Calcium carbonate

Grades and forms

Calcium carbonate is the most concentrated common calcium source for food supplements. It contains 40.0 % elemental calcium, so 250 mg of powder delivers 100 mg of calcium. It is a white powder, practically insoluble in water, and manufacturers buy it as a fine powder or as granulated grades for tableting.

The material on the market comes from two routes. Precipitated calcium carbonate is produced by a chemical precipitation process and is usually finer and more uniform. Ground calcium carbonate is milled from natural mineral sources. The route affects particle shape, flow and the impurity profile, so it belongs in the specification you agree with your supplier.

Granulated, directly compressible grades combine calcium carbonate with a binder. They run better on high-speed tablet presses, but the binder dilutes the calcium. For these grades, use the calcium content on the specification instead of the 40.0 % theoretical value.

The choice depends on the format, the label claim per unit and the purity criteria your dossier must meet. SoleChem sends the specification sheet and certificate of analysis with its quote. Ask for the grade you need in the quote form.

EU regulatory status

Calcium carbonate is listed as a source of calcium in Annex II of Directive 2002/46/EC, so it may be used in food supplements throughout the EU. It is also listed for addition to other foods in Annex II of Regulation (EC) No 1925/2006. The site guide to permitted vitamin and mineral forms explains how the two annexes relate.

As a food additive, calcium carbonate is E170, authorised under Regulation (EC) No 1333/2008. Specifications for authorised food additives are set in Regulation (EU) No 231/2012; check the E170 entry there. Under Article 4(3) of Directive 2002/46/EC, purity criteria set in Union law for other food uses also apply to Annex II substances, so the E170 specification is the purity reference when the material is used as a calcium source in supplements.

Maximum amounts of calcium in food supplements are not yet harmonised at EU level. Each member state sets its own rules, and the figures differ. See maximum levels by EU country before fixing a label claim for several markets.

Formulation notes

The label-claim arithmetic is simple because the calcium content is high:

• 100 mg calcium per serving needs 250 mg of calcium carbonate.
• 500 mg calcium per serving needs 1,250 mg of calcium carbonate.
• 800 mg calcium per serving needs 2,000 mg of calcium carbonate.

These figures assume pure material at 40.0 %. Recalculate with the assay on the certificate of analysis, or use the elemental content calculator.

In tablets, high claims mean heavy tablets. Plain powder compresses poorly, so formulators use granulated grades or add binders. In capsules, fill volume limits the calcium per capsule, and high claims usually need more than one capsule per serving.

Calcium carbonate reacts with acids and releases carbon dioxide. In effervescent tablets this reaction can form part of the effervescent system. In powder blends with citric or malic acid, moisture can start the reaction and cause gassing in sealed packs.

Because it is practically insoluble, it settles in drinks and needs suspension aids, or a soluble salt instead. It gives a chalky mouthfeel in chewables and powders. It is alkaline, so check its effect on the pH of mixtures containing acid-sensitive actives.

How calcium carbonate compares to other forms

Calcium carbonate has the highest calcium content per gram in this set. Calcium citrate needs about 1.7 times the powder mass for the same claim, and the hydrated material contains less calcium than the anhydrous figure. The phosphates also add phosphorus to the formula. The calcium carbonate vs calcium citrate comparison and the calcium forms guide cover the trade-offs in more detail.