Vitamin D Deficiency Linked To Increased Autoimmune Risk

While vitamin C is arguably the best-known nutrient for immune defense, vitamin D has a lot to do with immunity, too. This fat-soluble essential vitamin supports a multitude of cellular functions that support the body’s immune response1—including protecting against pathogens and scavenging free radicals.

Autoimmune disease triggers the immune system to target its own body, rather than the infection itself. It also makes people with autoimmune diseases more susceptible to infections, viruses, and illnesses.

“Vitamin D pathways impact autoimmune disease pathologies through [vitamin D’s] role as an immunomodulator,” family medicine physician Laura Purdy, M.D. explains. “Vitamin D has been shown to regulate the immune system by promoting the differentiation of regulatory T cells3, which help prevent autoimmunity by suppressing the activity of other immune cells that attack the body’s own tissues.”

She adds: “Additionally, vitamin D can reduce the production of pro-inflammatory cytokines4, which are molecules that promote inflammation and contribute to the development and progression of autoimmune diseases.”

“Rheumatoid arthritis is caused by inflammation that leads to tissue damage in the joints,” emergency medicine physician and medical editor at GoodRx, Katie Golden, M.D., explains. “Research suggests that vitamin D deficiency may contribute to the development of rheumatoid arthritis5, as well as correlate with disease severity.”

According to a 2016 review from Clinical and Experimental Rheumatology, approximately 55% of RA patients6 are deficient in vitamin D. Additionally, research shows an inverse relationship between RA and vitamin D, in that activity increases when D status decreases. 

In a 2023 Arthritis Research & Therapy study, 42% of systemic lupus erythematosus (SLE) patients were found to also have VDD.

In a 2017 Neurology and Therapy review, lower vitamin D levels were found to be strongly associated with the development of new T2 lesions7—i.e., damage to the outer layer of neurons caused by MS activity. 

Additionally, the review found that each 10 ng/ml increase of 25(OH)D serum levels lowered both the risk of new T2 lesions in MS patients (by 15%) and the risk of enhancing existing lesions (by 32%).

“Research has suggested that vitamin D deficiency increases someone’s risk for developing multiple sclerosis,” Golden explains. On the other hand, achieving optimal vitamin D status has also been shown to reduce the likelihood of developing MS by 62%8.

Research has shown that vitamin D helps modulate blood sugar and promote healthy insulin levels9. This could explain why diabetes has also been linked to vitamin D deficiency. 

“[Biological] sex can affect the relationship between autoimmune disease risk and vitamin D, as studies have shown that women are more likely to develop autoimmune diseases than men, and also tend to have lower levels of vitamin D,” Purdy explains. “This suggests that there may be a link between sex hormones and vitamin D metabolism, which could influence the development and progression of autoimmune diseases.”

While food rich in vitamin D (e.g., egg yolk, fatty fish, liver, and grass-fed butter, according to Bourgeois) and sun exposure (it’s called the “sunshine vitamin,” after all) do increase vitamin D levels, neither are reliable sources of vitamin D for most people—especially in the long term.