New research suggests that some women who take calcium supplements may have an increased risk of a heart attack.
Scientists from the University of Auckland said that healthy women who take calcium to protect their bones could actually do themselves more harm than good.
Previous studies have shown that calcium may protect against vascular disease by improving levels of "good" cholesterol in the blood, but the new report, which is published online in the British Medical Journal (BMJ), shows that the supplements could actually increase the chances of suffering an attack.
The latest study involved 1,471 healthy postmenopausal women aged 55 and over, with an average age of 74 years.
All the participants were split into two groups, with one group given 1g daily of calcium supplements and the other a placebo.
The study found that heart attacks were more commonly reported in the calcium group and the occurrence of any three vascular events (heart attack, stroke or sudden death) was also more common.
However, Judy O'Sullivan, cardiac nurse at the British Heart Foundation (BHF), said the findings should be treated with caution.
She said: "More rigorous research is needed before any firm conclusions are drawn as previous studies have shown calcium supplements reduce the risk of heart attacks by improving the levels of protective cholesterol."