Vitamin D3 (cholecalciferol) is the preferred form of vitamin D, as it is effective at increasing vitamin D levels in the body. Vitamin D3 (Cholecalciferol): 25 mcg (1000 IU) – 500% NRV. Vitamin D3 plays an important role in overall wellness by contributing to the maintenance ofnormal bones, teeth, muscle function, and immune system function.