Form Comparison

Calcium Carbonate vs Tricalcium Phosphate

How calcium carbonate and tricalcium phosphate differ in elemental content, absorption, tolerance, and cost.

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Quick verdict. Both absorb about equally with food, and both can constipate. Tricalcium phosphate also supplies phosphorus, which most diets already provide in plenty, so it matters mainly for older adults with low phosphorus intake. Choose carbonate for the most calcium per dollar and phosphate only if a clinician flags low phosphorus.

Side by Side

Calcium Carbonate Tricalcium Phosphate
Elemental content 40% elemental calcium 38.8% elemental calcium
Absorption Moderate Moderate
How it is absorbed Needs stomach acid to dissolve. Taken with a meal it is absorbed about as well as citrate; fasting or on acid suppression, absorption falls. Absorbed about as well as carbonate when taken with food; supplies phosphorus as well.
Typical dose 500-600 mg elemental per dose, with food 500-600 mg elemental per dose
Common uses general supplementation, antacid general supplementation
Side effects Constipation, gas, bloating. Constipation.
Cost Low Low
Also called calcium from oyster shell, calcified seaweed calcium phosphate
Labels in index 1,075 209

When to Choose Calcium Carbonate

Choose calcium carbonate when you take it with meals and do not use acid-suppressing drugs. The most calcium per tablet and the lowest cost. Oyster shell and algae sources are still mostly carbonate.

Calcium Carbonate

The most calcium per tablet at the lowest cost. Works well with meals in people with normal stomach acid.

What to look for: 500-600 mg elemental calcium per serving, taken with food. Expect some constipation.

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When to Choose Tricalcium Phosphate

Choose tricalcium phosphate when phosphorus intake is low, as in some older adults. Rarely needed for its phosphorus; most diets supply plenty.

Tricalcium Phosphate

Choose tricalcium phosphate when phosphorus intake is low, as in some older adults.

What to look for: Tricalcium Phosphate named on the Supplement Facts panel, with the amount per serving stated.

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Products on Titrate

In Titrate's index of NIH label data, 1,075 labels named as calcium products list calcium carbonate and 209 list tricalcium phosphate.

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Calcium does not have its own search category yet. Each product above links to its full label in the NIH database.

Related

References

NIH Office of Dietary Supplements. Calcium: Fact Sheet for Health Professionals.

Recker RR. Calcium absorption and achlorhydria. N Engl J Med. 1985;313(2):70-73.

Heaney RP, Dowell MS, Bierman J, Hale CA, Bendich A. Absorbability and cost effectiveness in calcium supplementation. J Am Coll Nutr. 2001;20(3):239-246.

Jackson RD, LaCroix AZ, Gass M, et al. Calcium plus vitamin D supplementation and the risk of fractures. N Engl J Med. 2006;354(7):669-683.

Bolland MJ, Avenell A, Baron JA, et al. Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. BMJ. 2010;341:c3691.

Bolland MJ, Grey A, Avenell A, Gamble GD, Reid IR. Calcium supplements with or without vitamin D and risk of cardiovascular events: reanalysis of the Women's Health Initiative limited access dataset and meta-analysis. BMJ. 2011;342:d2040.

Kopecky SL, Bauer DC, Gulati M, et al. Lack of evidence linking calcium with or without vitamin D supplementation to cardiovascular disease in generally healthy adults: a clinical guideline from the National Osteoporosis Foundation and the American Society for Preventive Cardiology. Ann Intern Med. 2016;165(12):867-868.