This is based on the nitric oxide pathway which has been well researched and has won two scientists the Nobel Prize.
I first heard about M.D. endocrinologist Dr. Joseph Prendergast on a radio show from the San Francisco area called The Vitamin Shelf with host David Stouder. I find them fascinating and have listened to all episodes featuring Dr. Prendergast at least twice. He has prescribed daily doses of fifty thousand IU's of Vitamin D since 1964 (it was prescribed for osteomalacia back then)!
The radio shows describe some of the common protocols that Dr. Prendergast uses with the patients who see him. He often has new patients take fifty thousand IU's daily for thirty to sixty days and then he tests their blood levels. Then they will reduce daily intake to between five and twenty thousand IU's after that to maintain a target blood level of between "100 and 200". I'm pretty sure he's talking about ng/mL although he never does specify. In the March 17, 2009 show he says that if patients remain on a high intake for more than 200 days that their blood levels will peak at that time and then actually begin to decline until about day 365.
David Stouder's radio shows are archived on the internet as freely downloadable mp3 files if you're interested. The first seven listed below feature Dr. Prendergast as a guest and the eighth features perhaps the world's foremost authority on Vitamin D toxicity:
(a) posted to website on May 2, 2007
http://www.thevitaminshelf.net/audio/drjoe2.mp3(b) June 6, 2007
http://www.thevitaminshelf.net/audio/L-Arg-VitD.mp3(c) March 9, 2008
http://www.thehealthwarrior.net/mp3/THW-3-09-08.mp3(d) July 20, 2008
http://www.thevitaminshelf.net/audio/tvs7-17-08se.mp3(e) Nov. 9, 2008
http://www.thehealthwarrior.net/mp3/THW-11-09-08.mp3(f) Feb. 23, 2009
http://www.thevitaminshelf.net/audio/tvs2-18-09a.mp3(g) March 17, 2009
http://www.thehealthwarrior.net/mp3/THW-3-17-09.mp3(h) This Jan. 17, 2009 interview with University of Toronto researcher Rheinhold Vieth is also very good.
http://www.thevitaminshelf.net/audio/tvs12-22-08.mp3Dr. Prendergast's contact info is as follows:
Endocrine Metabolic Medical Center
350 Cambridge Avenue, Suite 250
Palo Alto, CA 94306-1575
Telephone: (650) 566-9810
Fax: (650) 566-9825
email:
office@endocrinemetabolic.comwebsite:
http://www.endocrinemetabolic.com/