The D-Lay MS trial was a phase 3, double-blind, randomized, placebo-controlled trial - this means it was a really well designed study!
It was conducted across 36 MS centres in France.
It was published in one of biggest medical journals, The Journal of the American Medical Association (JAMA), in 2025.
Involved 316 people aged 18–55
recent clinically isolated syndrome (CIS) highly suggestive of MS, including an MRI scan or lumbar puncture (spinal tap features indicating a high likelihood of MS
and had relatively low vitamin-D levels (<100 nmol/L)
and they had not yet started a disease-modifying therapy
For 2 years, the participants received either:
-100,000IU Vitamin D3 (cholecalciferol) every 2 weeks, equivalent to roughly 7,100 IU/day
-or placebo
Disease activity occurred in:
- 60.3% of the vitamin-D group
- 74.1% of the placebo group
Vitamin D reduced:
- MRI disease activity
- new lesions
- Gadolinium-enhancing lesions
But...vitamin D had no benefit for:
- relapse
- disability (EDSS)
- fatigue
- quality of life
- depression or anxiety
So vitamin D had some minor benefit in the D-Lay study but it is important to note this study only looked at a certain profile of people.
The D-Lay study does not tell us if vitamin D is beneficial for:
- anyone with MS for a year more
- has progressive MS
- is already taking an MS DMT
- has a normal or high vitamin D blood level
- is younger than 18
- is older than 55
- has substantial established disability
The D-Lay, consistent with the existing vitamin D research in multiple sclerosis, suggests minor benefit, if any, of vitamin D supplementation
MS is a horrible disease and for me as a patient but also but clinician and researcher, a possible minor benefit is better than no benefit so I take and recommend vitamin D
Just don't expect miracles...
Yours in health,
Dr. Conor Kerley
living (well) with multiple sclerosis since 2002, aged 15
Comments