Calcium and Bioavailability
Bioavailability is widely considered to be the rate and extent that active substances are absorbed and become available for utilisatoin at the site of action in the body.
The
bioavailability of calcium supplements is therefore often determined by comparing relative perfomances in solubility and absorbtion trials.
Although different forms of calcium are able to be ranked in terms of their solubility and in some cases their absorbability, this information doesn't reliably reflect the actual efficacy of the product, and should not be used as a comparison between different types of calcium.
What is of primary importance is the therapeutic effect of the calcium supplement. It is Waitaki's view that bioavailability is best judged by the ability of the supplement to positively influence bone mineral density or bone healing, regardless of the level of solubility or absorbability.
Ruegsegger et al (Osteoporosis Intl, 1995) proved this point by comparing
ossein-hydroxyapatite (whole bone extract) and calcium carbonate at the same daily dose of 1400 mg calcium / day in osteoporotic females. At the conclusion of the trial the ossein-hydroxyapatite was significantly more effective than the calcium carbonate at increasing bone mineral density - even though calcium carbonate is considered the more soluble of the two.
The
Ruegsegger study confirmed the fact that
ossein-hydroxyapatite is a form of calcium that is better utilised by the body (and therefore more bioavailable) than calcium carbonate.
Similarly, Epstein et al (The American Journal of Clinical Nutrition, 1982) demonstrated that ossien hydroxyapatite improved cortical bone thickness in a group of women by 11.6%, compared to an improvement of only 7% in those supplemented with caclium gluconate. .