Patient One Vitamin D3 5000 IU supplies cholecalciferol, a highly absorbable and bioavailable form of vitamin D (from lanolin), for optimal nutritional benefits for the skeletal, cardiovascular and immune systems. Vitamin D3 is the naturally occurring form of vitamin D synthesized in humans. Studies show that plant-derived D2 is metabolized differently than D3 and that D3 may be over 3 times more effective than D2 in raising and maintaining serum vitamin D levels. Vitamin D3 is most noted for optimizing calcium bioavailability, thereby promoting peak bone mass and bone strength. Patient One Vitamin D3 5000 IU is a professional-strength medinutritional formula that promotes compliance through once-a-day high-potency administration.