Traditionally, Vitamin D2 was the only non-animal source of Vitamin D and therefore the only source suitable for a range of demographics including individuals with a Vegan or Vegetarian diet.
A 2011 study published in the Clinical Journal of Endocrinology Metabolism compared Vitamin D2 to Vitamin D3 and concluded that “D3 is approximately 87% more potent in raising and maintaining serum 25(OH)D concentrations and produces 2- to 3-fold greater storage of Vitamin D than does equimolar D2.”
A 2006 article published in the American Journal of Clinical Nutrition compared Vitamin D2 to Vitamin D3 and made a stark conclusion that due to “the inefficiency of Vitamin D2 compared with Vitamin D3, on a per mole basis, at increasing 25(OH)D”, that “Vitamin D2 should no longer be regarded as a nutrient appropriate for supplementation or fortification of foods.”
Vitamin D2 chemically is not as stable as Vitamin D3, and published research clearly suggests efficacy is significantly inferior.
The role of Vitamin D2 in the marketplace was traditionally to be the vegetarian alternative Vitamin D3. VegD3® takes away the problem, and allows Vitamin D3 to be used in place of inferior Vitamin D2 across all applications.