An abnormally high level of calcium in the blood is called hypercalcemia. It is commonly caused by overactivity of the parathyroid glands (small glands in the neck that help regulate the blood level of calcium).
Cancer may also cause hypercalcemia, either by spreading to bone or by producing abnormal hormones that cause bones to release calcium. Less commonly, the condition may result from too much vitamin D in the diet or from certain inflammatory conditions, such as sarcoidosis (thought to be due to overactivity of the immune system