Calcium citrate is the calcium salt of citric acid; it is widely used in the food field as a synergistic antioxidant additive (E333), at the same time exploiting the corrective properties of acidity and flavor enhancers (orange candies, sugared almonds, chewingum, fruit and fruit juices). Reading between the lines of nutritional labels, this additive is also commonly found in cheeses and in many frozen bakery products.
Each gram of calcium citrate contains about 210 milligrams of elemental calcium, just over half that contained in a gram of calcium carbonate. These two salts represent the most common sources of calcium in supplements and in dietary products intended for the integration of the mineral, often enriched with vitamin D to favor absorption. Since this becomes optimal in an acid environment, calcium citrate is indicated for people suffering from hypochloridria and can also be taken on an empty stomach. Conversely, people suffering from stomach acidity should prefer calcium carbonate, to be taken in conjunction with meals; alternatively, calcium carbonate can also be taken on an empty stomach in association with fruit juice or citrus juice, natural sources of citric acid that also contain small amounts of calcium citrate.
Bioavailability (absorption) of Calcium citrate
The carbonate salt has the advantage of convenience and in healthy people its absorption is practically identical, or only slightly less, than that of calcium citrate.
Despite what has been stated, often for purely commercial purposes, various studies [1, 2, 3] underline the absence of significant differences in terms of absorption and bioavailability of calcium citrate and calcium carbonate in healthy people.
In some documents [4, 5] we talk about a better absorption of calcium citrate compared to calcium carbonate. However, given the much greater cost of citric acid salt, in healthy subjects the cost-effectiveness ratio is clearly in favor of calcium carbonate [3]. On the basis of the literature consulted, in the subject in good health, the calcium carbonate taken in conjunction with meals represents the most effective supplementary form in terms of costs. Conversely, calcium citrate is preferable in the case of hypochloridria, in turn linked to the use of drugs against gastritis, peptic ulcer or gastroesophageal reflux, such as proton pump inhibitors and histamine H2 receptor antagonists [6 ]. The same applies to patients undergoing gastric bypass surgery, in which calcium citrate is preferable to carbonate [7].
Side effects and advice for use
Regardless of the source of calcium chosen, let us remember that the percentage of mineral absorbed depends in the first instance on the dose: it is maximum for inputs less than 500 mg and tends to decrease for higher inputs. Therefore, if the doctor recommends supplementing with 1000 mg of calcium per day, it could be useful to divide the dose into two different daily intake of 500 mg (a choice that must obviously be discussed with the doctor himself). In fact, we remind you that the use of calcium-based supplements should be discussed in advance with your doctor, especially in the presence of diseases or the simultaneous intake of drugs or other supplements. Conditions such as kidney stones, hyperparathyroidism and concomitant therapy with antacids, digoxin or tetracycline antibiotics (tetracycline, demeclocicline, doxycycline, minocycline or oxytetracycline) may indeed make them contraindicated or require dose adjustment.
The side effects of calcium citrate, in addition to an increase in gastric acidity in predisposed individuals, may include small bowel disorders such as bloating, nausea, and constipation.
Calcium citrate and kidney stones
The relationship between the intake of calcium supplements and the risk of kidney stones is still uncertain, given the contrasting epidemiological evidence, with studies that even attribute a protective effect to calcium supplementation. However, one of the benefits classically ascribed to calcium citrate is the lower tendency to form kidney stones, while for commercial purposes it is even attributed a preventive role towards the disease. Probably reference is made to the known alkalizing effect of urine exerted by citric acid; it should be remembered, however, that increasing the urinary pH reduces the risk of cystine, xanthine and uric acid stones, but increases the likelihood of the formation of renal concretions of calcium phosphate, calcium carbonate, magnesium phosphate and struvite [8]. Therefore, in the presence of kidney stones, it is very important to consult a doctor before taking calcium citrate supplements.
Bibliography
1. Heaney RP, Dowell MS, Barger-Lux MJ. Absorption of calcium as the carbonate and citrate salts, with some observations on method. Osteoporos Int 9: 19–23, 1999
2. Chrischilles EA. Public health implications of interventions to promote calcium intake: cost-benefit considerations. Paper presented to the NIH Consensus Development Conference on Optimal Calcium Intake, June 1994, Washington, DC.
3. Heaney RP, Dowell MS, Bierman J, Hale CA, Bendich A (June 2001). "Absorbability and cost effectiveness in calcium supplementation". Journal of the American College of Nutrition 20 (3): 239–46.
4. Heller HJ, Stewart A, Haynes S, Pak CYC: Pharmacokinetics of calcium absorption from two commercial calcium supplements. J Clin Pharmacol 39: 1151–1154, 1999.
5. Sakhaee K, Bhuket T, Adams-Huet B, Rao DS. Meta-analysis of calcium bioavailability: a comparison of calcium citrate with calcium carbonate. Am J Ther. 1999 Nov; 6 (6): 313-21.
6. Straub DA. Calcium supplementation in clinical practice: a review of forms, doses, and indications. Nutr Clin Pract. 2007 Jun; 22 (3): 286-96.
7. ondapu, P. and Provost, D. and Adams-Huet, B. and Sims, T. and Chang, C. and Sakhaee, K. (June 2009). "Comparison of the Absorption of Calcium Carbonate and Calcium Citrate after Roux-en-Y Gastric Bypass". Obesity Surgery 19 (9): 1256–1261.
8. Wagner CA, Mohebbi N. "Urinary pH and stone formation." J Nephrol. 2010 Nov-Dec; 23 Suppl 16: S165-9.
