Supplemental vitamin D comes in two forms: ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3).
They have generally been regarded as equivalent and interchangeable, but that notion is based on studies of rickets prevention in infants conducted seven decades ago.
Recent studies have shown that vitamin D3 is a more potent form of vitamin D. Vitamin D2 has a shorter shelf life, and its metabolites bind with protein poorly, making it less effective.
One unit of cod liver oil (containing vitamin D3) has been shown to be as effective as four units of Viosterol (a medicinal preparation of vitamin D2).
However, the form of vitamin D used in prescriptions in North America is almost invariably vitamin D2.
Source: American Journal of Clinical Nutrition October 2006; 84(4): 694-697
Editor's Note: After reading this article, I went to check mine. I am taking Exact Vitamin D 1000 U.I. (a Canadian Loblows no-name brand), Checking the bottle, it says that it is Vitamin D3.
Contraindications and Precautions:
Vitamin D is contraindicated in those with hypercalcemia and in those with evidence of vitamin D toxicity. Vitamin D is contraindicated in those with hypersensitivity to any component of a vitamin D-containing product.
Pregnant women and nursing mothers should avoid vitamin D supplemental intakes greater than U.S. RDA amounts of the vitamin unless higher amounts are prescribed by their physicians. The U.S. RDA for vitamin D is 400 IU or 10 micrograms daily.
Pharmaceutical use of vitamin D must only be undertaken under medical supervision.
Supplemental vitamin D should be used cautiously in those on digoxin or any cardiac glycoside. Hypercalcemia in those on digoxin may precipitate cardiac arrhythmias. Supplemental doses of vitamin D greater that upper limit intake levels (UL) should only be used if medically prescribed and should be avoided by those on digoxin or other cardiac glycoside. The UL for adults is 2,000 IU or 50 micrograms daily.
Concomitant use of thiazides and pharmacologic doses of vitamin D may cause hypercalcemia in some.
Source: Dr. Mercola's Comment and Importance of Vitamin D
Photo credit: NatureWise on Amazon.com
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