Treating osteoporosis: concerns about calcium

I enjoyed reading the recent article by Akhil Gupta and Lyn March on the treatment of osteoporosis.1 I especially appreciated the inclusion of the numbers needed to treat (NNTs) with antiresorptive drugs to prevent a fracture. Such measures of absolute benefit are helpful for shared decision-making with our patients. However, I was disappointed that the same care was not taken in the discussion of calcium supplementation. Here, the authors simply stated that ‘combined calcium and vitamin D supplements seem safe and effective for most people who require them’.

I agree with the authors’ concerns that the cardiovascular safety of calcium supplementation are unresolved.2,3 In this context of possible harm, I believe we need to carefully consider the purported benefits of calcium. A systematic review found that calcium supplementation has little if any effect in reducing fracture.4 There was an overall 11% (95% CI* 4–19%) relative risk reduction in total fracture, which became smaller and statistically insignificant when the authors restricted their analysis to trials at low risk of bias (4%, 95% CI 1–9%). For the typical person with osteoporosis, these figures will equate to large NNTs for fracture prevention – much larger than those for antiresorptive drugs – if indeed there is any real benefit at all. I struggle to see then how calcium supplementation can be deemed ‘effective for most people’ as claimed.