Vitamin D and calcium. Conceptual image of human skeletons with pills and a molecular model (orange) of a form of vitamin D, with question marks representing the health claims relating to taking tablets containing calcium and vitamin D. It has been claimed that this combined mineral and vitamin pill can improve bone density in women over the age of 50 and reduce the risk of bone fractures due to osteoporosis. The molecule shown here is vitamin D3 (cholecalciferol).