How important is Vitamin D for autoimmune disease?

It's hard to overemphasize the importance. Consider this paper published in Nature Reviews Rheumatology in which the authors assert that the...

"...immunoregulatory and anti-inflammatory properties" of vitamin D can be used for the "control of autoimmune diseases."

They note that...

"...Epidemiological evidence indicates a significant association between vitamin D deficiency and an increased incidence of several autoimmune diseases,"

Which include...

"a variety...from rheumatoid arthritis to systemic lupus erythematosus, and possibly also multiple sclerosis, type 1 diabetes, inflammatory bowel diseases, and autoimmune prostatitis."

(Extra highlight for autoimmune prostatitis because very few are aware how common this is.) Of great practical importance is their observation that...

"The net effect of the vitamin D system on the immune response is an enhancement of innate immunity coupled with multifaceted regulation of adaptive immunity."

We are awash in studies on vitamin D, here's one more for good measure. This paper, recently published in the journal Psychoneuroendocrinology, focuses on its use in the treatment of autoimmune disease that attacks the brain and nervous system. The authors begin by noting that...

"It has been known for more than 20 years that vitamin D exerts marked effects on immune and neural cells...it has been shown that diminished levels of vitamin D...is a risk factor for various brain diseases."

They further state that...

"...vitamin D has been found to be a strong candidate risk-modifying factor for Multiple Sclerosis (MS)..."

And proceed to..

"...assess how vitamin D imbalance may lay the foundation for a range of adult disorders, including brain pathologies (Parkinson's disease, epilepsy, depression) and immune-mediated disorders (rheumatoid arthritis, type I diabetes mellitus, systemic lupus erythematosus or inflammatory bowel diseases)."

These are some of the reasons why I always screen for vitamin D sufficiency.