Calcium citrate is the
calcium salt
Although most compounds are referred to by their IUPAC systematic names (following IUPAC nomenclature), traditional names have also been kept where they are in wide use or of significant historical interests.
A
Ac
* Actinium(III) chlorid ...
of
citric acid
Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2. It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in ...
. It is commonly used as a
food additive (
E333), usually as a
preservative
A preservative is a substance or a chemical that is added to products such as food products, beverages, pharmaceutical drugs, paints, biological samples, cosmetics, wood, and many other products to prevent decomposition by microbial growth or by ...
, but sometimes for
flavor. In this sense, it is similar to
sodium citrate Sodium citrate may refer to any of the sodium salts of citric acid (though most commonly the third):
* Monosodium citrate
* Disodium citrate
* Trisodium citrate
The three forms of salt are collectively known by the E number E331.
Applications ...
. Calcium citrate is also found in some dietary calcium supplements (e.g.
Citracal or
Caltrate). Calcium makes up 24.1% of calcium citrate (anhydrous) and 21.1% of calcium citrate (tetrahydrate) by mass. The tetrahydrate occurs in nature as the mineral
Earlandite.
In 2020,
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
was the 204th most commonly prescribed medication in the United States, with more than 2million prescriptions.
Chemical properties
Calcium citrate is sparingly soluble in water. Needle-shaped crystals of tricalcium dicitrate tetrahydrate
a3(C6H5O7)2(H2O)2·2H
2O were obtained by hydrothermal synthesis. The crystal structure comprises a three-dimensional network in which eightfold coordinated Ca
2+ cations are linked by citrate anions and hydrogen bonds between two non-coordinating crystal water molecules and two coordinating water molecules.
[
]
Production
Calcium citrate is an intermediate in the isolation of
citric acid
Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2. It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in ...
from the fungal
fermentation process by which citric acid is produced industrially. The citric acid in the broth solution is neutralized by
limewater, precipitating insoluble calcium citrate. This is then filtered off from the rest of the broth and washed to give clean calcium citrate.
: 3 Ca(OH)
2(s) + 2 C
6H
8O
7(l) → Ca
3(C
6H
5O
7)
2(s) + 6 H
2O
(l)
The calcium citrate thus produced may be sold as-is, or it may be converted to citric acid using dilute sulfuric acid.
Biological role
In many individuals,
bioavailability
In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation.
By definition, when a medication is administered intravenously, its bioavailability is 100%. Ho ...
of calcium citrate is found to be equal to that of the cheaper
calcium carbonate. However, alterations to the digestive tract may change how calcium is digested and absorbed. Unlike calcium carbonate, which is basic and neutralizes stomach acid, calcium citrate has no effect on stomach acid.
Calcium carbonate is harder to digest than calcium citrate, and calcium carbonate carries a risk of "acid rebound" (the stomach overcompensates by producing more acid), so individuals who are sensitive to antacids or who have difficulty producing adequate stomach acid may choose calcium citrate over calcium carbonate for supplementation. According to recent research into calcium absorption after gastric bypass surgery,
[
] calcium citrate may have improved bioavailability over calcium carbonate in Roux-en-Y gastric bypass patients who are taking calcium citrate as a
dietary supplement after surgery. This is mainly due to the changes related to where calcium absorption occurs in the digestive tract of these individuals.
References
External links
National Cancer Institute
{{DEFAULTSORT:Calcium Citrate
Citrates
Calcium compounds
E-number additives