The British Medical Journal has published the results of a meta-analysis that has identified an increased risk of heart attacks in people taking calcium supplements. This analysis has been reported in the general media (BBC).
The analysis identified 15 trials, 5 with patient level data involving 8,151 participants with a median follow up period of 3.6 years and 11 with trial level data involving 11,921 participants with a mean duration of 4.0 years.
The analysis of patient level data found an increased risk of myocardial infarction (Hazard ratio 1.31, 95% CI 1.02 - 1.67, p=0.035) with a similar risk identified in the trial level data (Relative risk 1.27, 95% CI 1.01 - 1.59, p=0.038). There were also non-significant increases in strokes and deaths.
The authors conclude, "Calcium supplements (without co-administered vitamin D) are associated with an increased risk of myocardial infarction" and they urge a review of practice in the management of osteoporosis.
It should be noted that this analysis reviewed calcium supplement against placebo. Vitamin D is known to reduce mortality and as such trials including vitamin D were only included in the analysis if both study groups were treated with vitamin D; this applied to just one study in the 15 analysed.
Using the figures reported in the 11 trial analysis, there were 166 myocardial infarctions among 6,116 participants taking the calcium supplement (absolute risk of 2.71%) versus 130 myocardial infarctions in 5805 participants in the placebo group (absolute risk of 2.24%). This means that if 213 patients are treated with calcium instead of placebo for a period of 4 years 1 patient will be caused to have a heart attack (NNH = 213).
Action: Clinicians should be aware of this study and the media coverage. It would seem prudent to change patients from supplements that only contain calcium to those that also contain vitamin D or to discuss dietary changes to ensure adequate intake of calcium.