There's fresh evidence that older women who take calcium supplements to protect their bones are inadvertently endangering their cardiac health.
A new study published on Friday in the British Medical Journal found that calcium supplements were associated with a 30 per cent increased risk of having a heart attack.
"We believe doctors should be re-assessing the risks and benefits of calcium supplements in the management of osteoporosis," said the senior author of the paper, Ian Reid of the University of Auckland in New Zealand.
Dr. Reid was the part of a New Zealand research team that raised safety concerns about the popular supplements two years ago. At that time, the team published the findings from a five-year study of 1,471 postmenopausal women that revealed a higher rate of heart attacks and strokes among women taking calcium supplements compared to those given placebos.
Those findings surprised many experts, and led the New Zealanders to embark on a larger study. They joined forces with researchers in Britain and the United States to see if there was any hint of heart problems among women who participated in earlier trials of calcium supplements. Overall, they analyzed 11 randomized controlled trials involving 12,000 patients, and concluded that supplements seemed to nudge up the heart attack risk by 30 per cent.
However, an editorial accompanying the new study in the BMJ noted that more research will be needed to determine if the heart attack risk is real. The latest analysis did not look at the what happens when calcium is taken with vitamin D - a popular combination.
In the meantime, Dr. Reid said patients should discuss the issue with their health-care providers. What's more, he said, they may want to consider boosting their calcium levels through dietary sources, rather than supplements. There are also prescription medications designed to minimize bone loss in patients who are considered to be at high risk of developing osteoporosis.
He said calcium supplements are not necessarily the best way to protect bones, adding that they may reduce the chances of fractures by only 10 per cent. In his opinion, the modest benefit may not be worth the potential risk.
Although the researchers aren't sure how supplements may set the stage for a heart attack, there is some evidence that the pills can lead to a rapid rise in the calcium levels in the bloodstream. That spike may damage blood vessels or cause blood clots, he speculated. "To some extent, it's an artificial input in the body."
By contrast, the mineral is released from food sources at a slower pace, "so you just have a steady trickle of calcium into the bloodstream," Dr. Reid explained.
John Cleland of the University of Hull in Britain, and a co-author of the BMJ editorial, believes the prudent thing for most women to do is forgo supplements.
"I am not convinced the effects [of more heart attacks]are real," he said. But he added that there is also very little reason to believe that the tablets are actually helping to prevent bone fractures.
"I think the lack of evidence of benefit from these calcium supplements means that the appropriate and measured response is to stop taking them," Dr. Cleland said.