When I saw that natural vitamin D3 was supposed to be dangerous, but there was a drug which was better and safer, there was a faint odor of day old fish. Upon checking it became riper still.
The link to the article goes to a website created by Amy Proal, Bioavailability.com, and the article is one she wrote herself, in which she quotes "biomedical researcher" Trevor Marshall telling how a drug he happens to push as part of his Marshall Protocol is more effective than the natural vitamin D3 we get from the sun, diet and supplementation, and that too much natural D3 can be dangerous and turn off the immune system.
A quick Google reveals that Amy Proal has written lots of articles about Marshall, who is also referred to as Dr. Marshall. She has also recorded live interviews with him and has appeared with him at lectures. Ms. Proal has a page on her website about the Marshall Protocol and claims to have been cured of Chronic Fatigue Syndrome by his protocol.
Maybe Ms. Proal is on the up and up, but I am not so sure. I am even more unsure about Dr. Marshall the biomedical researcher. It turns out that he has no medical background. In fact, Marshall obtained a Bachelor of Electrical Engineering from the University of Adelaide in 1974. In 1978, he obtained a Master of Engineering (RF Digital Electronics). He holds a Ph.D. qualification issued by the University of Western Australia, Department of Electrical and Electronic Engineering, so technically he could be called "Doctor".
While he has little background in medicine, he does have a rather shady background that includes subterfuge, false statements and creating his own on-line journal to pubish his papers in:
http://sci.tech-archive.net/Archive/sci.med.diseases.lyme/2005-08/msg01695.html (you may have to cut and paste the link, my FCK editor is farkled tonight)