Impact of Gastric pH and Dietary Fiber on Calcium Availability of Various Calcium Salts

The objective of this study was to compare calcium release and ionization from commercial calcium supplements and various salts of calcium with different solubilities. The impact of pH of test fluid and dietary fiber co-administered with calcium supplement on calcium availability was also studied. Compressed tablets of six different calcium salts were prepared by direct compression. Calcium release from tablets was tested in simulated gastric fluid without pepsin (SGF, pH 1.2) or fed state simulated gastric fluid (FSSGF, pH 4.8), using USP dissolution apparatus. The ionized calcium concentration in test fluid was determined by calcium ion selective electrode. The results demonstrated that most of the formulations released calcium within 1 hour. Tablets made of higher solubility calcium salts demonstrated a faster calcium release. The calcium release from calcium hydrogen phosphate and calcium carbonate tablets in gastric fluid with higher pH showed a slower calcium release than in SGF. The dietary fiber co-administered with calcium supplement influenced the calcium availability, especially in medium with higher pH. The results suggested that most of the calcium salts could be used as calcium supplement. However, the use of calcium carbonate required an acidic environment in order to be dissolved in the gastrointestinal tract.