The amount of calcium absorbed from calcium citrate supplements is consistently higher than the amount absorbed from calcium carbonate supplements. This difference is important because women who take calcium supplements that are poorly absorbed are not as well protected against calcium-related bone loss and possible osteoporosis. The researchers pooled data from 15 previously published studies in which men and women took either calcium citrate or calcium carbonate supplements. Calcium citrate is better absorbed than calcium carbonate by about 25%, whether it is taken on an empty stomach or given with meals.
American Journal of Therapeutics November 1999;6:303-311,313-321.
Journal of Clinical Pharmacology December 1999;39:1-4.