Calcium supplementation -- without giving vitamin D at the same time -- appears to increase the risk of myocardial infarction, a new review of past research has shown.
Among studies of patients with or at risk of osteoporosis, those who received calcium supplements were about 30 percent more likely to have a heart attack than those who did not, Dr. Ian Reid, MD of the University of Auckland in New Zealand and colleagues reported online in BMJ.
"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."
In a statement, Dr. Suzanne Steinbaum, a cardiologist at Lenox Hill Hospital in New York City, said, "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.
Dr. Murray Favus, an endocrinologist at the University of Chicago, said, "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 11 different trials that evaluated the use of calcium supplementation (at least 500 mg/day). None of the individual studies was designed to assess the risk of cardiovascular events.
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 blood serum calcium levels, which have been associated with higher heart attack rates in observational studies, the researchers noted in their paper.
"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," Dr. John Cleland of the University of Hull in England and colleagues wrote in an accompanying editorial.
"They 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, they 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 given along with vitamin D.
Noting the limitations of the review, Dr. Stephen Richardson, an endocrinologist at NYU Langone Medical Center, said that more research 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."