Vitamin D supplementation improves cytokine profiles in patients with congestive heart failure
This study found that Vit D was able to lower the levels of a compound called IL-10. While IL-10 is not the queen of all inflammatory mediators, it is very high up on the hierarchy. This means that IL-10 turns on a bunch of other enzymes involved in inflammation. So, lower levels of IL-10 equals less inflammation.
While this study was done on congestive heart failure patients, it has ramifications for every other type of autoimmune disease as well. Also, the levels used, 50 micrograms (about 2,000 IU), is definitely a good dosage.