Calcium : Chemistry and Biology

Calcium is an essential mineral that is required for the formation of bone, and is necessary for the cloning of blood, conduction of nerve impulses and contraction of muscle among other functions. Calcium is found naturally in foods, such as dairy products and can be added to certain foods, such as orange juice. Calcium is also available in dietary supplements. In all cases, calcium is found in these diet sources in the form of various calcium salts. The physical characteristics of the salts affect their actual elemental calcium content, solubility in various solvents and most importantly, their bioavailability. Bioavailability includes absorption, metabolism and excretion and each of these metabolic processes can be affected by the type of salt ingested. With regard to dietary supplements, the concentration of calcium in the salt also affects the size of the pill, the number of doses required to reach the recommended intake level and finally the cost. As an example, calcium carbonate contains 40% elemental calcium whereas calcium citrate contains 21% elemental calcium; both are equally well absorbed, yet the number of pills required to deliver 1000 mg of elemental calcium (100% of the daily value) with the citrate salt is twice the number needed with calcium carbonate, and the costs are greater with calcium citrate.