Calcium is an essential mineral necessary for strong bones, muscle function and a variety of biochemical reactions in the body. According to the National Institutes of Health, the Dietary Reference Intake for calcium for adults is between 1,000 and 1,300 mg daily, depending on age and gender. Dairy products are great sources of calcium, but for those who don't consume dairy-based foods, supplements might be required. Calcium supplements differ in purity, bioavailability and absorbability.
Calcium Carbonate
Calcium carbonate is the most used and least expensive type of calcium supplement. According to CalciumInfo.com, 85 percent of calcium supplements sold in the United States are made from calcium carbonate. Calcium salts contain elemental calcium, which is what the body absorbs and utilizes, but not all calcium salts contain the same amount. For example, calcium carbonate contains approximately twice the amount of elemental calcium by weight compared to calcium citrate.
Calcium is absorbed in the small intestines. It is absorbed more efficiently in high acidity. Therefore, calcium carbonate is best absorbed with meals because of the release of stomach acid. The amount of calcium absorbed is also dependent on vitamin D, magnesium and estrogen levels.
Calcium Citrate
Calcium citrate combines calcium salt with citric acid, which is more complimentary for the absorption of elementary calcium. Calcium citrate does not have to be taken with meals. It is a better choice for people with reduced stomach acid production. Fortified fruit juices often contain calcium citrate, which may not be well tolerated by people with acid reflux disease. Because calcium citrate usually contains less elemental calcium per tablet, more tablets must be taken daily.
Taking more than 500mg of elemental calcium at one time is not efficient, because the body cannot absorb more than 500mg at one time, according to "Advanced Nutrition and Human Metabolism." However, some supplement labels do not list elemental calcium content, only total content per tablet. For example, a 500mg tablet of calcium carbonate contains about 200mg of usable elemental calcium, whereas the same sized calcium citrate tablet would provide about 100mg.
Coral Calcium
Coral calcium is mined from fossilized coral beds, which are above-ground limestone deposits that were once part of a coral reef. Coral calcium is composed primarily of calcium carbonate with some magnesium and other trace minerals. Coral has a chemical structure and composition that is similar to human bone and thought to be better assimilated within the body than synthetic calcium carbonate. Coral calcium may have benefits beyond that of its elemental calcium content, although exaggerated health claims over the years have caused controversy and confusion. There are some legitimate concerns regarding contamination, as some coral calcium supplements from Okinawa, Japan, have relatively high amounts of lead and mercury.
Other Types
Naturally occurring calcium occurs within oyster shell material, dolomite and bone meal products, although contamination with lead can be a concern because calcium supplements are not tested by any regulatory agency for lead, as noted by "Doctor's Complete Guide to Vitamins and Minerals."
Calcium gluconate and calcium lactate are both uncommon types of supplements, because both contain low elemental calcium content. Calcium phosphate is the principle form of calcium in cow's milk, and contains nearly the same percentage of elemental calcium as calcium carbonate, but it's not nearly as economical to produce as a supplement.
References
- National Institutes of Health: Office of Dietary Supplements: Calcium Fact Sheet
- CalciumInfo.com: Calcium Types
- "Advanced Nutrition and Human Metabolism: 5th Edition"; Sareen S. Gropper and Jack L. Smith; 2009
- "The New Encyclopedia of Vitamins, Minerals, Supplements, and Herbs"; Nicola Reavley; 1999
- "Doctor's Complete Guide to Vitamins and Minerals"; Mary Dan Eades and Philip Lief; 2002
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