Calcium Citrate 100% Pure Powder without any additives. Calcium comes in many forms but most research has been done on calcium carbonate which does not absorb well and it is in a much more concentrate form than calcium citrate. Calcium Carbonate is better if consumed with food unlike citrate which can be consumed without food. Citrate is easier to absorb but since it is not as concentrate it cost more. I do not consume much supplements since it is an unregulated industry. Most calcium citrate is sold with many other minerals like zinc, B6, magnesium, etc. which are unnecessary and unhealthy for body since according to many research from Europe those minerals interfere with the human body system. This is a pure calcium, without any additives and I consume this calcium without any food (although directions on the container advises you to consume with food), after my heavy workouts. I do that since calcium does not absorb easily specially with anything that has iron in it. I just add and mix it with just water, and nothing else. It does not dissolve in the water and should not since it is a powder, it only get it to my stomach. I fill the cup with water couple of times and mix every time so no powder is left on the bottom of the glass. No mixer, no fruit juice, absolutely nothing else. I do not take 1 1/2 spoon as advised, I take half since no reason to consume too much. Vitamin D3 needs to be reasonably high so calcium can be absorbed. For natural vitamin D, I consume Cod Liver in can not cod liver oil. Cod Liver cans come from cold waters of Atlantic. Very high in vitamin A and D. Human body can not consume more than 500 units of calcium at a time so brands selling 600 units is gimmick to sell the product. Put the calcium supplement into a glass of clear vinegar. This creates an acidic environment much like that of your stomach. Stir the solution occasionally. If the calcium supplement disintegrates within 30 minutes, it should dissolve in your stomach, too. If the calcium supplement does not completely dissolve, then forget it. Bravo.