Meta-analysis of calcium bioavailability: a comparison of calcium citrate with calcium carbonate

Am J Ther. 1999 Nov;6(6):313-21. doi: 10.1097/00045391-199911000-00005.


Objective: To perform a meta-analysis of data from available published trials comparing the bioavailability of calcium carbonate with that of calcium citrate.

Data sources: The whole set was comprised of 15 studies involving 184 subjects who underwent measurement of calcium absorption from calcium carbonate and calcium citrate. Category A excluded four studies for lack of physiological relevance, use of a mixed preparation with low content of calcium carbonate, or wide variability in results. Category B was comprised of five studies (from Category A) involving 71 subjects who took calcium supplements on an empty stomach. Category C was comprised of six studies (from Category A) involving 65 subjects who took calcium preparations with meals.

Method: The meta-analysis of calcium absorption data from calcium carbonate and calcium citrate, with calculation of effect size and 95% confidence intervals.

Results: Calcium absorption from calcium citrate was consistently significantly higher than that from calcium carbonate by 20.0% in the whole set, by 24.0% in Category A, by 27.2% on an empty stomach, and by 21.6% with meals.

Conclusion: Calcium citrate is better absorbed than calcium carbonate by approximately 22% to 27%, either on an empty stomach or co-administered with meals.

Publication types

  • Comparative Study
  • Meta-Analysis
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Biological Availability
  • Calcium Carbonate / pharmacokinetics*
  • Calcium Citrate / pharmacokinetics*
  • Calcium, Dietary*
  • Humans


  • Calcium, Dietary
  • Calcium Carbonate
  • Calcium Citrate