HI DEE® (Vitamin D3 (Cholecalciferol)) which maintains a healthy Calcium Phosphorus levels in the body for strong bones and increases muscle strength in older adults, and it also plays an active role in a healthy immune response. Vitamin D3 (Cholecalciferol) is the optimal form of vitamin D. It is the form of vitamin D that the body synthesis when the skin is exposed to UV radiation from sunlight (but the ability to do so decreases as we age), Cholecalciferol is the most active form of vitamin D that covers the body’s need efficiently.