Vitamin D and Autoimmunity

Vitamin D deficiency has been implicated in several autoimmune disease, including systemic lupus erythematosus (SLE), type 1 diabetes, rheumatoid arthritis, inflammatory bowel disease and multiple sclerosis (MS). Munger and colleges tested the vitamin D levels in the serum samples collected in the US Army repository. They found that "high circulating levels of vitamin D are associated with a lower risk of multiple sclerosis". When they investigated cause-and-effect, they found:

“Average 25- hydroxyvitamin D levels among individuals who developed MS were stable during the years preceding symptom onset (P=.42 for trend) but significantly decreased after onset of symptoms (P=.002). Mean 25-hydroxyvitamin D levels were 71.8 nmol/L more than 6 years before symptom onset (51 cases),…”

Surprisingly, they continue:

“These results argue against the possibility that the low preclinical 25-hydroxyvitamin D levels among individuals with MS are a consequence rather than a cause of the disease,..."

This finding seems to suggest that MS causes the decrease in vitamin D levels, not vice versa. Also, the average levels preceding the development of symptoms (71.8 nmol/L) is actually protective (figure). This seems inconsistent with a conclusion that low vitamin D contributes to MS (a conclusion they do not draw explicitly, instead stating they have established an “association”).