Coral Calcium is an excellent source of calcium, the single most abundant mineral in our bodies. In addition to building healthy bones, calcium plays essential roles in muscle contractions, heartbeat, blood clotting, nerve transmission, and in converting signals from hormones in the blood into actions within cells. The vitamin D in this formula supports intestinal absorption of the calcium that you eat and its optimal use in the body. Adequate calcium and vitamin D throughout life in a healthful diet may reduce the risk of osteoporosis in later life. Source Naturals Coral Calcium is eco-friendly: It is harvested from fossilized (dead) coral and is not harmful to living coral.*