Calcium carbonate
Ground limestone added to food as a white colouring, calcium fortifier, and acidity regulator. Mandatory in UK white flour since 1942.
Calcium carbonate itself raises no concern at food additive levels, but it can carry aluminium as a natural impurity. EFSA found that calcium carbonate used in food could contribute 50 to 100% of the weekly aluminium exposure limit, with some batches exceeding it by up to four times.
What is it?
Calcium carbonate is the mineral that makes up chalk, limestone, and marble. Food-grade E170a is produced by grinding limestone rock into a fine white powder. A synthetically precipitated form also exists. The formula is CaCO3.
What does it do?
As a colour it provides whiteness to icings and confectionery coatings. As an acidity regulator it neutralises excess acid in food systems. As a calcium source it raises the calcium content of fortified foods. In flour it releases carbon dioxide on contact with acid, which can assist leavening. It also acts as an anti-caking agent in powdered products.
Where you will see it
White bread and all non-wholemeal flour sold in the UK (required by law since 1942), white icing and cake decorations, chewing gum, plant-based milks such as oat, soy and almond drinks, fortified breakfast cereals, infant formula, antacid tablets, and some powdered soft drink mixes. On the label it appears as E170 or calcium carbonate.
What the science says
Aluminium contamination in the additive
Calcium carbonate extracted from limestone contains naturally occurring aluminium that cannot be fully removed during processing. EFSA's 2023 re-evaluation found that, at the specification limits proposed by industry, the aluminium carried in calcium carbonate used as a food additive could contribute 50 to 100% of the established aluminium tolerable weekly intake (TWI) on its own. In the highest-contamination batches tested, the TWI could be exceeded by up to four times, and at the single highest measured aluminium value (1,120mg/kg), exceedance reached up to 890% of the TWI. EFSA recommended introducing a maximum limit for aluminium in E170 specifications, which had not previously existed.
Aluminium intake from calcium carbonate used as a food additive could account for 50 to 100% of the EFSA tolerable weekly intake for aluminium of 1mg per kilogram of body weight per week.
At industry-proposed specification limits for aluminium in E170, the aluminium TWI could be exceeded by up to approximately four times; at the highest measured aluminium level in precipitated calcium carbonate (1,120mg/kg), exceedance reached up to 890% of the TWI.
EFSA recommended lowering maximum limits for lead, cadmium and arsenic in E170 and introducing new maximum limits for mercury and aluminium, as no aluminium limit had previously been set in the EU specifications.
EFSA's conclusion on calcium carbonate itself
Separate from the aluminium contamination issue, EFSA concluded that calcium carbonate as a compound raises no safety concern at the use levels currently permitted in food, including in infant formula for babies under 16 weeks old. The panel set no numerical acceptable daily intake for calcium carbonate itself. Dietary exposure from E170 in food represents only a fraction of total calcium intake, well below the levels at which calcium itself causes harm.
There is no safety concern with respect to calcium carbonate per se at currently reported use levels in all age groups, including infants below 16 weeks of age.
No numerical ADI is required for calcium carbonate; JECFA has held an ADI of 'not limited' for calcium carbonate since 1965.
Aluminium in food: established toxicity concern
Aluminium is not an inert contaminant. EFSA identified developmental toxicity, effects on the urinary tract, and neurotoxicity as known effects of aluminium and its compounds, and set the TWI of 1mg/kg body weight per week on this basis. Average dietary aluminium exposure in European populations runs at roughly 50% of the TWI; certain groups, including infants on formula and young children on specialist diets, can exceed it. The 2008 EFSA opinion did not find evidence that dietary aluminium causes Alzheimer's disease, but noted that the overall database had limitations.
EFSA established a tolerable weekly intake of 1mg aluminium per kilogram of body weight per week, based on developmental toxicity, urinary tract effects, and neurotoxicity.
Mean weekly aluminium exposure from food in European populations averages around 50% of the TWI; infants on formula and young children on specialist diets can exceed the TWI.
High-dose calcium: milk-alkali syndrome and kidney concerns
At supplement or antacid doses, calcium carbonate can cause milk-alkali syndrome, a triad of high blood calcium, metabolic alkalosis, and acute kidney injury. This is a dose-dependent effect at levels far above those from food additives. Published case reports and clinical reviews confirm milk-alkali syndrome is now one of the most common causes of high blood calcium in adults, primarily from supplement and antacid overuse. Food additive levels of calcium carbonate do not approach the thresholds that trigger these effects.
Milk-alkali syndrome, characterised by hypercalcaemia, metabolic alkalosis and acute kidney injury, is primarily caused by excessive intake of calcium carbonate as a supplement or antacid, not by food additive levels.
Long-term calcium carbonate supplement use of over 2g per day can lead to hypercalcaemia, renal calculi, hypophosphataemia, and nephrotoxicity.
Where it stands with the regulators
Who should be careful
No specific population group needs to avoid E170 at food additive levels. People taking calcium carbonate as a supplement or antacid at high doses should follow medical guidance, as supplemental doses carry risks not applicable to food additive exposure. Vegans who want to confirm the source of their calcium carbonate should check with the manufacturer. EU and UK specifications for food-grade E170 define it as obtained by grinding limestone or by precipitation, making geological or synthetic origin the norm for E170-labelled food additives. However, the plain label term 'calcium carbonate' (without the E number) can describe products derived from oyster shells or eggshells, so checking with the manufacturer is worthwhile when vegan status matters. On the label, look for E170 or calcium carbonate.
The honest read
Calcium carbonate itself is one of the most thoroughly reviewed food additives, and EFSA's most recent opinion, published in 2023, found nothing concerning about the compound at the levels used in food. The genuine open question is not about calcium carbonate but about aluminium carried as an impurity in the mined mineral. EFSA found that this contamination could, in some cases, push a person's aluminium exposure significantly above the weekly limit regulators have set, without any maximum aluminium limit currently existing in EU specifications for E170. Regulators recommended introducing one. Until that specification change is made and enforced, the aluminium load in any given batch of calcium carbonate used in food is not formally capped. That is a live regulatory gap, not a settled matter.
Related additives
Common questions
Is E170a banned in the UK?
No. Calcium carbonate (E170) is approved for use in UK and EU food under assimilated EU Regulation 1333/2008 and is also mandated by law in non-wholemeal wheat flour under the Bread and Flour Regulations 1998.
Why is there a concern flag if EFSA says calcium carbonate itself is fine?
The concern relates to aluminium contamination, not the calcium carbonate molecule itself. EFSA's 2023 review found that E170, as mined from limestone, contains aluminium that cannot be fully removed. At the levels found in some batches, it could contribute 50 to 100% of the tolerable weekly intake for aluminium, with high-contamination samples exceeding the limit by up to four times. EFSA recommended setting a new maximum aluminium limit for E170, which had not previously existed.
What foods contain E170a?
All non-wholemeal white bread and flour sold in the UK contains it by law. It also appears in white cake icings and decorations, chewing gum, plant-based milks such as oat drink and soy milk, fortified breakfast cereals, and some infant formula products.
Is E170a vegan?
For the food additive E170 specifically, yes in practice. EU and UK specifications define food-grade E170 as obtained by grinding limestone or by precipitation, both non-animal processes. If a product lists 'E170' or 'calcium carbonate (E170)', the additive-grade form is the expected source. Plain 'calcium carbonate' without an E number can be derived from oyster shells or eggshells in some supplement products, so if you are in any doubt, contact the manufacturer directly.
Sources
- EFSA Panel on Food Additives and Flavourings (FAF): Re-evaluation of calcium carbonate (E 170) as a food additive in foods for infants below 16 weeks of age and follow-up of its re-evaluation as food additive for uses in foods for all population groups. EFSA Journal 2023;21(7):8106
- PMC full text: Re-evaluation of calcium carbonate (E 170) EFSA 2023
- UK FSA Approved additives and E numbers
- UK FSA Regulated Products Database: E170
- EFSA: Safety of aluminium from dietary intake. EFSA Journal 2008;754
- StatPearls: Calcium Carbonate. NCBI Bookshelf NBK562303
- Real Bread Campaign / Sustain: Flour fortification chalk supply presents a risk to the UK food system (December 2024)
- Bread and Flour Regulations 1998 (UK legislation)
- International Association of Color Manufacturers: Calcium Carbonate colour profile
- VeganFriendly.org.uk: Is calcium carbonate vegan?
- Commission Regulation (EU) No 231/2012 laying down specifications for food additives (Annex, Division 42: Calcium carbonate)
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