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Study: Calcium May Increase Heart Attack Risk

But Experts Say Evidence Is Not Convincing
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WebMD Health News
Reviewed by Laura J. Martin, MD

July 29, 2010 -- Millions of people who take calcium supplements in hopes of lowering their risk for bone fractures may actually be increasing their risk of having a heart attack, new research suggests.

An analysis of close to a dozen clinical trials involving about 12,000 patients found calcium supplementation to be associated with a 20% to 30% increase in heart attack risk.

Researcher Ian Reid, MD, of New Zealand’s University of Aukland says it is time to reassess the role of calcium supplementation for the treatment and prevention of osteoporosis.

“I think we need to seriously consider whether calcium supplementation is a good thing for most people, given that it is associated with a very small decrease in fracture risk,” he tells WebMD.

Calcium, Heart Attack Findings

Just over two years ago, Reid’s own research unexpectedly showed a slight increase in heart attacks among healthy, older women who took calcium supplements to prevent fractures.

“Our hypothesis when we started the study was that calcium would protect the heart,” he says.

In an effort to confirm the earlier findings, Reid and colleagues from the University of Aberdeen in the U.K. and Dartmouth University in the U.S. combined and analyzed the findings from 11 randomized trials in which participants took calcium supplements (500 milligrams or more per day) without vitamin D.

After adjusting for differences in study design, the researchers concluded that calcium supplementation was associated with a modest increase in risk for heart attacks, but not for strokes or death from heart disease.

Reid speculates that calcium supplements may rapidly elevate blood calcium levels, which could contribute to artery disease.

Calcium from food sources is absorbed much more slowly, he says.

The study appears today in the journal BMJ Online First.

“We encourage our patients to get their calcium from the foods they eat and not from supplements,” he says.

Calcium-Bone Link ‘Weak’

In an interview with WebMD, cardiologist John Cleland of the U.K.’s Hull York Medical School called the analysis “concerning but not convincing” in linking calcium supplementation to heart attacks.

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