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Os Cal Calcium Supplement

Oscal calcium supplement, according to its website, may reduce a woman’s risk of hip fracture by 29%.  Oscal is registered trademark of GlaxoSmithKline. The basis of that claim is a large clinical study called the Women’s Health Initiative. Oscal was taken twice daily by approximately 18,000 postmenopausal women between the ages of 50 and 79.  Another 18,000 received a placebo. A daily serving of the Oscal calcium supplement provided a 1000 mg of elemental calcium as calcium carbonate with 400 IU of vitamin D3.  Fractures among study subjects were monitored an average of seven years.

In the February 2006 New England Journal of Medicine article entitled Calcium plus Vitamin D Supplementation and the Risk of Fractures, Jackson et al found the following:

“Hip and Other Fractures
During a mean of 7.0 years of follow-up, there were 2102 fractures (including 175 hip fractures) among women assigned to calcium with vitamin D and 2158 fractures (including 199 hip fractures) among women assigned to placebo. (Annualized fracture rates per 10,000 person-years in the calcium with vitamin D and placebo groups, respectively, were as follows: hip fracture, 14 and 16; fracture of the lower arm or wrist, 44 and 44; clinical vertebral fracture, 14 and 15; and total fractures, 164 and 170.

Women assigned to calcium with vitamin D supplements had a nonsignificant, 12 percent lower risk of hip fracture than women assigned to placebo (hazard ratio, 0.88; 95 percent confidence interval, 0.72 to 1.08). There were no significant reductions in clinical vertebral fracture, fracture of the lower arm or wrist, or total fractures.”

Oscal Effective Only with A Subgroup
A non-significant 12% lower risk of hip fracture means that a lower percentage of women taking the Oscal calcium supplement had hip fractures compared to those taking a placebo.  However, statistically, there was no fracture rate difference between the two groups.  Scientifically, one can not claim that Oscal intake reduced fractures on average.

The authors then conducted some subgroup analysis, in which only highly compliant Oscal calcium supplement users over the seven years were analyzed.  The authors noted:

“Among women who were adherent (i.e., those who took at least 80 percent of their study medication), calcium with vitamin D supplementation resulted in a 29 percent reduction in hip fracture (hazard ratio, 0.71; 95 percent confidence interval, 0.52 to 0.97); there were 167 cases of hip fracture among these women. The hazard ratio based on the inverse-probability weighting method was nearly identical. For all other fracture outcomes, the hazard ratios were similar to those obtained in the intention-to-treat analyses."

The subgroup result is the basis of the Oscal calcium supplement claim of reducing hip fractures by 29%.  How do these results compare to other calcium studies?  Most calcium or calcium and vitamin D studies look at average fracture risk, not just results among  highy compliant patients.  For example, a very small study showed statistical reduction in AVERAGE fracture risk versus placebo among women taking AdvaCAL.  More research is needed to confirm those results.  Oscal's 29% reduction in hip fractures for some women certainly may be worth touting.  Keep in mind, however, that the average women saw no improvement in hip – or any other bone -- fracture risk while taking  the Oscal calcium supplement