Form Comparison

Calcium Carbonate vs Microcrystalline Hydroxyapatite

How calcium carbonate and microcrystalline hydroxyapatite differ in elemental content, absorption, tolerance, and cost.

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Quick verdict. Carbonate is cheap, well studied, and absorbs well with meals. MCHC is ground bovine bone marketed for bone health with limited absorption data, and bone-derived calcium has carried lead in past testing. Choose carbonate (or citrate); if you buy MCHC anyway, insist on third-party certification.

Side by Side

Calcium Carbonate Microcrystalline Hydroxyapatite (MCHC)
Elemental content 40% elemental calcium Varies by product
Absorption Moderate Variable
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. Ground bovine bone with calcium, phosphorus, and bone matrix proteins. Absorption data are limited.
Typical dose 500-600 mg elemental per dose, with food Per product
Common uses general supplementation, antacid marketed for bone health
Side effects Constipation, gas, bloating. Constipation.
Cost Low Moderate
Also called calcium from oyster shell, calcified seaweed hydroxyapatite, bone meal concentrate
Labels in index 1,075 149

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 Microcrystalline Hydroxyapatite (MCHC)

There is rarely a reason to choose microcrystalline hydroxyapatite: carbonate or citrate are better studied. Bone-derived products have carried lead in past testing; look for certification.

Microcrystalline Hydroxyapatite (MCHC)

There is rarely a reason to choose microcrystalline hydroxyapatite: carbonate or citrate are better studied.

What to look for: Microcrystalline Hydroxyapatite 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 149 list microcrystalline hydroxyapatite.

Open supplement search

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.