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.
"The effect of supplemental or dietary calcium on heart disease has always been a bit of an unanswered story," said Dr Howard Sesso, a preventive medicine researcher at Brigham and Women's Hospital 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 in eight states, initiated in 1995 to 1996. About half of men and more than two-thirds of women said they took calcium supplements or multivitamins containing calcium at the outset.
12 000 people died of cardiovascular disease
Over the next 12 years, almost 12 000 people - or about 3% - died of cardiovascular disease.
According to Dr Qian Xiao from the National Cancer Institute and her colleagues, men who took at least 1 000 mg of calcium per day in supplement form were 20% more likely to die of heart disease (but not cerebrovascular disease) than those who didn't, after adjustment for age, race, weight, and other measures of diet and lifestyle.
There was no link between calcium supplements and heart disease deaths in women, however. And calcium from food and beverages wasn't tied to heart problems in either gender, the research team wrote in JAMA Internal Medicine.
It's possible that calcium deposits in arteries and veins may affect cardiovascular risks in some people, Dr Xiao wrote in an email to Reuters Health.
Heart problems reported in men
But Dr Sesso, who wasn't involved in the new study, told Reuters Health he wasn't sure why calcium supplements would be linked to a higher risk of heart problems in men but not women.
It's possible there were certain differences between men who did or didn't take extra calcium that the research team couldn't measure.
"Although we observed an increased risk of death from heart disease in men who reported taking supplements containing calcium, we cannot say for sure that it was a result of using those supplements," Xiao said.
According to Dr Sesso, the study won't change the fact that calcium supplements are typically recommended for reasons not related to heart disease - such as to prevent fracture risk in older adults who don't consume enough calcium through food.
(Genevra Pittman, Reuters Health, February 2013)
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