Absorbability and cost effectiveness in calcium supplementation

Background: Cost-effectiveness of calcium supplementation depends not only on the cost of the product but on the efficiency of its absorption. Publish ed cost-benefit analyses assume equal bioavailability for all calcium sourc es. Some published studies have suggested that there are differences in bot h the bioavailability and cost of the major calcium supplements. Design: Randomized four period, three-way cross-over comparing single doses of off-the-shelf commercial calcium supplements containing either calcium carbonate or calcium citrate compared with a no-load blank and with encapsu lated calcium carbonate devoid of other ingredients; subjects rendered full y vitamin D-replete with 10 mug/day 25(OH)D by mouth, starting one week pri or to the first test. Subjects: 24 postmenopausal women. Methods: Pharmacokinetic analysis of the increment in serum total and ioniz ed calcium and the decrement in serum iPTH induced by an oral calcium load, based upon multiple blood samples over a 24-hour period; measurement of th e rise in urine calcium excretion. Data analyzed by repeated measures ANOVA . Cost calculations based on average retail prices of marketed products use d in this study from April through October, 2000. Results: All three calcium sources (marketed calcium carbonate, encapsulate d calcium carbonate and marketed calcium citrate) produced identical 24-hou r time courses for the increment in total serum calcium. Thus, these were e qually absorbed and had equivalent bioavailability. Urine calcium rose slig htly more with the citrate than with the carbonate preparations, but the di fference was not significant. Serum iPTH showed the expected depression acc ompanying the rise in serum calcium, and there were no significant differen ces between products. Conclusion: Given the equivalent bioavailability of the two marketed produc ts, the cost benefit analysis favors the less expensive carbonate product.