Vitamins and minerals are listed on nearly every nutrition label, including those of foods and drinks that claim to be fortified with nutrients. You may have heard that vitamin D, a commonly fortified vitamin, is good for calcium absorption and bone health. But what is the role of vitamin D in multiple sclerosis (MS)?

Research suggests that vitamin D may play a bigger role in MS risk and symptoms than previously thought. This article explores the connection between vitamin D levels and MS, but it’s important to note that a link doesn’t mean one causes the other. More research is needed to fully understand vitamin D’s impact on MS.

Does Vitamin D Help With MS?

Research consistently links low vitamin D levels to MS and other autoimmune diseases. In addition to supporting bone and muscle health, vitamin D helps regulate the immune system and immune cells (like T cells and B cells), which are abnormal in MS.

Some studies suggest that vitamin D has a protective effect. For example, researchers have found that people with higher levels of vitamin D (based on diet or blood tests) had a 40 percent to 62 percent lower risk of developing MS compared to people with lower levels. Additionally, in people with clinically isolated syndrome (early symptoms that suggest MS), low vitamin D levels were linked to more severe progression of MS.

The connection between low vitamin D levels and MS may also explain why MS is more common in areas farther from the equator, where there’s less sunshine to help the skin produce vitamin D. However, newer research suggests that this protective effect may not apply equally to all groups. Scientists believe that genes and environmental factors may interact in complex ways to influence MS risk.

Vitamin D Supplementation

Just because a deficiency of a nutrient, like vitamin D, is strongly linked to a disease doesn’t mean that taking more of it will help people already experiencing symptoms. Scientists must first show that supplementation provides benefits before doctors can recommend it for a specific disease like MS.

Some studies suggest that high-dose vitamin D intake may help reduce disease progression, disease activity, and relapse rates in people with MS, but other studies don’t agree. A recent review of research from 2000 to 2024 found that while vitamin D may help lower relapse rates, there isn’t strong evidence that it improves quality of life or slows disability with MS. Although vitamin D supplementation may help some people, it doesn’t replace disease-modifying therapies for MS.

What Is Vitamin D and How Is It Made?

Vitamin D enters the body in two main forms — vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D2 is mostly human-made and added to certain foods, whereas vitamin D3 comes mainly from sunlight exposure. When sunlight hits the skin, skin cells use its energy to make vitamin D3.

Both forms of vitamin D travel to the liver, where they’re converted into 25-hydroxyvitamin D, abbreviated as 25(OH)D, a precursor of active vitamin D. Next, the kidneys process 25(OH)D into its active final form, calcitriol. This active vitamin D helps support bone growth, maintain calcium levels to prevent osteoporosis (brittle bone disease), and strengthen the immune system.

How Can Vitamin D Levels Be Raised?

The best way to maintain healthy vitamin D levels is through a balanced diet that includes vitamin D-rich foods such as fatty fish, eggs, and fortified dairy products, along with safe sun exposure. However, getting enough vitamin D from food and sunlight alone can be difficult, especially for those with limited sun exposure or dietary restrictions.

Although vitamin D supplements are available over the counter, it’s important to talk with your doctor before starting them. Your doctor can check your vitamin D levels, assess your needs, and determine the right dose and type of supplement, if necessary.

More than 14,000 MyMSTeam members report taking vitamin D supplements, which come in vitamin D2, vitamin D3, or a combination of both. Even though they’re available over the counter, these supplements should be used only after consulting a doctor.

How Much Vitamin D Should a Person With MS Take a Day?

Various professional organizations, such as the Institute of Medicine and the Endocrine Society, provide guidance on optimal vitamin D levels and intake. For people with MS who have a vitamin D deficiency, doctors typically recommend maintaining blood levels between 40 and 60 nanograms per milliliter (ng/mL). However, this is a general guideline, and the ideal level may vary for each person. It’s important to discuss your specific target range with your doctor.

Depending on vitamin D levels in the blood, common supplementation options may include:

• High-dose vitamin D2 — Typically 50,000 international units (IU) per week
• Vitamin D3 — Usually taken at 1,000 to 2,000 IU per day

The right dose of vitamin D varies widely based on individual factors, such as baseline vitamin D levels, other health conditions, and medications. Only a doctor can determine the correct dose for you. Before starting any supplements, talk to your doctor to ensure safety and effectiveness and to get the proper dose and frequency for your specific needs.

Can You Take Too Much Vitamin D?

In short, yes. Having too little vitamin D can be a problem, but too much can also be harmful. Vitamin D toxicity occurs when levels are too high, potentially worsening MS symptoms and causing complications such as encephalomyelitis (inflammation of the brain and spinal cord), as seen in some animal studies. It’s important to remember that more is not always better when it comes to vitamins. Excessive vitamin D intake can lead to serious side effects, including hypercalcemia. Also, there’s no evidence that extremely high doses of vitamin D provide any extra benefits for people with MS.

Vitamin D toxicity can cause hypercalcemia (dangerously high calcium levels), a condition that may lead to kidney problems, heart issues, and other complications. While 10,000 IU per day is often cited as a general threshold, toxicity can occur at lower doses in some individuals. It’s crucial to know the signs and symptoms and discuss any concerns with your doctor before taking high doses of vitamin D.

Signs and Symptoms of Excess Vitamin D

Vitamin D toxicity, also known as hypervitaminosis D, can occur in people who take doses above 10,000 IU per day. Signs and symptoms of vitamin D toxicity may include:

• Constipation
• Dehydration
• Vomiting
• Irritability or altered mental status
• Excess thirst
• Frequent urination
• Severe bone pain
• Kidney problems, such as kidney stones
• Heart problems

Does Vitamin D Make Your Urine Smell?

Some members of MyMSTeam have wondered whether vitamin D supplements can cause urine to smell — and if so, whether it indicates that their vitamin D levels are too high.

Although several vitamins, especially vitamin B, can affect urine odor, vitamin D itself usually doesn’t cause noticeable changes. However, if you’re taking vitamin D supplements and notice a strong smell in your urine, it could indicate:

• Dehydration, which can be a side effect of excess vitamin D
• A urinary tract infection
• Other underlying health conditions

If you’re worried you may have taken too much vitamin D, contact your doctor right away. In some cases, vitamin D toxicity can cause permanent kidney damage.

Ask Your Doctor About Your Vitamin D Levels

It’s essential to consult your doctor before starting any vitamin D supplements. Although vitamin D is available over the counter, it carries potential risks, especially for those with preexisting medical conditions. Your doctor can evaluate your vitamin D levels, consider your overall health, and determine whether supplementation is appropriate and at what dosage. This is particularly important for people with kidney problems, as their bodies may process vitamin D differently.

Your doctor or other healthcare professional, such as a clinical pharmacist or dietitian, can also help determine the dosage of vitamin D based on your specific health conditions. For example, people with renal insufficiency (a type of kidney problem) may need supplements with different vitamin D concentrations to achieve the same effect.

Vitamin D supplements may interact with other drugs, such as:

• Atorvastatin (Lipitor) and certain other cholesterol drugs
• Digoxin (Lanoxin), a heart medication
• High blood pressure medications
• Laxatives
• Steroids

These interactions can either reduce the effectiveness of the other medication or increase the risk of side effects. It’s important to tell your doctor about all the medications you take, including over-the-counter drugs and supplements, before starting vitamin D supplementation. If you’re taking other medications, speak with your doctor to determine whether vitamin D supplements are appropriate for you and what a safe dosage will be.

Testing Vitamin D Levels

Your doctor may perform blood tests to track your vitamin D status and find out if your vitamin D levels are normal. One MyMSTeam member described having their 25(OH)D level checked twice a year: “Depending on the test result, my doctor would adjust the supplementation level for the next six months.”

Vitamin D test results may be reported in nanomoles per liter (nmol/L) or nanograms per milliliter, so it’s important to know which units your lab uses. While 30 nmol/L (12 ng/mL) is often used as a cutoff for deficiency, and 50 nmol/L (20 ng/mL) is generally considered sufficient, these are only guidelines. Your doctor will interpret your vitamin D levels based on your overall health and other risk factors. If your levels are low, your doctor may recommend vitamin D supplements.

Talk With Others Who Understand

On MyMSTeam, the social network for people with multiple sclerosis and their loved ones, more than 218,000 members come together to ask questions, give advice, and share their stories with others who understand life with multiple sclerosis.

Do you have low vitamin D levels? Has improving vitamin D levels improved your symptoms? Share your experience in the comments below, or start a conversation by posting on your Activities page.