A new study casts a shadow on calcium, the essential mineral known to help keep bones strong, hearts healthy and blood pressure controlled.
New Zealand researchers report in the journal BMJ that otherwise-healthy, postmenopausal women who took calcium supplements were about twice as likely to suffer a heart attack as those who skipped the supplements.
That finding is surprising, because previous research has shown that calcium helps improve the ratio of healthy to unhealthy cholesterol by as much as 20 percent. Such changes are linked with a 20 percent to 30 percent reduction in so-called vascular events, including heart attacks. Other research with both calcium and vitamin D shows improvements in overall mortality among those who take the supplements.
So what accounts for the increased heart attacks?
"I don't know what to make of it," says Robert P. Heaney, a professor of medicine at Creighton University in Nebraska, who has conducted numerous calcium studies. "I think we just have to say that the jury is out."
Heaney noted that there is a large body of information showing calcium's benefits: "I don't expect that to go away."
Heaney has agreed to collaborate with New Zealand researcher Ian Reid to try to figure out why women who took calcium supplements in the study had an increased risk of heart attacks. "We will see," he said, "if the findings pan out."