The role of Vitamin D in helping to  maintain bone density and strenght is clear. It is required for the process of moving calcium through the intenstinal wall into the bloodstream.
Even though the human body can manufacture vitamin D under ideal circumstances, there is strong evidence that much of the American population suffers from a deficiency of the nutrient. This means that supplmentation may be important.
Cholecalciferol (D3) is a natural, highly bioavalable form of Vitamin D derived from lanolin.