This combination product contains vitamins, minerals and other nutrients that help to strengthen bone, a living tissue that requires constant upkeep. Most important in the combination, is calcium, which ensures that bones stay healthy and strong. Also crucial is vitamin D, which helps the body absorb calcium from foods, and prevents calcium loss in the urine. The mineral magnesium is essential for assisting bone in creating new calcium crystals. Of course, these and other key nutrients (from vitamin K to trace minerals such as manganese, boron, and zinc) can be taken individually. But for greater ease, a bone-building formula combining them all can be very convenient.