Risk of MI May Go Up With Calcium Supplements
Published: July 29, 2010
Effect of calcium supplements on risk of myocardial infarction and …
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Calcium supplementation appears to increase the risk of myocardial infarction, a meta-analysis showed.
Among studies of patients with or at risk for osteoporosis, those who took calcium supplements were about 30% more likely to have an MI than those who did not, Ian Reid, MD, of the University of Auckland in New Zealand, and colleagues reported online in BMJ.
Among randomized controlled trials with patient-level data, the hazard ratio for MI with supplementation was 1.31 (95% CI 1.02 to 1.67). Among those with trial-level data, the relative risk was 1.27 (95% CI 1.01 to 1.59).
“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,” the researchers wrote. “A reassessment of the role of calcium supplements in the management of osteoporosis is warranted.”
* Explain to interested patients that none of the studies included in the meta-analysis was designed to evaluate the cardiovascular risk associated with calcium supplementation.
Commenting on the study, Suzanne Steinbaum, DO, a cardiologist at Lenox Hill Hospital in New York City, said in a prepared statement that “this study helps to remind us that ‘one size does not fit all,’ even in recommending supplements and preventive care.”
“For patients who are at risk for heart disease, with multiple risk factors, or a strong family history, perhaps calcium supplementation should not be considered,” she said.
Murray Favus, MD, an endocrinologist at the University of Chicago, said in an e-mail to MedPage Today and ABC News, “I am sufficiently concerned to advise those with high calcium supplement intake to limit calcium supplement use in favor of dietary sources until the risk of supplements can be sorted out.”
Reid and his colleagues analyzed data from 11 randomized controlled trials that evaluated the use of calcium supplementation (at least 500 mg/day). They excluded studies that also administered vitamin D, which has been shown to have a cardiac benefit, in order to get a clearer picture of calcium’s effect on the heart.
None of the individual studies was designed to assess the risk of cardiovascular events.
All 11 studies — with a total of 11,921 participants and a mean duration of four years — had trial level data; five — with 8,151 total participants and a median follow-up of 3.6 years — had patient-level data.
Separate pooled analyses of patient-level and trial-level data yielded similar results, with about a 30% increased risk of MI with calcium supplementation.
None of the individual trials found a significantly increased risk, although six had nonsignificant trends in that direction.
In the analysis of patient-level data, calcium supplementation was associated with an increased risk of MI in participants who had a dietary calcium intake above the median of 805 mg/day, but not in those with lower dietary intake (P=0.01 for the interaction).
Previous studies evaluating dietary calcium intake showed a reduced cardiovascular risk with greater consumption. The difference between those results and the findings of the current study suggests “that cardiovascular risks from high calcium intake might be restricted to use of calcium supplements,” according to the researchers.
It is possible that calcium supplements elevate cardiovascular risk by increasing serum calcium levels, which have been associated with higher MI rates in observational studies, they noted.
Other possible mechanisms include an increase in vascular calcification or coagulability or altered vascular flow.
“Calcium supplements, given alone, improve bone mineral density, but they are ineffective in reducing the risk of fractures and might even increase risk, they might increase the risk of cardiovascular events, and they do not reduce mortality,” John Cleland, MD, of the University of Hull in England, and colleagues wrote in an editorial published with the study.
“[Supplements] seem to be unnecessary in adults with an adequate diet,” they added. “Given the uncertain benefits of calcium supplements, any level of risk is unwarranted.”
Considering the available evidence, the editorialists wrote, “patients with osteoporosis should generally not be treated with calcium supplements, either alone or combined with vitamin D, unless they are also receiving an effective treatment for osteoporosis for a recognized indication.”
The study authors noted that the analysis was limited in that it excluded trials in which calcium supplements were coadministered with vitamin D.
In addition, they noted, only two of the trials had data adjudicated by blinded trial investigators and seven — which accounted for 15% of the participants — had incomplete or missing data.
Noting the inherent limitations of a meta-analysis, Stephen Richardson, MD, an endocrinologist at NYU Langone Medical Center in New York City, said in an e-mail that a prospective study is needed to definitively assess the cardiovascular risk with calcium supplementation.
The meta-analysis “may temper our enthusiasm for calcium supplementation in low-risk populations,” he said, “but patients with high risk for fractures will continue to take calcium supplements.”
The analysis was funded by the Health Research Council of New Zealand and the University of Auckland School of Medicine Foundation. One of the study authors is funded by a career scientist award of the chief scientist office of the Scottish government health directorates. The Health Services Research Unit is funded by the chief scientist office of the Scottish government health directorates.
Reid has received research support from and acted as a consultant for Fonterra. He and three of his co-authors had study drugs for clinical trials of calcium supplementation supplied by Wyeth, Mission Pharmacal, Shire Pharmaceuticals, and Nycomed.
The editorialists reported that they had no conflicts of interest.
This article was developed in collaboration with ABC News.
Primary source: BMJ
Bolland M, et al “Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis” BMJ 2010; DOI: 10.1136/bmj.c3691.
Additional source: BMJ
Cleland J, et al “Calcium supplements in people with osteoporosis” BMJ 2010; DOI: 10.1136/bmj.c3691.