The calcium citrate is the calcium salt of ‘ citric acid ; It is widely used in the food sector as a synergistic antioxidant additive (E333), exploiting at the same time its acidity correcting and flavor enhancing properties ( orange candies, sugared almonds, chewingum, fruit and fruit juices ). Reading between the lines of the nutritional labels, this additive is also common in cheeses and in many frozen baked goods.
Calcium citrate is known to be an important and widespread supplement of calcium , a mineral essential for the good health of bones , teeth , but also of the entire body. For the same purpose it can be added to so-called fortified foods , then artificially enriched with this and possibly other nutrients .
Each gram of calcium citrate contains about 210 milligrams of elemental calcium, just over half of that contained in one gram of calcium carbonate . These two salts are the most common sources of calcium in supplements and dietary products intended for supplementing the mineral, often enriched with vitamin D to promote its absorption . Since this becomes optimal in an acidic environment, calcium citrate is indicated for people suffering from hypochlorhydria and can also be taken on an empty stomach. Conversely, people suffering from stomach acidthey 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 a fruit juice or citrus juice , natural sources of citric acid also containing small quantities 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 lower, to 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 ] there is talk of a better absorption of calcium citrate than calcium carbonate. However, considering the much higher cost of citric acid salt, the cost-effectiveness ratio is clearly in favor of calcium carbonate in healthy subjects [ 3 ] . On the basis of the literature consulted, in the subject in good health, calcium carbonate taken in conjunction with meals represents the most cost-effective supplementary form. Conversely, calcium citrate is to be preferred in case of hypochlorhydria, in turn linked to the use of drugs against gastritis , peptic ulcer orgastroesophageal reflux , such as proton pump inhibitors and histamine H2 receptor antagonists [ 6 ] . The same goes for patients undergoing gastric bypass surgery, in which calcium citrate is preferable to carbonate [ 7 ] .
Side effects and advice for use
Regardless of the calcium source chosen, remember that the percentage of mineral absorbed depends in the first instance on the dose: it is maximum for supplies of less than 500 mg and tends to decrease for higher supplies. Therefore, in the event that the doctor recommends supplementing with 1000 mg of calcium per day, it may be useful to divide the dose into two different daily intakes 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 previously discussed with your doctor, especially in the presence of diseases or simultaneous intake of drugs or other supplements. Conditions such as kidney stones , hyperparathyroidism and concomitant antacid therapy, digoxin or tetracycline antibiotics ( tetracycline , demeclocycline, doxycycline , minocycline or oxytetracycline), could in fact make them contraindicated or require dose adjustment.
Side effects of calcium citrate, in addition to increased gastric acidity in predisposed individuals, can include minor intestinal disorders such as bloating, nausea , and constipation .
Calcium citrate and kidney stones
The relationship between calcium supplement intake and kidney stone risk is still uncertain, given the conflicting epidemiological evidence, with studies even attributing a protective effect to calcium supplementation. In any case, 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 against the disease. It probably refers to the known alkalizing effect of the urine exerted by citric acid; however, please note that increasing the urinary pH reduces the risk of cystine, xanthine and uric acid stones, but increases the likelihood of calcium phosphate kidney concretions formingcalcium carbonate , magnesium phosphate and struvite  . So, in the presence of kidney stones, it is very important to consult a doctor before taking calcium citrate supplements.