Vitamin D deficiency and supplementation are linked to multiple sclerosis and disease prognosis

Patients with multiple sclerosis have lower blood levels of vitamin D compared with healthy individuals. In addition, higher-dose vitamin D supplementation is associated with a reduced risk of relapses, which are new neurological symptoms or flare-ups of previous symptoms, according to a meta-analysis published in Frontiers in Immunology. Strong summer sunlight is the primary source of vitamin D, and multiple sclerosis is more common in Nordic countries and populations with limited sun exposure. There is also no guarantee that the official recommendations for vitamin D supplementation are sufficient to optimize blood levels.

Multiple sclerosis is a chronic autoimmune disease of the central nervous system that primarily affects young adults. Multiple sclerosis (MS) is the general term for the disease, which is divided into three types: relapsing-remitting multiple sclerosis, primary progressive multiple sclerosis, and secondary progressive multiple sclerosis, which differ in several ways.
Overall, multiple sclerosis is characterized by inflammatory processes that destroy the insulating, cholesterol-rich myelin surrounding the long fibers of nerve cells. This disrupts nerve impulses and may lead to fatigue, sensory disturbances, and symptoms throughout the body depending on which nerve cells are affected. Multiple sclerosis is also characterized by relapses, which are new symptoms or flare-ups of previous symptoms.
Multiple sclerosis affects more women than men. The disease can also vary greatly, as some patients experience a more aggressive progression with worsening disability and reduced quality of life.
Although it is already well established that vitamin D plays a role in regulating the inflammatory processes involved in multiple sclerosis, uncertainty has remained regarding whether blood vitamin D levels and vitamin D supplementation can help prevent new relapses and disease progression. The purpose of the new meta-analysis was therefore to investigate this in greater detail, including the various subtypes of multiple sclerosis.

• Relapsing-remitting multiple sclerosis (RRMS), the most common form, occurs in attacks with acute symptoms that subsequently subside or disappear completely for a period. Symptoms include sensory disturbances, vision problems, dizziness, or reduced muscle strength
• Primary progressive multiple sclerosis (PPMS) is characterized by a slow and steady worsening of neurological symptoms without relapses from the onset of the disease. The most common symptoms are fatigue, weak and stiff muscles, difficulty walking, and balance problems
• Secondary progressive multiple sclerosis (SPMS) is a stage of relapsing-remitting multiple sclerosis in which gradual functional decline continues independently of relapses.

Blood vitamin D levels and higher-dose supplementation are crucial

The researchers collected a number of relevant studies published before November 2025 from databases such as PubMed, Cochrane Library, and Web of Science. Of these, 40 studies examined the relationship between blood vitamin D levels and multiple sclerosis. Another 22 studies investigated the effects of different doses of vitamin D supplementation on multiple sclerosis, with treatment durations ranging from 24 to 192 weeks. The meta-analysis revealed the following:

• Higher blood levels of vitamin D were associated with a lower risk of developing multiple sclerosis
• Blood vitamin D levels were significantly lower in patients with multiple sclerosis compared with healthy control groups
• Analyses of multiple sclerosis subtypes showed that patients with secondary progressive multiple sclerosis had significantly lower blood vitamin D levels than patients with relapsing-remitting multiple sclerosis
• Patients with relapsing-remitting multiple sclerosis had significantly lower blood vitamin D levels during relapse periods compared with periods without relapses
• Studies on vitamin D supplementation revealed that lower doses (10–25 micrograms per day) had no significant effect on the number of relapses. It may also be noted that the official daily recommendations for vitamin D supplementation are even lower (5–20 micrograms)
• Only higher-dose vitamin D supplementation (70–510 micrograms per day) significantly reduced the number of relapses

The researchers therefore conclude that patients with multiple sclerosis have significantly lower blood vitamin D levels compared with healthy control groups. There is thus an inverse relationship between blood vitamin D levels and the risk of developing multiple sclerosis. In addition, higher-dose vitamin D supplementation is associated with a lower risk of developing relapsing-remitting multiple sclerosis and with fewer relapses during the course of the disease. The researchers therefore assume that vitamin D’s ability to prevent and alleviate multiple sclerosis is related to the size of the supplemental dose. As shown, several studies used vitamin D doses that were far above the daily upper intake level of 100 micrograms established by European Food Safety Authority. However, these higher doses do not contain more vitamin D than most fair-skinned individuals can produce from sun exposure on a good summer day if most of the body is exposed. Needless to say, sunburns should always be avoided.
In any case, it appears relevant that supplementation should optimize blood vitamin D levels, and for patients with multiple sclerosis, levels in the upper end of the normal range (50–160 nmol/L) may be preferable.

References:

Yanan Li et al. Vitamin D status, supplementation, and multiple sclerosis: a systematic review and meta-analysis. Frontiers in Immunology. 2026

Prince Sebastian et al. Association between Time Spent Outdoors and Risk of Multiple Sclerosis. Neurology, 2021