Calcium is an essential mineral. The adult skeleton contains about 1,200 grams of calcium, 99% of which is stored in the bones and teeth. The remaining 1% of calcium (about 10-12 grams) circulates within the body in a soluble form. The role of calcium in maintaining strong bones and teeth is well known. Lesser known is the vital role soluble calcium plays in neuromuscular and cardiovascular function, in coagulation, as an intracellular second messenger for cell surface hormone action, and in gene transcription, cellular growth, and metabolism.  A synergistic relationship exists between calcium and magnesium. When the amount of magnesium in the bloodstream falls, the kidneys readjust the balance by holding onto less calcium. When magnesium concentration rises, the kidneys excrete less calcium. Therefore, the more magnesium a person ingests, the more calcium is kept in the person's body.