The role of calcium supplementation for the prevention of osteoporosis needs to be reassessed in light of a meta-analysis showing it raises the risk of myocardial infarction, researchers say.

A pooled analysis of 11 trials involving 12 000 patients found calcium supplements exceeding 500 mg daily raised the risk of incident myocardial infarction (MI) by about 30%.

The risk of MI was higher for participants whose dietary calcium intake exceeded the median 805 mg/day, but age, sex, supplement type and vitamin D status did not affect risk.

Studies in which calcium was co-administered with vitamin D were excluded from the analysis.

The finding raises concerns about the value of recommending additional calcium without vitamin D, given the limited increase in bone density and reduction in fracture risk derived from supplementation.

“Incorporating the results from the current analysis of studies contributing patient level data, treatment of 1000 people with calcium for five years would cause an additional 14 myocardial infarctions, 10 strokes, and 13 deaths and prevent 26 fractures,” the authors wrote in the BMJ.

They said the data showed the risk of MI emerged quickly, which might indicate that the mechanism could be related to increased coagulability or altered vascular flow, or be mediated via calcium sensing hormones or indirectly via altered calcitrophic hormones.

“Because calcium supplements increase bone density it is possible that they may also increase vascular calcification and thereby cardiovascular events,” the authors added.

Given the widespread use of calcium supplements, even the small increase in risk translates into a large disease burden, and for this reason calcium supplementation for the treatment of osteoporosis should be re-evaluated, they said.

BMJ 2010; 341: c3691. doi:10.1136/bmj.c3691.
Posted 2 August, 2010

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