Calcium is toxic in overdose quantities, and can cause kidney damage - surplus calcium is deposited in the form of calculi (stones) in the kidney or bladder, or as tartar on the teeth.The body has mechanisms for regulating absorption and disposing of any excess, excreting it in the faeces, urine and sweat. The way that the body uses calcium is a bit complicated: it competes with magnesium, and both minerals need to be present in the correct proportions for each to function as it should. If there are high calcium levels in the blood, magnesium can help to reduce them, while calcium can help deal with potassium deficiencies. Many minerals and trace elements are interdependent in this way.