Study Sparks Uncertainty About Cardiovascular Effects of Calcium Supplements in Postmenopausal Women

A study recently published in BMJ raises questions about the overall safety of calcium supplementation in healthy postmenopausal women.

The results of the study, titled "Vascular events in healthy older women receiving calcium supplementation: randomized controlled trial," suggest a link between calcium supplementation and increased rates of adverse cardiovascular events in postmenopausal women. The study's authors urge clinicians to balance this new information against the acknowledged benefits of calcium on bone health.

The New Zealand study followed 1,471 healthy postmenopausal women (mean age 74) for five years to determine the effect calcium supplementation had on myocardial infarction, stroke and sudden death. About half of the women were randomized to the calcium supplementation group, and the remainder received a placebo. In all, 396 women in the treatment group took the study drug for the entire five years, and 443 women in the control group completed the full five-year course.

This preplanned secondary analysis relied on data collected to assess the effects of calcium supplementation on bone density and fracture incidence in healthy postmenopausal women. Women in the calcium group received 1 gram of elemental calcium (Citracal, in this case) each day. Researchers followed up with the study participants every six months to record adverse events. In a move they noted as somewhat unusual for this type of study, the researchers also mined the New Zealand national database of hospital admissions to search for unreported events.

Myocardial infarction was more common among participants in the calcium group than those in the placebo group. Twenty-one women in the calcium group reported at least one myocardial infarction, compared with 10 in the placebo group, as verified by researchers. The composite end point of myocardial infarction, stroke or sudden death also was slightly more common among participants taking calcium supplements, the study found. However, when researchers included data from the country's national database of hospital admissions, those findings lost statistical significance.

The study authors acknowledged that even though the new data raise some concerns, they could not draw a definitive conclusion on the impact of calcium supplementation on cardiovascular health. In addition to the study being small in size for the end points considered, the women participating were mostly elderly and white, preventing generalization of the findings to other age and racial groups.

Although many calcium supplementation studies do not mention vascular events, the authors of this study report found three other studies that showed slight trends similar to those uncovered in the current study. The authors write, "Taken together, these four studies raise major concerns about the cardiovascular safety of calcium supplementation, particularly with respect to myocardial infarction in older postmenopausal women."