D3 Optimal delivers 2000 IU of the preferred form of vitamin D, as vitamin D3, in each tablet. The active form of vitamin D in the body is 1,25 dihydroxyvitamin D—1,25 (OH)2D3. Dietary vitamin D must be converted into this active form in order to deliver the health benefits associated with vitamin D. Iso D3 is designed to support optimal metabolism of vitamin D to its active form.