Calcium Carbonate is the cheapest form of Calcium. It is made from oyster shell, rock, coral, bone, eggshells, and various other items. This form is hard to digest and assimilate, requiring other minerals and vitamins to complete the task of absorption. This means now you are buying more items to get calcium. Why not purchase Calcium in Apatite, Citrate, Orotate or Phosphate (MCHC) form and have minimal chemical processing (which takes more of your energy) to receive the full benefit of the mineral. By purchasing the inferior form of calcium, and having to add in additional elements to help receive the calcium, you run the risk of having too much of the other elements in your system which then your body is taxed on getting rid of the excess, or it stores it due worn out mechanisms for dismantling the excess. This then leads you to having to take something else to rid yourself of the excess. Yikes sounds like how drugs work. Take this drug and have a side effect, so then take another drug to combat the side effect of the first. Option two; just take calcium carbonate and hope for the best. The probability of gallstones, kidney stones, liver stones, bone spurs and a whole host of other inflammatory issues may await you. My goal is for you to take only what you need, no more, no less in a form that is suitable for you. Because calcium comes in so many different forms, the milligrams differ in absorbability. Therefore, be cautious to how much you ingest. The RDA (Recommended Daily Allowance) and AMA (American Medical Association) state 1500mgs daily for those over 50 years old, is based off calcium carbonate, knowing that your body will probably only absorb approximately 30% of it. Where another form can be absorbed approximately 98%, concluding less milligrams is needed.