20-05-2025
Labos: What we know — and don't — about vitamin D and multiple sclerosis
Though I rarely pass up an opportunity to remind people that taking vitamins and supplements is often pointless, the key to science is learning how to be a skeptic without being a cynic. The role of vitamin D in preventing or treating multiple sclerosis demonstrates just how difficult that can be.
Multiple sclerosis is a complex disease. The ultimate cause is unclear though very likely immune-mediated and possibly triggered by pathogens like Epstein-Barr virus. It is nearly twice as common in women compared to men, which suggests genetics play a role. It is also more common in people living in northern latitudes and where lack of sunlight and vitamin D deficiency have been hypothesized as possible contributing factors.
With any such association, it is always hard to tease out if vitamin D deficiency is an independent cause of disease or simply a marker of other underlying issues. With multiple sclerosis, genetic analyses suggested that it might in fact be a direct cause, which is why randomized controlled trials on the issue have been met with such interest.
Recently, the D-Lay MS randomized clinical trial has suggested vitamin D might actually delay the progression of multiple sclerosis. It would be tempting to get excited by the results, but studies do not exist in a vacuum and previous research on this subject has not been very encouraging.
A study in 2012, initially designed to look at bone mineral density, did not find that vitamin D affected relapse rates in MS patients.
Two more studies in 2019 were equally disappointing:
The SOLAR study took 229 patients with relapsing-remitting MS and randomized them to 14,000 units of vitamin per day versus placebo on top of regular interferon therapy. There was no clinical benefit but there was some improvement on the MRI scans of patients who took the high dose vitamin D.
The CHOLINE study similarly randomized 181 patients with relapsing-remitting MS to 100,000 units of vitamin D weekly. It too showed no overall clinical benefit although some improvement in patients who were able to complete the trial.
The 2023 VIDAMS trial tested high dose (5,000 units/day) versus low dose (600 units/day) vitamin D as an add-on to glatiramer instead of interferon in relapsing-remitting MS patients. It was negative.
Shortly thereafter, 2024 saw the publication of a study in 204 patients with clinically isolated syndrome — that is, symptoms consistent with MS but who did not meet the diagnostic criteria. They received either placebo, 1,000, 5,000 or 10,000 units daily, but to no effect.
The recent D-LAY MS trial was in a similar vein testing 303 patients with clinically isolated syndrome within the first 90 days of diagnosis. They received a very high dose of 100,000 units of vitamin D every two weeks. Vitamin D showed a reduction in disease activity from 74 per cent to 60 per cent of patients, but largely because of decreased MRI activity rather than fewer clinical relapses.
Putting this most recent trial in a broader context is hard. The studies have all used different doses in different types of MS patients. Their numbers are small and possibly would not pick up small clinical improvements. Also, while improvements on MRIs are interesting, they are not a substitute for actual clinical and symptomatic improvement.
The evidence base for vitamin D is not as strong as some would have you believe, but there is at least more evidence for multiple sclerosis than for heart disease or cancer.
Given the low cost and lack of serious side-effects, vitamin D could be considered in the absence of any better alternative in someone with a new diagnosis. But we still need far larger trials to confirm a clinically meaningful benefit. Stay tuned.
