In a new analysis from the National Institutes of Health, 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," said 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 added. But it's still unclear how that might raise cardiovascular risks.
The new findings are based on a study of close to 400,000 middle-aged Americans initiated in 1995 to 1996.
Study volunteers answered questions about their lifestyle, general health and diet, including use of supplements. Researchers then tracked how many of them died, and from what causes, over the next 12 years.
About half of men and more than two-thirds of women said they took calcium supplements or multivitamins containing calcium at the outset.
During the study period, almost 12,000 people - or about three percent - died of cardiovascular disease.
Qian Xiao from the National Cancer Institute and her colleagues found men who took 1,000 milligrams of calcium per day or more were 20 percent more likely to die of heart-related causes than those who passed on calcium supplements. That was after the researchers took into account men's age, race and weight, as well as other measures of diet and lifestyle.
It's possible that calcium build-up in the arteries and veins may affect cardiovascular risks in some people, Xiao added.
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