CALCIUM is a mineral that is necessary for life. The daily allowance of calcium for adult is 1,000 milligrams per day. The various salts of calcium like calcium carbonate, calcium citrate etc have different level of bio available calcium and different level of intestinal absorption. The calcium carbonate require acidic medium in stomach to get absorbed, thus absorption in people taking PPI or other medication for acid suppression decreases a lot. The main advantage of Calcium Citrate and Maleate is that, its absorption is not dependent on acid in stomach. VITAMIN D is a fat-soluble vitamin that helps your body absorb calcium and phosphorus. All calcium preparation comes fortified with vitamin D.