Calcium supplements may raise heart attack risk

By Liam Davenport

Increased dietary calcium intake has no overall cardiovascular benefits, and calcium supplements appear to raise the risk for myocardial infarction (MI), warn investigators.

Previous epidemiological studies have demonstrated an inverse association between dietary calcium intake and the risk for hypertension, obesity, and Type 2 diabetes, leading to suggestions that the risk of cardiovascular events may be reduced by a higher intake.

To test this hypothesis, Sabine Rohrmann, from the University of Zurich in Switzerland, and colleagues examined data on 23,980 participants from the Heidelberg cohort of the European Prospective into Cancer and Nutrition study.

The participants, who were aged 35-64 years and free from cardiovascular disease at recruitment, completed the Food Frequency Questionnaire and were assessed for cardiovascular events over an average follow-up of 11 years.

There were 354 MIs, 260 strokes, and 267 cardiovascular disease deaths during follow-up, the team reports in Heart.

In multivariate analysis, a higher dietary calcium intake was associated with a reduced risk for MI, at a hazard ratio (HR) of 0.69 for people in the third quartile of intake as compared with the lowest quartile.

However, people who took calcium supplements had a significantly increased risk for MI compared with nonusers, at a HR of 1.86. The HR increased to 2.39 when the analysis was restricted to individuals who used only calcium supplements, and to 2.70 after excluding MIs that occurred in the first 2 years of follow up.

The team concludes: "This study suggests that increasing dietary calcium intake from diet might not confer significant cardiovascular benefits, while calcium supplements, which might raise myocardial infarction risk, should be taken with caution."

In an accompanying editorial, Ian Reid and Mark Bolland, from the University of Auckland in New Zealand, comment: "Calcium supplements have been widely embraced... on the grounds that they are a natural and therefore safe way of preventing osteoporotic fractures.

"It is now becoming clear that taking this micronutrient in one or two daily [doses] is not natural."

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