Vitamin D and the immune system, including autoimmunity
What it found
Vitamin D helps immune cells work and may lower the risk of autoimmune diseases like type 1 diabetes and multiple sclerosis.
The evidence comes from lab tests, animals and some studies in people.
What they found
Studies in people
Infections and vitamin D
In people, low vitamin D levels have been linked to more respiratory infections. A trial in severely deficient Mongolian children found fewer acute respiratory infections over 3 months with fortified milk. But a trial in healthy adults with good vitamin D levels found no reduction in upper respiratory infections with a monthly dose of 100,000 IU vitamin D3.
Type 1 diabetes risk
A study found that children who took vitamin D supplements in their first year of life had a 33% lower risk of developing type 1 diabetes. A meta-analysis of four large studies also found a lower risk in infants who received supplements.
Type 1 diabetes treatment
Trials testing vitamin D in people who already have type 1 diabetes have shown mixed results. One trial using 2000 IU of cholecalciferol for 18 months in 38 patients found less loss of beta-cell function.
Multiple sclerosis
Some studies found that vitamin D supplementation reduced the risk of developing multiple sclerosis or helped as an add-on therapy. But recent placebo-controlled trials found no benefit on MRI brain lesions or relapse rates.
Animal and lab studies
Immune cells use vitamin D
Many immune cells, such as T cells, B cells and monocytes, have the tools to take in vitamin D and turn it into its active form. This lets vitamin D change how these cells behave.
Calcitriol and immune balance
In lab tests, the active form of vitamin D, calcitriol, pushes immune cells toward a more tolerant state. It lowers inflammatory signals and raises some anti-inflammatory ones.
What the authors conclude
“However, taking all current evidence together, vitamin D emerges as a promising and relatively safe nutrient for new strategies in the prevention and adjunctive treatment of diseases caused by impaired immune-homeostasis.”
Also in their conclusions
- They say that vitamin D interacts with both the innate and adaptive immune system and that insufficient levels may lead to immune dysregulation.
- They note that a recent systematic review of 219 studies concluded that vitamin D seems to play a beneficial role in preventing autoimmunity, but that there is still a lack of randomized controlled trials.
- They advise that more and larger clinical trials are needed to determine how vitamin D supplementation affects different diseases and to find the best dose and form.
How it was done
Scientists wanted to understand how vitamin D affects the immune system beyond its known role in bone health, and whether it might help prevent or treat autoimmune diseases.
The authors reviewed published studies on vitamin D and immune cells, including lab tests, animal experiments and human trials. They focused on autoimmune diseases, especially type 1 diabetes and multiple sclerosis.
What it can’t tell you
- Many of the findings come from lab tests or animal studies, so they cannot show what happens in people.
- Some human studies are observational, so they can show a link but not prove that vitamin D causes the effect.
- The trials in people often used different doses, forms and durations, making it hard to compare results.
Who paid
- Authors work at
- Medical University of Graz, Austria
The paper
- Title
- Vitamin D and immune function
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Cite
- Prietl B, Treiber G, Pieber TR, Amrein K (2013). Vitamin D and immune function. Nutrients. doi:10.3390/nu5072502Free full textPubMed 23857223DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error