Vitamin D and MS relapses: new real-world study suggests higher blood levels are linked to fewer relapses

Vitamin D is one of the most common supplements people with MS ask about – and also one of the most confusing. Some studies suggest it may help reduce MS activity, while others find no clear benefit.  That can be frustrating, especially if you’ve been told by your MS team that vitamin D “doesn’t make any difference”. 

A new large “real-world” study adds an important perspective: instead of looking at a fixed supplement dose, it looked at people’s actual vitamin D blood levels over time – and how those levels related to relapses. The findings help explain why vitamin D research findings can appear inconsistent, and what a more personalised approach might look like.

This study adds further evidence that it is vitamin D blood levels, rather than supplement dose alone, that matter when considering MS relapse risk. This helps to explain why some trials show benefits while others do not.”
Dr Jonathan White, Medical Advisor, Overcoming MS

The evidence: what this new study found

Researchers analysed 10 years of data from the Czech national MS registry (ReMuS), including 1,861 adults with MS. They focused on 25(OH)D, the standard blood test used to measure vitamin D status, which was typically checked twice a year as part of routine care. This was a real-world study using routine clinical data. Vitamin D levels were monitored regularly, and any supplementation was managed by treating clinicians as part of usual care, rather than being directed by the study.

Although the registry includes people with different types of MS, the analysis focused on relapses. This means the findings mainly apply to people with relapsing MS.

Key findings:

• 25(OH)D levels were associated with a lower risk of relapse.
• For every 10 nmol/L increase in 25(OH)D, relapse risk was reduced by around 6.7%.
• In longer follow-up analysis, people with average 25(OH)D levels above 100 nmol/L had fewer relapses than those below 75 nmol/L.
• The authors reported no adverse effects observed during follow-up monitoring.

This was an observational study. That means it can’t prove vitamin D caused fewer relapses – but it does show a strong association in a large, long-term dataset.

What this means for you (and what to say if you’re told “there’s no benefit”)

This study supports a more practical way to think about vitamin D:

The most useful question may not be “should I take vitamin D?” but “what vitamin D blood level am I aiming for, and am I actually reaching it?”

That framing can be helpful when teams are cautious about the supplementation evidence. Many are comfortable with:

• testing 25(OH)D
• correcting deficiency
• monitoring levels over time as part of overall health

It can also explain why some people see benefits while others don’t: outcomes may depend on baseline levels, achieved blood levels, and individual factors – not just whether someone took a supplement.

Practical steps: vitamin D and MS

This study supports Overcoming MS’s advice that if you’re considering vitamin D – or already supplementing – a personalised, monitored approach is best.

Overcoming MS recommends that people with MS supplement with between 4,000 and 10,000 IU of vitamin D per day, depending on individual needs. Because people respond differently, the most helpful approach is to combine supplementation with testing and review.

You may wish to:

• Ask for a blood test to check your vitamin D level (25-hydroxyvitamin D or 25(OH)D).
• Work with a healthcare practitioner to agree a supplementation dose that suits you.
• Re-test your levels after a few months, particularly if you change your dose.
• Take into account factors such as sun exposure, season and where you live, which all affect how much vitamin D your body produces naturally.
• Avoid assuming “more is always better”. Research suggests that once vitamin D levels reach an optimal range, higher doses don’t appear to provide additional benefit. Monitoring levels helps ensure supplementation is appropriate for you.