The immune system must be able to discriminate between self and non-self. That is, the immune system must be able to recognize the difference between foreign invaders and your own cells. When self/non-self discrimination fails, the immune system destroys self (cells and tissues of the body) and causes autoimmune diseases, diseases like multiple sclerosis, lupus or type 1 diabetes.
Regulatory T cells (Tregs) are a form of immune cell, which help tame the immune system, maintaining self-tolerance. Tregs actively suppress activation of the immune system and prevent pathological self-reactivity, i.e. autoimmune disease. Mouse models have suggested that increasing Treg percentages can treat autoimmune disease.
The severe autoimmune syndrome that results from a genetic deficiency of Tregs, the IPEX syndrome, brings insight to the critical role Tregs play within the immune system. The IPEX syndrome is characterized by the development of overwhelming systemic autoimmunity in infancy, resulting in the commonly observed triad of watery diarrhea, severe eczema and type 1 diabetes.
I have written about Tregs before, but until recently, no one has researched the effect of vitamin D supplementation on Treg percentages in a healthy population.
Dr. Barbara Priedl, working under senior author Professor Thomas Pieber, both of the University of Graz in Austria, conducted a randomized controlled trial of vitamin D supplementation in 60 healthy adults to see if Treg percentages changed, hoping for a clue as to how vitamin D might treat autoimmune disorders.
Prietl B, et al. High-dose cholecalciferol supplementation significantly increases peripheral CD4+ Tregs in healthy adults without negatively affecting the frequency of other immune cells. Eur J Nutr. 2013 Sep 3.
They gave 30 patients 140,000 IU/month (equivalent to about 4,500 IU/day) of D3 for three months, then, at month four, they assessed the two groups for changes in Treg percentages, comparing them to the placebo group.
First, they found that baseline 25(OH)D levels correlated with percentages of Tregs in peripheral blood. Second, they found “very high dose” D3 supplementation only increased 25(OH)D levels to natural ranges, about 55 ng/ml. Third, they found Treg percentages in peripheral blood fell in the placebo group (the study was conducted between November and March), but increased from 4.89% at baseline to 6.35 % at 3 months (P<.001) in the treatment group.
So at least one mechanism of action of how vitamin D may prevent and even treat autoimmune disorders is now firmly established. Vitamin D is important for autoimmune disorders because it increases Tregs.