This analysis looked at 1,471 postmenopausal women with a mean age of 74 who had previously participated in a study looking at the effects of calcium on bone density and fracture rates. The findings were expected to be published online Jan. 16 in the BMJ.
All women had been randomly assigned to receive either calcium or a placebo.
Women in the calcium group had slightly more than twice the risk of having a heart attack compared with women taking the placebo.
Women taking calcium had a 47 percent higher risk of having any one of three "events" (heart attack, stroke or sudden death) than women in the placebo group.
The authors then took the unusual step of checking hospital admissions and reviewing death certificates to find any previously unreported events.
When these were added to the mix, the relative risk of having a heart attack or one of the composite events decreased somewhat, though women taking calcium were still at a higher risk. Now women taking calcium had a 49 percent greater risk of having a heart attack and a 21 percent higher risk of having one of the three composite events.
The findings seem odd in light of calcium's beneficial effect on cholesterol. Yet the supplement has also been found to elevate blood calcium levels, which could speed up calcification of the blood vessels. Previous research has found that calcium build-up in the arteries can foreshadow coronary artery disease.
"There is a point here that is even more subtle, which is that lipids are not the only factors that are giving you cardiac risk," Roos said.
The picture is even further complicated by the fact that calcium is often taking in conjunction with a class of drugs known as bisphosphonates. Earlier this month, the U.S. Food and Drug Administration issued an alert regarding the possibility of severe and sometimes even incapacitating bone, joint and/o
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