Calcium Carbonate
Calcium Carbonate is a tier 2 form of Calcium, used in 2,482 on-market products and providing 40.0% elemental calcium by weight.
2,482
on-market products
tier 2
quality tier
40.0%
elemental fraction
Basis: CaCO3, anhydrous (no commercial hydrate exists)
Why this tier: Absorption consistently ~20-27% lower than citrate in a meta-analysis; requires stomach acid/food co-administration for optimal absorption.
Source: Sakhaee K et al. 1999, Am J Ther 6(6):313-321, PMID 11329115