Calcium is an essential dietary mineral that plays a vital role in muscle contraction, hormone secretion, nerve impulse transmission and bone growth and remodeling. Calcium is widely available in many foods, including dairy products, green leafy vegetables and fortified cereals, but many individuals choose to augment their dietary calcium intake with supplemental calcium. The dietary supplement industry uses the term "elemental calcium" to refer to the amount of calcium available for use by the body in a supplement.
Calcium forms compounds very easily and is never found in its elemental form in nature. Supplemental calcium also exists in the form of calcium compounds, usually calcium carbonate or calcium citrate. The amount of this substance found in a calcium compound varies depending on the compound. Calcium carbonate is 40 percent elemental calcium and 60 percent carbonate, but calcium citrate is only 21 percent elemental calcium. A calcium carbonate supplement with a total weight of 500 milligrams, of which 40 percent is elemental calcium, supplies the body with 200 milligrams of absorbable calcium.
It is important for users to know the amount of elemental calcium in a supplement because it is the elemental form of calcium that is important when determining how much calcium an individual must consume to meet the daily recommended dietary allowance (RDA) of the mineral. The RDA of calcium is 1,000 milligrams for adults ages 19 to 50 and 1,200 milligrams for adults ages 51 and older. Supplements that contain calcium should report both the amount of elemental calcium contained and percentage of the RDA of calcium that amount represents on their label. The ingredients should also list in what compound the calcium is found.
Calcium carbonate is best absorbed when taken with food. It should be avoided by individuals who have shellfish allergies, because it is manufactured from oyster shells. Calcium citrate can be taken without or without food and is safe for those who have shellfish allergies. Supplemental calcium can also be found in gluconate, lactate and phosphate compounds.
Experts recommend that individuals take no more than 500 milligrams of elemental calcium at one time, because the body cannot efficiently absorb more than that amount. Larger doses of supplemental calcium can be achieved by taking 500-milligram doses of elemental calcium multiple times per day. Calcium supplements can cause gas, bloating and constipation, but these symptoms can improve if large doses are spread through the day and taken with food.