If anyone is interested, Marshall's explanation of why D levels are low in the chronically ill is as follows: "As the hormone/secosteroid rises above a normal
range, it down-regulates, via the PXR Nuclear Receptor, the amount
of vitamin D converted into 25-D [19]." (Here's the paper: http://mpkb.org/home/publications/al...y_reviews_2009). And the reference is to this piece: http://mpkb.org/home/publications/ma...bioessays_2008.

Some of what he says is right, some of the plausible, and some of it a stretch with at best computer simulations to back it. I usually say beware of complete theories and protocols (or systems) that claim to have figured everything out, but there are interesting and potentially challenging parts to it, even if it doesn't completely stand (and it doesn't as a whole).