OS-CAL (Calcium Carbonate) or Calcium Citrate?
Are there differences in clinical effectiveness?
The two most common calcium salts found in calcium supplements today are calcium carbonate (OS-CAL) and calcium citrate (Citracal®). Both are available in formulations that include calcium and vitamin D but these products differ in important ways that can directly affect patients.
Only OS-CAL has demonstrated a 29%*1 hip fracture risk reduction, calcium citrate (Citracal®) has not
The National Institutes of Health's (NIH) Women's Health Initiative (WHI) Calcium Plus Vitamin D Trial tested whether 36,282 healthy postmenopausal women treated with calcium carbonate and vitamin D3 supplements would have a lower risk of hip fracture than women receiving placebo.1
A sub-analysis identified a significant 29% reduction in hip fracture risk in patients who were adherent to the study medication (500 mg calcium carbonate plus 200 IU vitamin D3 BID - the OS-CAL formulation), with adherence defined as taking > 80% of study medications.1
29% risk reduction should not be considered as a class effect
Calcium plus vitamin D formulations, other than the formulations used in the WHI study (OS-CAL), would not necessarily produce comparable clinical outcomes because products differ in important ways that directly affect patients. There are too many confounding differences between products.2
The bioavailability of 8-12 different calcium carbonate sources was evaluated based on 900 individual absorption measurements under identical test conditions:2
- Mean absorbability varied from source to source by more than a factor of 2X
Dr. Robert P. Heaney† speculates that these variations are likely caused by pharmaceutical issues such as excipients, flavourings, and tableting specifications.2 He confirmed that there are too many possible variations related to tablet composition and manufacturing procedures to permit generalizing absorbability data from one product to another, even when the active component is chemically identical.2