, and even what time of year they were born.

While it may not change your diagnosis, understanding patterns and risk factors can help make sense of the “Why me?” question that so many people ask.

So, let’s break it down in a way that’s easy to understand—without all the scientific jargon.

What Is Epidemiology?

Epidemiology is basically the study of diseases—who gets them, where they occur, and what factors might contribute to their development.

As we mentioned earlier, it’s measured in two ways:

• Incidence – The number of new cases of MS diagnosed in a specific time period.
• Prevalence – The total number of people living with MS at any given time.

Epidemiologists use this data to track trends, identify risk factors, and help doctors understand who is most likely to develop MS.

Who Is Most Likely to Develop MS?

MS doesn’t randomly affect people—it follows certain patterns. Here are some of the biggest risk factors:

1. Age

MS is most commonly diagnosed between ages 20 and 40. While it can occur in children as young as 5 or older adults, it’s much less common at those ages.

2. Gender

Women are two to three times more likely to develop MS than men. Scientists believe hormones may play a role in this difference.

3. Ethnicity

Certain ethnic groups have higher or lower rates of MS. For example:

• Northern European ancestry – Higher risk
• African, Asian, and Indigenous populations – Lower risk

However, African Americans have higher MS rates than Black populations in other countries, possibly due to genetic mixing and environmental factors.

Does Where You Live Matter?

Yes! MS is more common in certain parts of the world—especially in colder climates.

1. Latitude and MS Risk

The farther you live from the equator, the higher your risk of developing MS.

South America = Lower Risk

For example:

• Canada, Scandinavia, and Northern Europe have high MS rates.
• Asia, Africa, and South America have lower MS rates.

Scientists believe this is linked to sunlight exposure and vitamin D levels. Since vitamin D plays a role in immune system regulation, lower levels may increase MS risk.

2. Migration and MS Risk

If you move to a high-MS region before age 15, your risk matches the local population. But if you move after age 15, your risk stays the same as your country of origin.

This suggests that early exposure to environmental factors—like sunlight, diet, and infections—may influence MS risk later in life.

Does the Time of Year You’re Born Matter?

Believe it or not, the season of your birth may play a role in whether or not you develop MS.

Studies show that people born in May have a higher risk, while those born in November have a lower risk.

Why? It likely comes down to vitamin D exposure during pregnancy.

• Babies born in spring may have less vitamin D in the womb (since their mothers were pregnant during winter).
• Babies born in fall may have higher vitamin D levels (since their mothers were pregnant during summer).

This supports the idea that vitamin D deficiency could be a major factor in MS development.

What Does This Mean for You?

If you already have MS, knowing these patterns won’t change your diagnosis—but it can help researchers better understand the disease and work toward prevention and treatment.

If you’re concerned about MS risk, maintaining healthy vitamin D levels through sun exposure, diet, or supplements may be beneficial—though more research is needed to confirm its role in MS prevention. And if you are pregnant, especially during the winter, make sure you are getting enough for your growing child.

The bottom line? MS is influenced by multiple factors—including genetics, environment, and vitamin D levels—but researchers are still working to fully understand the disease. While we don’t have all the answers yet, studies like these bring us closer to better treatments and possibly even a way to prevent it in the future.

If you are more scientifically inclined, here is an article on the PubMed website about the epidemiology of multiple sclerosis. (Link will open in a new window).

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