Calcium hydrogen carbonate
The dissolved form of chalk, found naturally in hard water. Used in food and beverages to regulate acidity and add calcium.
What is it?
Calcium hydrogen carbonate (also called calcium bicarbonate, formula Ca(HCO3)2) is the dissolved form of calcium carbonate. Unlike chalk or limestone, it cannot exist as a stable solid: it only occurs in aqueous solution, where calcium ions and bicarbonate ions coexist in equilibrium with dissolved carbon dioxide. Hard tap water and many mineral waters contain it naturally. In the food additive numbering system it was historically labelled E170(ii), sometimes written E170b, and in older UK regulations was listed alongside E170(i) calcium carbonate under a shared E170 heading.
What does it do?
In solution, calcium hydrogen carbonate acts as an acidity regulator: the bicarbonate ions neutralise excess acid and buffer pH. It can also provide a source of dietary calcium in beverages. Because it decomposes on heating, releasing carbon dioxide and reverting to calcium carbonate, it can contribute to leavening in some baked applications. In water treatment it is used to remineralise soft or desalinated water before bottling.
Where you will see it
Primarily used in the beverage and water industry, including bottled mineral water remineralisation and some soft drinks. Can appear in bakery products and calcium-fortified foods. On a UK ingredient label it may be declared as 'E170', 'calcium carbonate', or 'acidity regulator (E170)'.
What the science says
Regulatory status and the 2005 UK reclassification
Under UK and EU food law, E170 covers calcium carbonates as a group. The UK Miscellaneous Food Additives (Amendment) (England) Regulations 2005 explicitly merged the two historical sub-entries, E170(i) calcium carbonate and E170(ii) calcium hydrogen carbonate, into a single listing: 'Calcium carbonate'. Calcium hydrogen carbonate therefore no longer holds a separate regulatory code in UK law but is covered under E170. It is authorised under assimilated EU Regulation 1333/2008 and in many food categories at quantum satis (no fixed upper limit).
The UK 2005 amendment substituted the two-part entry 'Calcium carbonates (i) calcium carbonate (ii) calcium hydrogen carbonate' with simply 'Calcium carbonate', consolidating both forms under E170.
E170 is listed as authorised for Great Britain under assimilated Regulation (EC) No 1333/2008 Annex II, effective from 31 December 2020.
EFSA safety re-evaluations of E170
EFSA reviewed calcium carbonate (E170) in 2011 and again in 2023. Both reviews concluded there is no need for a numerical acceptable daily intake, and no safety concern from calcium carbonate itself at the use levels found in food. The 2023 opinion noted that calcium hydrogen carbonate is not separately addressed in these evaluations, as it is treated as part of the same E170 group.
The EFSA Panel concluded there is no need for a numerical ADI for calcium carbonate and no safety concern with respect to exposure to calcium carbonate per se at currently reported use levels, including for infants below 16 weeks.
The earlier 2011 EFSA re-evaluation assigned 'ADI not specified', reflecting no toxicological concern for the calcium carbonate compound itself at food additive use levels.
Aluminium as an unavoidable impurity in E170
Calcium carbonate is a mineral product and naturally contains trace impurities including aluminium, originating from clay in limestone. EFSA's 2023 opinion flagged this specifically: the aluminium present in commercially available E170 could, at the highest measured concentrations, exceed the tolerable weekly intake for aluminium many times over when dietary exposure from all sources is combined. EFSA recommended new maximum limits for aluminium in E170 specifications. This concern applies to the parent compound E170, not to calcium hydrogen carbonate as a distinct substance. Because calcium hydrogen carbonate exists only in dilute aqueous solution and is used at relatively low concentrations, its contribution to aluminium exposure would be lower than solid calcium carbonate uses.
EFSA found that the unavoidable presence of aluminium in E170 is of concern. At the highest measured values in commercial calcium carbonate (1,120 mg aluminium per kg), the tolerable weekly intake for aluminium could be exceeded by approximately 890% when combined with other dietary sources.
EFSA recommended new specification limits for aluminium, lead, cadmium, arsenic, and mercury in E170, noting that decontamination of aluminium from calcium carbonate at industrial scale is not currently available.
Chemical instability and practical food use
Calcium hydrogen carbonate cannot be isolated as a dry powder: heating or evaporation causes it to decompose into calcium carbonate, carbon dioxide, and water. This limits its practical application to liquid or aqueous food systems. It is not used as a standalone additive in the same way as solid calcium carbonate and is most commonly encountered as a naturally occurring component of hard water used in food and drink production.
Calcium hydrogen carbonate exists only in aqueous solution and decomposes on heating or evaporation to yield calcium carbonate, carbon dioxide, and water. It cannot be produced or stored as a stable solid.
Where it stands with the regulators
Who should be careful
People managing hypercalcaemia or a history of calcium-containing kidney stones should monitor total calcium intake from all sources, including calcium-fortified foods. On a label, look for 'E170', 'calcium carbonate', or 'acidity regulator (E170)'.
The honest read
Calcium hydrogen carbonate is one of the most ordinary substances in food: it is the mineral dissolved in hard tap water and in most natural mineral waters. As a deliberately added food ingredient it has decades of regulatory review behind it, no IARC classification, no ban, and no reproductive or endocrine concern. The only regulatory flag raised in recent years concerns aluminium as a geogenic impurity in solid calcium carbonate products, not a biological property of the carbonate itself. EFSA has asked manufacturers to tighten specification limits for aluminium in E170 products, and that work is ongoing.
Related additives
Common questions
Is E170b banned in the UK?
No. Calcium hydrogen carbonate (historically E170ii or E170b) is authorised in the UK under the broader E170 designation, which covers calcium carbonates. A 2005 UK regulation merged the two sub-entries into a single listing.
Is E170b the same as E170?
Effectively yes. The designation E170b (or E170ii) referred specifically to calcium hydrogen carbonate, the dissolved bicarbonate form. UK and EU law now treats it as part of the single E170 entry. On food labels you will see E170 or 'calcium carbonate', not E170b separately.
What foods contain E170b?
Calcium hydrogen carbonate is found naturally in hard water and most mineral waters. As a deliberate additive it appears mainly in beverages, calcium-fortified plant milks and juices, and bakery products. On labels it will appear as E170 or 'calcium carbonate'.
Is E170b vegan?
Yes. Calcium carbonate and calcium hydrogen carbonate are mineral-derived and contain no animal products. They are suitable for vegans and vegetarians.
Sources
- UK FSA Regulated Products database, E-170 Calcium carbonate
- The Miscellaneous Food Additives (Amendment) (England) Regulations 2005, SI 2005/1099
- EFSA Panel on Food Additives and Flavourings (2023): Re-evaluation of calcium carbonate (E 170) as a food additive, EFSA Journal 2023;21(7):8106
- EFSA ANS Panel (2011): Scientific Opinion on re-evaluation of calcium carbonate (E 170) as a food additive, EFSA Journal 2011;9(6):2318
- UK Food Standards Agency: Approved additives and E numbers
- Wikipedia: Calcium bicarbonate
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