This is a randomized, double-blind, crossover bioavailability study comparing the fractional absorption of calcium from amorphous calcium carbonate (ACC) versus crystalline calcium carbonate (CCC) using stable calcium isotopes in postmenopausal women.~The study is comprised of 15 subjects orally administered immediately after breakfast a 600 mg gelatin capsules containing either 600 mg (2 capsules of 300 mg)of ACC (192 mg elemental calcium) of 480 mg CCC (192 mg elemental calcium), labeled with 15 mg of 44Ca (2 capsules of 300 mg).~Five minutes following the oral administration, each subject will be infused intravenously with 1.5 mg of CaCl2 labeled with 42Ca over 10 min. Over the following 24 h subjects will consume meals that will be selected by the Unit of Clinical Nutrition at Sourasky Medical Center nutritionist on the basis of their food diary and ALL urine excreted during this time should be collected in a designated urine container and returned to the Unit of Clinical Nutrition at Sourasky Medical Center for evaluation. The same protocol as in day 0 with a crossover oral treatment will be performed after 21 day washout period.~Dosing day will be designated Day 0. Eligible subjects are randomly assigned to one of the study treatments according to the following regimens:
The study objective is, to evaluate the fractional absorption of calcium from amorphous calcium carbonate (ACC) Vs crystalline calcium carbonate (CCC) dietary supplements in postmenopausal women.