I am certain doctors would say that all that happens is that that vit d brings an overactive immune system under control... the same thing said about any number of drugs they hand out.
just in case you are curious, the dendritic cells that vit D targets with its "immunosuppresive activity".. here is a bit about them, still think vit d is harmless?
better think again. get some sun if you need vitamin d, or eat some real food. if that doesn't do it for you, you have a much bigger problem than low vit d blood levels. but, doctors won't tell you that.
could go on all night posting these studies, but, that would be a waste of time. its all here.