Are Calcium Supplements Safe?

New research is prompting questions about the safety of the calcium supplements that so many women age 50 and older take to strengthen their bones. One recent study suggests these pills raise a person's risk for a heart attack, and another new study—scheduled to be presented next month—is expected to raise more safety questions, continuing the debate that erupted this summer.

The controversy began in July when the British Medical Journal published a study that raised troubling questions about the calcium supplements taken by millions of Americans to ward off the bone thinning that comes as we age.

Ian R. Reid, M.D., of New Zealand, led a team that examined data from 15 clinical trials involving calcium supplements, and reported a roughly 30 percent increase in heart attacks among those taking the pills. The team also found, however, that the supplements had no significant effect on strokes or on the risk of death from a heart attack.

"We think that the evidence is fairly compelling that calcium supplementation is causing heart attacks," says Reid, a professor of medicine and endocrinology at the University of Auckland. In his own practice, he says, "we almost never prescribe calcium supplements these days." He advises people "to change their diet so they get what they need from eating conventional foods."

Calcium in food no risk

This latest research may call into question the popular practice of getting calcium from pills, but it has not suggested any heart risk from calcium in the diet. Researchers say that may be because food doesn't cause the same temporary, short-term boost in blood calcium as supplements. The authors say this boost produces calcium deposits that may harden the blood vessels or make the blood more likely to clot.

But U.S. doctors widely recommend calcium supplements, especially to postmenopausal women at risk for osteoporosis—thinning and fractured bones—and some say the evidence linking the pills to heart risk is not yet persuasive enough to change that policy.

"I don't think it's enough to tell our patients to stop using calcium," says Lynne Braun, a researcher and nurse practitioner who counsels patients on cardiovascular risk at the Heart Center for Women at Rush University Medical Center in Chicago. "I personally use calcium supplementation. Would I stop based on this [study]? The answer is no."

Braun says the new study suffers from the usual shortcomings of meta-analysis, a statistical method that pools data from a variety of studies that haven't necessarily gathered information on the same questions or in the same ways.

Robert R. Recker, M.D., director of the Osteoporosis Research Center at Creighton University in Omaha, Neb., points out that when the New Zealand team looked at trials where specific patient information was available on more than 8,000 people, their analysis found 143 heart attacks among those who took calcium pills and 111 in the comparison group—a spread he calls "underwhelming."