Calcium supplements may increase cardiovascular risk
MedWire News: Calcium supplements may increase people's cardiovascular risk, report researchers who call for their use in treatment and prevention of osteoporosis to be reviewed.
In meta-analyses of 11 placebo-controlled trials, they found a 30% increased relative risk for myocardial infarction (MI) over 4 years in people taking calcium supplements (≥500 mg/day).
The risk seemed to be greater in people with above-median dietary calcium intake but was independent of age, gender, and type of supplement, report Ian Reid (University of Auckland, New Zealand) and colleagues in the British Medical Journal.
Small, nonsignificant increases in the risk for stroke and total mortality were also observed with calcium supplementation.
"As calcium supplements are widely used these modest increases in risk of cardiovascular disease might translate into a large burden of disease in the population," write Reid and team.
The researchers did both patient-level and trial-level analyses. In five trials with patient-level data, including 8151 participants, 143 people allocated to calcium had a MI over the median 3.6-year follow-up compared with 111 allocated to placebo, equating to a hazard ratio for incident MI of 1.31 (p=0.035).
Analysis of trial-level data gave a similar result: among 8151 participants, 166 people who took calcium compared with 130 in the placebo group had a MI over follow-up lasting a mean of 4.0 years, giving a pooled relative risk of 1.27 (p=0.038).
Subgroup analyses suggested that the increased risk for MI with calcium treatment was evident in those with dietary calcium intake above the median of 805 mg/day (HR=1.85) but not in those with lower dietary calcium intake (HR=0.98).
The researchers emphasize that the trials included people taking calcium supplements alone, and "the results therefore may not apply to coadministered calcium and vitamin D supplements."
They conclude: "Given the modest benefits of calcium supplements on bone density and fracture prevention, a reassessment of the role of calcium supplements in the management of osteoporosis is warranted."
John Cleland (University of Hull, UK) and colleagues comment in a related editorial that although vitamin D seems to mitigate against the increased risk in cardiovascular events with calcium, there are no conclusive data to show that calcium and vitamin D supplements, either alone or in combination, reduce fracture risk.
However, among other treatments shown to be effective for osteoporosis, bisphosphonates and raloxifene have generally been given in addition to calcium and vitamin D, they note.
Speaking to MedWire News, Cleland commented that it was surprising to see only a trend towards increased mortality despite the increase in MIs, leading him to question whether "the calcium, rather than causing more heart attacks, was actually just causing more heart attacks to be diagnosed."
So, if taking the calcium caused indigestion, he explained, this could lead to a person having a precautionary electrocardiogram, which picks up a previous MI that otherwise would not have been diagnosed.
Until more research is completed, he said, "you have to back off and take a look at the bigger picture, and the fact is that calcium supplements don't seem to do much good, and there is a worry that they might cause some harm."
There are certain patient groups, for example people with malabsorption syndromes, or kidney disease, that may need to continue calcium supplementation, he noted.
"But for the average person in their 50s [or older] worried about developing osteoporosis, I don't think there is any evidence that calcium meaningfully alters their likelihood of developing a fracture and there is this concern that it may increase the risk of vascular events, so on balance they should probably stop taking them."
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By Caroline Price