In a new analysis from the National Institutes of Health in the United States, men who took calcium tablets were more likely to die of heart disease over more than a decade than those who didn't get extra calcium in supplement form.

"The effect of supplemental or dietary calcium on heart disease has always been a bit of an unanswered story," says Howard Sesso, a preventive medicine researcher at Brigham and Women's Hospital and Harvard Medical School in Boston.

"It could be that when you take supplements, maybe you're taking doses that far exceed what you need," he adds. But it's still unclear how that might raise cardiovascular risks.