[enentique]

Thanks to Dr. Payne for submitting this.

http://www.sciencedaily.com/releases...0520114657.htm


There is a similar story in the Pulmonary forum.

[nilliraq]

I am currently taking 5000 iu of vitamin D3 and alternate between D2 and D3. Will these over the counter vitamins do the same thing in the body?

[alexosnasos2]

Since Dr. Payne first gave us the info on Vitamin D, I sent your question to him. His very thorough reply is below. Thank you Dr. Payne.




In-a-word, yes they will. Of course, for a very long it was though that D3 was superior to D2 when it comes to maintaining blood levels of 25-hydroxyvitamin D (The biologically active form of vitamin D). This was laid to rest when scientist from Boston University School of Medicine (BUSM) carried out an exacting study that demonstrated the two forms did not differ with respect to sustaining 25-hydroxyvitamin D status (Journal of Clinical Endocrinology & Metabolism, Dec. 2007).

Also: Although dose was not raised as an issue, I'd be remiss if I did not mention that a 2007 risk assessment found that 250 micrograms/day (10,000 IU) in healthy adults is considered the tolerable upper limit. Readers will find information below with regard to Vitamin D toxicity that I extracted from the (on-line edition of the) Merck Manual as well as drug interactions that I obtained from an entry on the Office of Dietary Supplements (NIH) website.



http://www.merck.com/mmpe/sec01/ch004/ch004k.html

Vitamin D Toxicity

Usually, vitamin D toxicity results from taking excessive amounts. Marked hypercalcemia commonly causes symptoms. Diagnosis is typically based on elevated blood levels of 25(OH)D. Treatment consists of stopping vitamin D, restricting dietary Ca, restoring intravascular volume deficits, and, if toxicity is severe, giving corticosteroids or bisphosphonates.

Because synthesis of 1,25(OH)2D (the most active metabolite of vitamin D) is tightly regulated, vitamin D toxicity usually occurs only if excessive doses (prescription or megavitamin) are taken. Vitamin D 1000 μg (40,000 IU)/day produces toxicity within 1 to 4 mo in infants. In adults, taking 1250 μg (50,000 IU)/day for several months can produce toxicity. Vitamin D toxicity can occur iatrogenically when hypoparathyroidism is treated too aggressively (see Fluid and Electrolyte Metabolism: Treatment).

http://ods.od.nih.gov/factsheets/vitamind.asp#h9

Dietary Supplement Fact Sheet: Vitamin D


Office of Dietary Supplements ? National Institutes of Health
Interactions with Medications

Vitamin D supplements have the potential to interact with several types of medications. A few examples are provided below. Individuals taking these medications on a regular basis should discuss vitamin D intakes with their healthcare providers.

Steroids
Corticosteroid medications such as prednisone, often prescribed to reduce inflammation, can reduce calcium absorption [77-79] and impair vitamin D metabolism. These effects can further contribute to the loss of bone and the development of osteoporosis associated with their long-term use [78-79].

Other medications
Both the weight-loss drug orlistat (brand names Xenical? and alli?) and the cholesterol-lowering drug cholestyramine (brand names Questran?, LoCholest?, and Prevalite?) can reduce the absorption of vitamin D and other fat-soluble vitamins [80-81]. Both phenobarbital and phenytoin (brand name Dilantin?), used to prevent and control epileptic seizures, increase the hepatic metabolism of vitamin D to inactive compounds and reduce calcium absorption [82].



Anthony G. Payne, Ph.D.