A study is raising new questions about the safety of calcium, which many women take to protect their bones.
An analysis of data collected from more than 16,000 women who participated in the landmark Women's Health Initiative found that those who started taking calcium as part of the study were at increased risk for heart attacks and strokes.
When the data from that study were originally analysed it found no increased risk for heart problems among women taking calcium and Vitamin D. But most of the women in the study were already taking calcium on their own, which may have hidden any risks.
So Ian Reid of the University of Auckland and his colleagues reanalysed the data to try to take that into account. The new analysis of data from 16,718 women, published in the British medical journal known as BMJ, found that the women who were not taking calcium when the study started but began taking it when they got into the research project were at 13 to 22% increased risk. The risk occurred regardless of whether the women were taking calcium alone or combined with Vitamin D, the researchers found.
The researchers also analysed data from 13 other studies involving 29,000 people all together, and found increases in the risk for heart attacks and strokes among those taking calcium.
The researchers speculate that there may be something about suddenly starting calcium that boosts the risk, perhaps by causing calcification, or hardening, of the arteries. Calcium may also make it more likely that blood clots will form, they said.
(In exclusive partnership with The Washington Post)