Back to chemistry class for you! There are actually several different types of vitamin D, two of which are found in supplements: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). But what is the difference between these two forms of vitamin D and which one is best?
Vitamin D₃ (cholecalciferol) is the form of vitamin D that is naturally made by our bodies after the skin is exposed to direct sunlight. It can also be found in vitamin supplements and foods, such as fortified milk, fatty fish, fish liver oil, and egg yolks. However, the body can’t actually use vitamin D3 until it is changed into an active form of vitamin D by the liver and kidneys.
Since vitamin D3 is naturally found in the human body, it is generally considered the preferred form of vitamin D supplementation . Ddrops® products contain this type of vitamin D, D3, which is obtained from lanolin that is sourced from sheep’s wool.
Vitamin D₂ (ergocalciferol) can also be found in supplements and comes from plant and/or fungal sources that are irradiated. There is some controversy about whether vitamin D₂ should be used as a supplement because it is not the form of vitamin D naturally made by the body. Evidence also shows that our bodies can store vitamin D3 better than vitamin D2 and that vitamin D3 raises blood levels of vitamin D quicker . Similar to vitamin D3, vitamin D2 still requires activation by the liver and kidneys. One available supplement that contains vitamin D2 (ergocalciferol) is Vegan Ddrops®.
There is a third form of vitamin D, 25-hydroxyvitamin D or 25(OH)D (calcidiol), that is naturally made in the liver. It is the most abundant form of vitamin D found in blood and is the form that is measured in blood tests to determine a person’s vitamin D levels. This form is actually still not active in the body, but it is a metabolite that signals the presence of vitamin D in the body.
1,25-hydroxy vitamin D (1,25(OH)2D) is the active form of vitamin D in the body. It is made by the kidneys from circulating 25(OH)D found in the blood. When active vitamin D binds with the vitamin D receptor (VDR) it acts like a switch that turns on a number of genetic activities. Researchers have discovered over 200 target genes for active vitamin D in almost every organ of the body.
Updates and edits by Carrie Noriega, MD, FACOG.
 Houghton, Veith R. The case against ergocalciferol (vitamin D₂) as a vitamin supplement . Am J Clin Nutr 2006;84:694-7.
 Dusso AS, Brown AJ, Slatopolsky E. Vitamin D. Am J Physiol Renal Physiol 2005;289(1):F8-F28
 Tripkovic L, Lambert H, Hart K, et al. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. Am J Clin Nutr. 2012 Jun; 95(6): 1357–1364.