Coral calcium's increased bioavailability may be partially due to its magnesium content, which ranges from about 0.5-20% in commercial products.

Many forms of calcium supplements are now on the market and all advertise attractive benefits. With the high rates of osteoporosis in the U.S., the fact that many Americans do not get enough calcium, the recent review published by and the sales of calcium supplements in the U.S. in 2001 being some $775 million (according to the Nutrition Business Journal), the controversy as to which form of calcium provides the most benefit seems never more important.

However, the closer calcium supplementation is examined, the more questions arise. To ascertain the best regimen for calcium supplementation, important factors are not only cost and the bioavailability of individual calcium forms, but also associated nutrients, how well the supplement is tolerated and retained in the tissues, as well as what other lifestyle factors might contribute to a calcium supplement regimen.

Recent Review Fuels Calcium Controversy (White Plains, N.Y.) released a review of calcium supplements in June this year—with the bad news that 20% of calcium supplements tested had problems. Of the 25 calcium supplements analyzed, two contained lead in excess of California's "no significant risk level." Additionally, one of these products failed to break apart during disintegration testing, and a third product contained only 77% of the labeled amount of calcium.

Other issues haunt popular calcium supplements present and past. For example, unrefined calcium sources such as oyster shell, bone meal, and dolomite were once popular but have fallen out of favor due to high levels of toxic metals (such as lead). Here's a look at other products currently in the spotlight.

• Coral Calcium. Coral calcium is the current leader of the calcium supplement controversy. Manufacturers of these products assert that their calcium is one of the most bioavailable, supported by the claim that Okinawan's native population (where coral calcium is produced) has a very low incidence of disease and high longevity. There is some research that shows coral-derived calcium is better absorbed than "pure" calcium carbonate, perhaps due—in part—to factors such as coral calcium's magnesium content. Depending on the brand, coral calcium generally contains some 20-40% calcium and 0.5-20% magnesium. Since the calcium to magnesium ratio varies between brands (and source), some companies are adding magnesium to increase its ratio.

Another issue involves the sustainability of the source of coral calcium. Many are aware of the serious environmental deterioration of coral reefs, and there is concern that gathering coral calcium contributes to this problem. Manufacturers claim to be mining in eco-friendly ways, taking the coral only from the beach or the ocean floor so as not to disturb the living coral reefs. However, some argue that harvesting the dead coral lying on the ocean floor disturbs the sediment, which harms living coral.

Tod Cooperman, M.D., president of, said in a recent press release, "We have received many questions from consumers about coral calcium. Coral calcium is not inherently better or worse than other types of calcium. But it is sadly ironic that the most advertised brand also had the most lead."

The Council for Responsible Nutrition (Washington) also has asked the Food and Drug Administration (FDA) to crack down on the "miracle cure"-type claims that these manufacturers are making on the coral calcium products.

• Calcium Carbonate. Calcium carbonate is the least expensive and most common calcium form on the market and is found, for example, in antacid tablets such as Tums. An estimated 85% of all calcium supplements contain calcium carbonate. Calcium carbonate is also the most concentrated form of calcium (Ca++) on the market, giving two times the elemental calcium by weight as the citrate form, allowing for smaller quantities of use. Calcium carbonate in antacids requires stomach acid to dissolve and has a potent "neutralizing" or buffering effect. Long-term use of calcium carbonate antacids, however, may result in side effects and is associated with gastric reflux, gas, constipation and bloating. Calcium carbonate is not absorbed as well as the citrate form, especially in people with low gastric acid levels, such as the elderly. Calcium carbonate and citrate both partially inhibit the absorption of iron when taken with food.1

• Calcium Citrate. The second most inexpensive and common form of calcium on the market is calcium citrate. Calcium citrate has been shown in a meta-analysis to be better absorbed than calcium carbonate by approximately 22-27%—either with meals or on an empty stomach.2 Calcium citrate does not need as low a pH to dissolve as calcium carbonate. Calcium citrate, but not carbonate, enhances the absorption and deposition of aluminum from food sources into human tissues (Nolan, 1994).

• Calcium Chelates. Amino acid chelates, generally, are superior forms of minerals for absorbability, but have cost considerations. Additionally, some supplement suppliers carry what they claim to be amino acid chelates, when they are not. The National Nutritional Food Association - NNFA (Newport Beach, Calif.) defines a chelate very specifically, and several criteria must be met in order for chelation to actually occur. Of the claimed "chelates" on the market are the various Krebs (Citric Acid) Cycle chelates, such as citrate, malate, and aspartate. Dicalcium malate is a newer form of a true calcium chelate. It contains a high amount of calcium (30%).

Milk is the most fundamental source of calcium and has spawned "milk calcium" supplements. Here, the California Milk Processor Board is working with McDonald's to encourage kids to drink milk.

• Milk Calcium. Considering all the forms of calcium, the most fundamental source should not be forgotten. Calcium from milk is one of the best known food/nutrient associations, and now there are "milk calcium" supplements on the market. For example, one consumer supplement contains a calcium supplement in a colloidal form, as it is in milk, with additional bone nutrients of phosphorus and potassium. Another "milk calcium" claims to replenish glutathione levels in our cells, thereby bolstering the immune system. Research to resolve these issues has been ongoing for some time. For example, a 1987 study by Sheikh et al. concluded there was no significant difference in calcium absorption from carbonate, acetate, lactate, gluconate, and citrate salts of calcium, and from whole milk, in "fasting healthy young subjects."3 Other studies have produced different results.

Enough Calcium is Not Enough
A primary reason for calcium supplementation is for the prevention of osteoporosis. But Susan Brown, Ph.D., of the Osteoporosis Education Project (East Syracuse, N.Y.), reminds one that osteoporosis prevention requires a focus beyond calcium (and the hormone estrogen). She believes the best bone health is achieved by adopting an alkaline diet that reduces the bone loss process. Additional factors are important:

1. Growing healthy bones in childhood and adulthood,
2. Regular exercise (especially weight-bearing),
3. Adequate vitamin D, through the diet, supplements and exposure to sunshine,
4. Adequate vitamin K, such as with green, leafy vegetable consumption,
5. Appropriate levels of vitamin A,
6. Limiting caffeine intake—although not yet definitive, evidence exists that four or more cups of coffee per day increases fractures, and
7. Avoiding a high protein intake; this results in acids being released into the bloodstream, and the body then neutralizes them by removing calcium from bones and excreting it.

Researchers will continue to investigate the best formats for increased calcium absorption and manufacturers will continue to offer an array of calcium products. For example, in the food arena, there is much interest in the ability of prebiotics (types of dietary fiber that support probiotic culture growth) to increase calcium uptake. (See the "Ingredients in Use: Inulin and FOS" in this issue.)

Bioavailability, source sustainability, cost and marketplace positioning are just some of the issues that will continue to impact the development of calcium products for consumers.

Editor's Note:

With the goal of enhancing a food or beverage's calcium content, there are dozens of market forms of calcium to choose from. "One has to select an appropriate form of calcium to deliver the desired level, without affecting sensory properties and mouthfeel aspect of the finished product," notes Ram Chaudhari, Ph.D., senior executive vice president of R&D with a nutritional ingredient supplier. Calcium carbonate is, perhaps, the most cost-effective source of calcium.


However, it has a tendency to give chalkiness, as does dicalcium phosphate. Some of these defects can be avoided if a blend of calcium sources is used instead of a single source. In addition, these calcium salts are not very soluble; therefore, it is desirable to add calcium citrate or organic acid to improve solubility. In order to get the most out of these salts, the pH must be decreased to solubilize. Absorption then would increase.

"In general, in order to have more absorption, it is necessary to have soluble calcium salts. Indeed, there are advantages and disadvantages to have more soluble or insoluble forms, as shown in the accompanying chart," says Chaudhari.

—Claudia D. O'Donnell, Chief Editor

Forms for Fortifying Food

Calcium Form: Soluble Insoluble Blend of Calcium Sources
Examples of types:

Calcium gluconate

Calcium lactate

Calcium carbonate

Dicalcium phosphate

Calcium citrate
Dicalcium phosphate
Calcium lactate
Absorption: Higher Lower (organic acid Acceptable absorption
addition improves)
Acceptable absorption
Comments: Possible interaction with product and flavor impact Could give sediment, chalkiness, gritty mouthfeel Technologically a good solution
Source: Fortitech Inc.

On the Web: Calcium and Supplements



1 Cook, J.D., et al., 1991. "Calcium Supplementation: Effect on Iron Absorption," American Journal of Clinical Nutrition, 53:106-111.
2 Sakhaee K., et al., 1999. "Meta-analysis of Calcium Bioavailability: A Comparison of Calcium Citrate with Calcium Carbonate." Am J Ther. Nov; 6(6):313-21.
3 Sheikh, M.S., et al., 1987. "Gastrointestinal Absorption of Calcium from Milk and Calcium Salts," New England Journal of Medicine, 317:532-536.

See Also:

Ishitani K., et al., 1999. "Calcium Absorption from the Ingestion of Coral-derived Calcium by Humans," J. Nutr Sci Vitaminol (Tokyo). Oct; 45(5):509-17.
Levenson, D.I. and R.S. Bockman, 1994. "A Review of Calcium Preparations," Nutrition Reviews, 50: 221-232.