A bit more digging:

This long review might be worth a read; http://www.ncbi.nlm.nih.gov/pmc/arti...MC4078458/#B50.

Nothing crystal-clear has emerged but it seems that:

(1) There is evidence that Vitamin D (and by inference, genes which are under the control of the VDR) may be protective against multiple sclerosis.

(2) There is similar evidence which is suggestive of protective effects in rheumatoid arthritis and Inflammatory Bowel Disease.

(3) Low levels of Vitamin D in childhood may be a risk factor for Type 1 diabetes.

(4) There is complex evidence that Vitamin D can down-regulate the production of pro-inflammatory proteins.

(5) There is conflicting evidence about the effects of Vitamin D on asthma.