OS-CAL (Calcium Carbonate) or Calcium Citrate?
The absorption myths
Gastric acidity impacts absorption — False
Gastric acidity has no impact. Gastric acid secretion was believed to play a critical role in calcium absorption; however, research does not bear this out.
A study of calcium absorption in patients with achlorhydria showed that calcium carbonate supplements had completely normal absorption when taken following a meal, even in achlorhydric patients.1,2
A study of the role of gastric acid in calcium absorption demonstrated that a large dose of cimetidine (an H2 receptor antagonist), which markedly reduced gastric acid secretion, did not alter calcium absorption in normal subjects. Moreover, calcium absorption after calcium carbonate ingestion was the same when intragastric contents were maintained at pH 7.4 as when intragastric pH was 3.0.2
"Contrary to popular belief, calcium carbonate and calcium citrate are equally well absorbed if taken with meals, the normal way of assimilating any nutrient."
North American Menopause Society Position Statement 20063
Solubility helps to guarantee absorption — False
Solubility does not guarantee absorption. Calcium citrate (Citracal®) is more soluble in water than calcium carbonate (OS-CAL), but that does not mean it is absorbed more readily in the body.
Comparative pharmacokinetic studies using urine and serum tracer methods demonstrated that when supplements were taken with food, calcium carbonate absorption was unsurpassed. Equivalent absorption results were seen in both high- (1000 mg) and low-dose (300 mg) formulation comparisons.4
A 2001 study that compared calcium carbonate (OS-CAL) and calcium citrate (Citracal®) showed that these supplements exhibited identical bioavailability values. Because OS-CAL is less expensive than Citracal®, yet exhibited equivalent bioavailability, OS-CAL is the most economical choice of the two per unit of absorbed calcium.5
OS-CAL for Unsurpassed Calcium Absorption