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Oscal (Os-cal) Review

Oscal  is a calcium carbonate dietary supplement and registered trademark of GlaxoSmithKline. Oscal | ArticleOscal, whose name some people believe comes from oyster shell calcium, appears to comprised at least partly, of powdered oyster shell calcium.

Comparing Oscal, Citracal, and Calcium Carbonate
As a long established brand, Oscal has been used in many clinical trials.  In a 2001 Journal of Nutrition article entitled “Absorbability and Cost Effectiveness in Calcium Supplementation,” Heaney noted that  Oscal, Citracal,  and  a precipitate calcium carbonate were equally absorbed using multiple absorption models:

“Table I presents the pharmacokinetic parameters for both total and ionized serum calcium for the four test sources, and Fig. 1 and 2 show the time courses of total and ionized calcium, respectively. The AUC values for the three calcium sources were all highly significantly different from the blank (p < 0.001), but there was no significant difference between the three calcium-containing sources for either of the AUC values or any of the other pharmacokinetic parameters. Also, as Fig. 1 shows graphically, the three sources produced virtually identical total serum calcium time courses, whether expressed as absolute values (Fig. 1A) or as increment above baseline (Fig. 1B).

Serum calcium values differed significantly from the corresponding values following the blank load at all time points from 3 to 12 hours for Os-Cal® and from 1 to 9 hours for Citracal®, but there were no significant differences between the calcium sources at any time point. Fig. 2B shows that the incremental elevation of serum ionized calcium for the citrate source was somewhat greater from 5 to 12 hours compared to Os-Cal and from 5 to 9 hours compared to the plain calcium carbonate. Consistent with this difference, the AUC24 for ionized calcium (Table 1) was greater for the citrate than for the carbonate preparations. However, given the dispersion of the individual AUC data, none of these differences was statistically significant. There was no effect of the order of the test substance on any of the outcome variables. Similarly, age and estrogen status were also tested and were without effect on the relative absorbabilities of the test calcium sources.”

A second comparison was run by Heaney et al, published in 2003, and revealed similar results to the first test.

The same chemical form of calcium in Oscal, calcium carbonate, has been tested against AdvaCAL in multiple studies. Among those published studies, AdvaCAL participants typically reported statistically significant bone benefits; the calcium carbonate users did not.

Oscal + Vitamin D versus a Placebo
The Women’s Health Initiative was a large study, published in the New England Journal of Medicine in 2006.  This 7-year study tracked bone density changes and hip fracture risk among 36,000 women taking Oscal plus vitamin D or a placebo. The authors concluded:

“Among healthy postmenopausal women, [Oscal+D] supplementation resulted in a small but significant improvement in hip bone density, did not significantly reduce hip fracture, and increased the risk of kidney stones.”

Oscal | ArticleAverage bone density was 1% higher for patients taking the Oscal with vitamin D versus placebo after 7 years.  A sub analysis of highly compliant patients was performed after the study was completed. The authors concluded that this highly compliant group of Oscal(r) patients had a 29% reduction in hip fractures compared to placebo.  These results should be taken with some caution because they represent only highly compliant subjects, and not average subject results in the trial.  The average subjects saw no difference in hip fractures rates taking a placebo or a combination of vitamin D and Oscal.