Hypercalcemia is a condition in which the calcium level in the blood becomes too high. Too much calcium in the blood can weaken bones and create kidney stones. It also can affect the heart and brain. Most often, hypercalcemia happens after one or more of the parathyroid glands make too much hormone. These four tiny glands are in the neck, near the thyroid gland. Other causes of hypercalcemia include cancer, certain other medical conditions and some medicines. Taking too much of calcium and vitamin D supplements also can cause hypercalcemia. Some people have no symptoms of this condition. Others have symptoms that range from mild to serious. Treatment depends on the cause.