Home Ingredients Coral Calcium

Coral Calcium

Evidence Level
Preliminary
5 Clinical Trials
5 Documented Benefits
1/5 Evidence Score

Coral calcium is calcium carbonate made from ground coral, often fossilized coral or coral sand; the best-known products used coral from the Okinawa (Ryukyu) islands of Japan. Coral skeletons are built from aragonite, a crystal form of calcium carbonate, and the powder also carries magnesium and small amounts of other minerals. It became famous through infomercials in the early 2000s claiming it could treat cancer and other serious diseases and was absorbed up to 100 times better than other calcium. The US Federal Trade Commission (FTC) sued the promoters, alleging those claims were false and unsubstantiated, and the FTC and FDA warned website sellers. Human research on coral calcium itself is very thin: one 12-person, single-dose absorption study and one small uncontrolled study of a hydrogen-loaded product. Its safety limits and drug interactions are those of any calcium carbonate supplement.

Studied Dose Single dose of coral powder supplying 525 mg calcium (in crackers) in the one absorption study; 170 to 1,020 mg/day of a hydrogen-loaded coral calcium for 4 weeks in one small study. Adult calcium upper limit from all sources: 2,500 mg/day (ages 19 to 50), 2,000 mg/day (51 and older).
Active Compound Calcium carbonate (mainly aragonite) from ground coral, with magnesium and trace minerals; the Ryukyu coral powder used in Japanese research contained about 20% calcium and 10% magnesium by weight.

Benefits

Calcium absorption compared with calcium carbonate

In a crossover study of 12 healthy Japanese adults, crackers made with coral powder (525 mg calcium) raised urinary calcium, an indirect marker of absorption, somewhat more than crackers with the same calcium as calcium carbonate. It was a single-dose test in very few people, and the coral powder also carried magnesium. It does not support claims of absorption many times higher.

Supported by Trial 1

Calcium and magnesium from one ingredient

The Ryukyu coral powder used in Japanese research contained about 20% calcium and 10% magnesium by weight, so it supplies both minerals. For context, adults need 1,000 to 1,200 mg of calcium a day from food and supplements combined. Products vary, so check the elemental calcium and magnesium per serving on the label rather than the coral powder weight.

Supported by Trial 1, Trial 5

Bone measures in mouse studies of coral calcium

In mice with their ovaries removed, a model of bone loss after menopause, 6 months of a coral calcium diet restored total and cortical bone mass in the femur, with smaller effects at the tibia and spine. In young male mice, coral sand and fossil coral improved bone markers compared with calcium carbonate. These are animal results only.

Supported by Trial 4, Trial 3

Blood pressure in a rat study of coral sand

In spontaneously hypertensive rats, 8 weeks of a diet using coral sand as the calcium source lowered systolic blood pressure by about 16 mm Hg compared with a calcium carbonate diet. The researchers credited its soluble silica rather than its calcium. No human blood pressure trial of coral calcium was found in PubMed.

Supported by Trial 5

Triglycerides with a hydrogen-loaded coral calcium product

In a 4-week study of 16 Taiwanese adults with metabolic syndrome who took capsules of coral calcium loaded with hydrogen alongside their usual care, average triglycerides fell from about 193 to 152 mg/dL. There was no control group, other blood markers did not change significantly, and the maker funded the study, so the drop cannot be credited to the product.

Supported by Trial 2

Mechanism of action

1

Calcium carbonate that needs stomach acid to dissolve

Coral skeletons are made of aragonite, a crystal form of calcium carbonate. Like other calcium carbonate, it dissolves less readily when stomach acid is low unless taken with a meal, and calcium supplements in general are absorbed better with food. The share absorbed falls as the single dose rises, and absorption is highest at 500 mg of calcium or less.

2

Magnesium and trace minerals carried with the calcium

Coral powder brings magnesium and other minerals along with its calcium. The one human absorption study did not test why coral powder raised urinary calcium slightly more than calcium carbonate, and no human study has shown that the trace minerals in coral have effects beyond their calcium and magnesium content.

3

Soluble silica in coral sand (animal research)

Researchers in Okinawa found that diets made with coral sand contained more soluble silicon than other calcium sources. In mouse and rat studies they linked this silicon to better bone markers and lower blood pressure, partly through higher magnesium uptake by artery muscle cells. This is animal and cell work, not human evidence.

Clinical trials

1
Coral Powder vs Calcium Carbonate Crackers: Absorption Crossover in 12 Adults
PubMed

Crossover study comparing calcium absorption from crackers made with Ryukyu coral powder or with calcium carbonate, each supplying 525 mg calcium, with a 3-day washout and a no-cracker control. Absorption was judged from the rise in urinary calcium. (Ishitani et al. 1999, J Nutr Sci Vitaminol (Tokyo))

12 healthy adult volunteers in Japan (6 men, 6 women).

In the second half of the observation period, the rise in urinary calcium per dL of glomerular filtrate was greater after the coral crackers than after the calcium carbonate crackers (p = 0.039). The authors noted the small number of subjects. Urinary calcium is an indirect marker of absorption, each product was tested as a single dose, and no bone or long-term outcome was measured.

2
Hydrogen-Rich Coral Calcium Capsules in Metabolic Syndrome: 4-Week Case Series (maker-funded)
PubMed

Prospective case series with no control group. Patients were randomly assigned to 1, 3 or 6 capsules a day (170 mg of hydrogen-rich coral calcium per capsule), taken alongside their usual treatment for 4 weeks. The primary outcome was adverse effects; blood lipids were secondary. Funded by the maker, HoHo Biotech, which employed six authors and took part in design, data collection and the decision to publish. (Chiu et al. 2023, Front Nutr)

16 Taiwanese adults with metabolic syndrome (7 men, 9 women; mean age 62, range 32 to 80); 5, 5 and 6 patients in the three dose groups.

No obvious adverse effects were recorded. Average triglycerides fell from 193 to 152 mg/dL (p = 0.04, a within-group change), while HDL and LDL cholesterol, HbA1c, inflammatory markers and quality of life did not change significantly. With no control group, very small dose groups and patients on conventional treatment, the drop cannot be credited to the capsules. The product uses coral calcium as a hydrogen carrier and is not ordinary coral calcium.

3
Coral Calcium Complex and Bone Density in Postmenopausal Women: Registered Trial, No Results Posted
PubMed

Randomized, open-label (no masking) phase 2 trial with three arms for 48 weeks: a coral calcium complex fortified with vitamin D3 (Coral Complex 3), the same complex plus the prescription drug ibandronate, or ibandronate plus vitamin D3. Sponsored by Columbia University and run at the Osteoporosis Center of Armenia; completed March 2023. (Bilezikian et al. 2020, ClinicalTrials.gov NCT04321837)

60 postmenopausal women aged 50 to 75 with a bone density T-score below -2.5 (but not below -3.5) at one or more sites, who had not used calcium supplements in the past year.

Primary outcomes were changes in lumbar spine, femoral neck, total hip and forearm bone density at 48 weeks. As of the last registry update (May 2024) no results were posted, and no matching publication was found in PubMed in October 2026. The design had no placebo and no ordinary calcium carbonate arm, so it could not show that coral calcium beats other calcium.

4
Coral Calcium and Zeolite in Ovariectomized Mice: 6-Month Bone Study (animal)
PubMed

Animal study of diets containing coral calcium or zeolite fed for 6 months to sham-operated or ovariectomized female mice, with bone measured by DXA, peripheral quantitative CT and micro-CT. (Banu et al. 2012, Nutr Res)

Female C57BL/6 mice; no human participants.

In the distal femur, total and cortical bone mass was restored in ovariectomized mice fed coral calcium or zeolite, and trabecular number and bone volume ratio were higher. Protection was smaller at the proximal tibia and lumbar vertebrae. Results in mice do not show an effect in people.

5
Coral Sand Diet and Blood Pressure in a Rat Strain Bred for High Blood Pressure (animal)
PubMed

Animal study of 8-week diets using coral sand as the calcium source, or calcium carbonate with or without soluble silica, plus cell-culture work on aortic smooth muscle cells. (Maehira et al. 2011, Nutr Res)

Spontaneously hypertensive rats; no human participants.

Systolic blood pressure was 16 mm Hg lower with coral sand and 18 mm Hg lower with soluble silica than with the calcium carbonate control diet (207 mm Hg). The authors attributed the effect to silica raising magnesium uptake in artery cells, not to calcium. No human blood pressure trial of coral calcium was found in PubMed.

Side effects and drug interactions

Common Potential side effects

Gas, bloating and constipation, as with any calcium carbonate; calcium carbonate causes these more often than calcium citrate, especially in older adults with low stomach acid. Smaller doses spread through the day and taken with meals can help.
Too much calcium: keep total calcium from food, supplements and antacids within the adult upper limit of 2,500 mg/day for ages 19 to 50 and 2,000 mg/day from age 51.
Kidney stones: higher intakes of supplemental calcium might increase kidney stone risk.
Lead and other metals: natural calcium sources can carry traces of lead. In a Thai analysis of 18 calcium products, the natural raw calcium group (such as oyster, coral and animal bone, reported together) contained 0.106 to 0.384 mg of lead per kg, with small amounts of mercury and cadmium; coral was not reported separately. Choose a brand with published third-party heavy metal testing.
The hydrogen-loaded coral calcium study recorded no obvious adverse effects in 16 adults over 4 weeks; longer safety data on coral calcium products are lacking.

Important Drug interactions

Levothyroxine: calcium carbonate can reduce its absorption; the label says not to take it within 4 hours of a calcium carbonate supplement.
Quinolone antibiotics (ciprofloxacin, moxifloxacin and others): calcium reduces their absorption; take the antibiotic 2 hours before or 2 hours after calcium.
Dolutegravir (an HIV medicine): calcium can lower its blood levels substantially; the label says to take it 2 hours before or 6 hours after calcium supplements.
Lithium: long-term use can raise blood calcium, and adding calcium supplements could increase this risk.
Acid-reducing medicines: low stomach acid reduces how well calcium carbonate dissolves unless it is taken with a meal.

Frequently asked questions about Coral Calcium

Is coral calcium absorbed better than other calcium?

No large advantage has been shown. The one human comparison, in 12 Japanese adults, found a somewhat larger rise in urinary calcium after crackers made with coral powder than after crackers with calcium carbonate, an indirect single-dose measure. The FTC challenged infomercial claims of absorption up to 100 times better, and the 2004 settlement barred the promoters from unsupported claims that coral calcium is absorbed better than other calcium supplements.

What did US regulators do about coral calcium advertising?

In June 2003 the FTC sued the promoters of Coral Calcium Supreme, including Robert Barefoot and Kevin Trudeau, alleging that their infomercial claimed falsely and without substantiation that it could treat or cure cancer, multiple sclerosis, heart disease and other serious diseases. The FTC warned dozens of websites and the FDA warned numerous others. Barefoot and his companies settled in January 2004 and were barred from such claims for any coral calcium product. In June 2004 the FTC also sued the marketers of Coral Calcium Daily over similar claims; a complaint is not a court finding.

Does coral calcium contain lead?

It can contain traces. In a Thai analysis, natural raw calcium products such as oyster, coral and animal bone, reported as one group, contained 0.106 to 0.384 mg of lead per kg, with small amounts of mercury and cadmium. US testing of calcium supplements bought between 1996 and 2000 (bonemeal, dolomite, oyster shell and refined calcium; coral products were not among those tested) found lead in many natural and some refined products, with refined antacids among the lowest. Choosing a brand that publishes third-party heavy metal testing is a sensible precaution.

How is coral calcium different from regular calcium carbonate?

Chemically it is mostly calcium carbonate, in the aragonite crystal form that corals build, along with some magnesium and trace minerals. It follows the same rules as other calcium carbonate: take it with meals, keep single doses to about 500 mg of calcium, and stay within the adult upper limit of 2,000 to 2,500 mg a day from all sources. No human study has shown a health advantage over ordinary calcium carbonate.

Has coral calcium been tested for bone density in people?

Not in any published trial. A 48-week trial of a coral calcium complex in 60 postmenopausal women with low bone density was registered and listed as completed in 2023, but no results have been posted or published. The bone findings so far come from mice. Evidence on calcium and bone in general comes from other calcium forms; see our calcium carbonate page.

What is Coral Calcium?

Coral calcium is calcium carbonate made from ground coral, often fossilized coral or coral sand; the best-known products used coral from the Okinawa (Ryukyu) islands of Japan.

What is Coral Calcium used for?

NutraSmarts does not list Coral Calcium under a health category. What the research covers: In a crossover study of 12 healthy Japanese adults, crackers made with coral powder (525 mg calcium) raised urinary calcium, an indirect marker of absorption, somewhat more than crackers with the same calcium as calcium carbonate.

What is the recommended dosage of Coral Calcium?

The clinically studied dose is Single dose of coral powder supplying 525 mg calcium (in crackers) in the one absorption study; 170 to 1,020 mg/day of a hydrogen-loaded coral calcium for 4 weeks in one small study. Always follow the product label and check with a healthcare provider for personal advice.

Is Coral Calcium safe, and does it have side effects?

Side effects and cautions reported for Coral Calcium include: Gas, bloating and constipation, as with any calcium carbonate; calcium carbonate causes these more often than calcium citrate, especially in older adults with low stomach acid. Smaller doses spread through the day and taken with meals can help. It may also interact with some medications. Coral Calcium is not right for everyone, so check with a healthcare provider first if you are pregnant or breastfeeding, have a medical condition, or take prescription medication.

Does Coral Calcium interact with any medications?

Possible interactions include: Levothyroxine: calcium carbonate can reduce its absorption; the label says not to take it within 4 hours of a calcium carbonate supplement. Quinolone antibiotics (ciprofloxacin, moxifloxacin and others): calcium reduces their absorption; take the antibiotic 2 hours before or 2 ho… If you take prescription medication, check with a pharmacist or doctor before using it.

How strong is the scientific evidence for Coral Calcium?

NutraSmarts rates the evidence for Coral Calcium as Preliminary (1 out of 5). It is backed by 5 study summaries and 14 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.

References(14 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. Ishitani K, Itakura E, Goto S, Esashi T. Calcium absorption from the ingestion of coral-derived calcium by humans. J Nutr Sci Vitaminol (Tokyo). 1999;45(5):509-17. doi: 10.3177/jnsv.45.509.PubMedUsed to support: Crossover study in 12 healthy Japanese adults: crackers with Ryukyu coral powder (about 20% calcium and 10% magnesium) supplying 525 mg calcium raised urinary calcium per dL of glomerular filtrate more than calcium carbonate crackers (p = 0.039). Single doses, an indirect absorption marker and very few subjects.
  2. Chiu SH, Douglas FL, Chung JR, Wang KY, Chu CF, Chou HY, Huang WC, Wang TY, Chen WW, Shen MC, Liu FC, Hsiao PJ. Evaluation of the safety and potential lipid-lowering effects of oral hydrogen-rich coral calcium (HRCC) capsules in patients with metabolic syndrome: a prospective case series study. Front Nutr. 2023;10:1198524. doi: 10.3389/fnut.2023.1198524.PubMedUsed to support: Uncontrolled 4-week case series in 16 Taiwanese adults with metabolic syndrome taking 1, 3 or 6 capsules a day (170 mg each) of hydrogen-rich coral calcium with usual care: no obvious adverse effects; triglycerides fell from 193 to 152 mg/dL (p = 0.04); other lipids, HbA1c, inflammatory markers and quality of life did not change significantly. Funded by the maker, which employed six authors.
  3. Bilezikian JP (principal investigator), Columbia University. Coral Calcium's Effect on Bone Density in Postmenopausal Women With and Without Ibandronate (NCT04321837). ClinicalTrials.gov. 2020;First posted March 25, 2020; last updated May 9, 2024; accessed October 2026..SourceUsed to support: Not PubMed-indexed. Registry record of a randomized, open-label phase 2 trial in 60 postmenopausal women with low bone density: coral calcium complex with vitamin D3, the complex plus ibandronate, or ibandronate plus vitamin D3, for 48 weeks; status completed (March 2023) with no results posted.
  4. Banu J, Varela E, Guerra JM, Halade G, Williams PJ, Bahadur AN, Hanaoka K, Fernandes G. Dietary coral calcium and zeolite protects bone in a mouse model for postmenopausal bone loss. Nutr Res. 2012;32(12):965-75. doi: 10.1016/j.nutres.2012.09.009.PubMedUsed to support: Mouse study: 6 months of coral calcium or zeolite diets restored total and cortical bone mass in the distal femur of ovariectomized mice, with smaller protection at the proximal tibia and lumbar vertebrae. Animal evidence only.
  5. Maehira F, Motomura K, Ishimine N, Miyagi I, Eguchi Y, Teruya S. Soluble silica and coral sand suppress high blood pressure and improve the related aortic gene expressions in spontaneously hypertensive rats. Nutr Res. 2011;31(2):147-56. doi: 10.1016/j.nutres.2010.12.002.PubMedUsed to support: Rat and cell study: in spontaneously hypertensive rats, 8 weeks of a coral sand diet lowered systolic blood pressure by 16 mm Hg versus a calcium carbonate diet (207 mm Hg), and soluble silica by 18 mm Hg; the authors attributed the effect to silica raising magnesium uptake in aortic smooth muscle cells. Animal evidence only.
  6. Maehira F, Miyagi I, Eguchi Y. Effects of calcium sources and soluble silicate on bone metabolism and the related gene expression in mice. Nutrition. 2009;25(5):581-9. doi: 10.1016/j.nut.2008.10.023.PubMedUsed to support: Six-month study in weanling male mice comparing calcium carbonate, coral sand, fossil stony coral, fish bone and eggshell: soluble silicon was highest in the coral sand diet, and silicon, coral sand and fossil coral improved bone biochemical markers versus calcium carbonate. Animal evidence only.
  7. Rechav Z, Tambutté E, LeCloux IM, Anglemyer S, Beltz NE, Chou NA, Dixson-Kruijf BE, Domagk J, Larson AM, Lewis SW, Rich R, Saheed LO, Schwenk JL, Sengkhammee JS, Waltenberg CA, Ye J, Achinuq BQ, Venn AA, Tambutté S, Gilbert PUPA. Exponential crystallization in corals. Nat Commun. 2026;17(1):2870. doi: 10.1038/s41467-026-69215-4.PubMedUsed to support: Coral biology study; cited here only for the background fact that reef-building corals form their skeletons from aragonite, a crystal form of calcium carbonate (CaCO3).
  8. Bunyaratavej N, Buranasinsup S. Calcium supplement: humanity's double-edged sword. J Med Assoc Thai. 2011;94 Suppl 5:S56-8.PubMedUsed to support: ICP-MS analysis by researchers in Bangkok of 18 calcium preparations from the market, grouped as calcium carbonate salts, chelated calcium and natural raw calcium: calcium carbonate and natural raw calcium all contained lead (0.023 to 0.407 mg/kg); natural raw sources such as oyster, coral and animal bone, reported as one group, contained 0.106 to 0.384 mg/kg lead with small amounts of mercury and cadmium; chelated forms were free of lead.
  9. Scelfo GM, Flegal AR. Lead in calcium supplements. Environ Health Perspect. 2000;108(4):309-13. doi: 10.1289/ehp.00108309.PubMedUsed to support: Lead testing of 136 US calcium supplement brands bought in 1996 (bonemeal, dolomite, oyster shell, and refined or chelated calcium; coral was not named): two-thirds failed California's 1999 criterion of 1.5 micrograms of lead per daily calcium dose; refined antacids and infant formulas had the lowest lead.
  10. Ross EA, Szabo NJ, Tebbett IR. Lead content of calcium supplements. JAMA. 2000;284(11):1425-9. doi: 10.1001/jama.284.11.1425.PubMedUsed to support: Analysis of 21 nonprescription calcium carbonate products (7 natural oyster shell, 14 refined) in March 2000: 4 of 7 oyster shell products had measurable lead, about 1 microgram a day at 800 mg of calcium and 1 to 2 micrograms at 1,500 mg; 4 of 14 refined products had similar lead, up to about 3 micrograms a day at osteoporosis doses. Coral products were not tested.
  11. Federal Trade Commission. FTC and FDA Take New Actions in Fight Against Deceptive Marketing. FTC press release. 2003;June 10, 2003. FTC v. Kevin Trudeau et al., US District Court, Northern District of Illinois, filed June 9, 2003..SourceUsed to support: Not PubMed-indexed. The FTC sued Kevin Trudeau, Robert Barefoot, Shop America (USA) and Deonna Enterprises over Coral Calcium Supreme (described as purportedly made of marine coral from Okinawa), alleging that their infomercial claimed falsely and without substantiation that it could treat or cure cancer, multiple sclerosis, lupus, heart disease and chronic high blood pressure, that one serving equaled two gallons of milk in bioavailable calcium, and that it was absorbed up to 100 times better than common calcium supplements. The FTC warned dozens of website operators and the FDA warned numerous others for representing products as useful in preventing or treating serious diseases. A complaint, not a court finding.
  12. Federal Trade Commission. Marketers of Coral Calcium Product Are Prohibited from Making Disease Treatment and Cure Claims in Advertising. FTC press release. 2004;January 22, 2004. Stipulated final order entered January 15, 2004, US District Court, Northern District of Illinois, Civil Action No. 03-C-3904..SourceUsed to support: Not PubMed-indexed. Settlement barring Robert Barefoot, Deonna Enterprises and Karbo Enterprises from claiming that Coral Calcium Supreme or any coral calcium product can treat or cure cancer, multiple sclerosis, heart disease, high blood pressure or other serious diseases, and from unsupported claims that coral calcium is absorbed better than other calcium supplements. The FTC could collect royalties owed to Barefoot from the infomercial, with a $3 million clause triggered if the defendants misrepresented their finances.
  13. Federal Trade Commission. Marketers of Supreme Greens and Coral Calcium Daily Come under Fire from the FTC. FTC press release. 2004;June 3, 2004. Complaint filed June 1, 2004, US District Court, District of Massachusetts..SourceUsed to support: Not PubMed-indexed. FTC complaint alleging that Coral Calcium Daily was advertised as a means to prevent, treat and cure cancer and heart disease and to treat degenerative and autoimmune diseases including multiple sclerosis, lupus and Parkinson's disease, and alleging that these health claims and the claims of superior absorption were false and/or unsubstantiated. A complaint, not a court finding.
  14. Office of Dietary Supplements, National Institutes of Health. Calcium - Health Professional Fact Sheet. NIH Office of Dietary Supplements. 2026;Updated June 22, 2026..SourceUsed to support: Not PubMed-indexed. Government fact sheet: adult RDAs of 1,000 to 1,200 mg; upper limits of 2,500 mg/day (19 to 50) and 2,000 mg/day (51 and older); calcium carbonate is 40% calcium, dissolves less well with low stomach acid unless taken with a meal, and causes more gas, bloating and constipation than citrate; absorption is highest at doses of 500 mg or less; interactions with dolutegravir, levothyroxine, lithium and quinolone antibiotics; higher supplemental calcium might increase kidney stone risk.