Vitamin D supplements and multiple sclerosis: what you need to know

Vitamin D plays a crucial role in MS, and research continues to highlight its impact on disease progression and overall health. Here’s what the latest evidence tells us:

• Higher vitamin D levels at diagnosis are linked to slower disease progression and fewer symptoms.
• Maintaining good vitamin D levels is associated with a lower risk of new brain lesions.
• Low vitamin D levels are associated with a higher risk of relapses, greater disability, and more disease activity.
• Extremely low vitamin D levels (below 50 nmol/L) may double the risk of developing MS.

Maintaining healthy vitamin D levels is essential for people with MS, and experts widely agree on its importance.

In many parts of the world, sunlight is too scarce, or UVB levels are too low to produce enough vitamin D naturally, making supplementation necessary. In fact, an estimated one billion people worldwide are vitamin D deficient. Standard recommended daily intakes (RDIs) don’t account for the specific needs of people with MS, who often require higher doses to reach and maintain adequate levels.

Overcoming MS recommends testing your vitamin D levels as soon as possible after diagnosis. This can be done through a general practitioner or an online testing kit.

If levels are very low, a one-off megadose of vitamin D3 (eg, 600,000 units under medical supervision) may be used to quickly restore levels, followed by regular daily supplementation.

General recommendations:

• A healthy vitamin D level is thought to be between 100–150 nmol/L.
• There is no single ‘good for everyone’ dose, but common recommendations include:
  • 4,000 units per day – a common amount recommended by UK neurologists.
  • 6,000–10,000 units per day – may be needed to maintain optimal levels.

It’s always best to work with your doctor to test your vitamin D levels regularly and find the right dose for you.

If testing your vitamin D levels isn’t possible right now, you can still take steps to maintain healthy levels by taking a moderate daily dose and maximising safe sun exposure. Some healthcare providers, research studies, or public health initiatives offer free or discounted vitamin D testing. It’s worth checking with your GP, healthcare provider, local MS society, or pharmacy to see if any options are available.

Research has found that taking up to 10,400 units per day is safe, and even much higher doses—such as 100,000 units every two weeks—can be used safely under medical supervision.

Serious side effects are rare but taking excessive doses over a long period can lead to high calcium levels in the blood (hypercalcaemia). This is usually only seen in extreme cases, such as people taking 130,000 units per day for 20 months, which is far beyond any recommended dosage.

To stay safe, monitor your vitamin D levels regularly and consult a healthcare professional before taking very high doses.

Research into vitamin D and MS is complex, and randomised controlled trials (RCTs) have not yet definitively proven that supplementation leads to better outcomes. Adding to the complexity, some studies show conflicting results—for example, while some suggest that higher vitamin D levels are linked to reduced relapse rates, others have not found a clear effect.

These differing findings highlight the nuanced role of vitamin D in MS. It’s also important to consider that different types of studies have their own strengths and limitations, which is why we review multiple sources of evidence when making our recommendations.

More research is still needed to fully understand vitamin D’s potential role in MS management.

Ongoing research includes studies on:

• The impact of geography and latitude.
• Epidemiological and population studies.
• Randomised controlled trials.