Calcium (Ca) is an essential nutrient that helps to form strong bones and teeth. This naturally occurring substance is the most abundant mineral in the human body. Calcium is also necessary for blood clotting and muscle function. It is well known that calcium can prevent osteoporosis and bone defects. The only source of calcium is our food. It exists in some foods, or it is added to other foods for fortification. Calcium can also be used as a dietary supplement and is present in certain medicines.