Calcium Calcium Calcium is a chemical element with symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust and the third most abundant metal, after iron and aluminium. The most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life; gypsum, anhydrite, fluorite, and apatite are also sources of calcium. The
Calcium citrate for supplementation. According to recent research into calcium absorption after gastric bypass surgery, calcium citrate may have improved bioavailability over calcium carbonate in Roux-en-Y gastric bypass patients who are taking calcium citrate as a dietary supplement after surgery. This is mainly due to the changes related to where calcium absorption occurs in the digestive tract of these individuals. Calcium citrate Calcium citrate is the calcium salt of citric acid. It is commonly used as a food additive (E333), usually as a preservative, but sometimes for flavor. In this sense, it is similar to sodium citrate. Calcium citrate is also found