Calcium is an important mineral for growth, maintenance and reproduction of human cells. It is necessary to form bones. The body cannot make use of calcium unless active vitamin D is present. When you have kidney disease, your kidneys cannot activate the vitamin D, so the calcium from the food you eat cannot be absorbed. As a result, your blood level of calcium can drop and your bones can become brittle and break more easily. Calcium supplements are administered both orally or by injection.