Calcium plays a critical role in the body. It is essential for normal functioning of nerves, cells, muscle and bone. Vitamin D improves the absorption of calcium into the body. Calcium supplements are used to treat or prevent low blood calcium levels. Calcium may be prescribed for treatment of osteoporosis (bone loss), osteomalacia (brittle bones), rickets, tetany, parathyroid disease. Calcium supplements are often used to ensure an adequate dietary intake in conditions such as pregnancy, nursing, kidney disease, pancreatitis or during therapy with anti-seizure medications.