“Calcium supplements, with or without vitamin D, mostly increase the risk of cardiovascular events, especially [heart attack],” concludes study researcher Ian Reid, MD, a professor of medicine and endocrinology at the University of Auckland in New Zealand. “A reassessment of the role of calcium supplements in osteoporosis management is warranted.”
The study is published in the journal BMJ.
Researchers re-analyzed data from the Women’s Health Initiative (WHI) that looked at calcium and vitamin D supplements. The initial study of 36,000 women showed no increased risk for heart disease among those who received 1,000 milligrams of calcium and 400 international units (IU) of vitamin D per day, compared with those who were randomly assigned to receive a placebo.
But some of these women were also taking personal calcium supplements, which could have masked the initial findings.
Reid and colleagues looked at a subgroup of 16,718 women who were not taking calcium supplements on their own when the WHI began. In this analysis, women who were taking calcium and vitamin D as part of the trial were at greater risk for heart disease, namely heart attacks.
Analysis of data from 13 other trials backs up these findings, showing that taking calcium supplements with or without vitamin D may increase risk of heart attack and stroke.
The researchers suspect that the sudden change in blood calcium levels when starting a supplement is responsible for the increased risk, meaning that women who already had calcium in their blood due to personal supplement use may have been immune to this abrupt spike.
“High levels of calcium in the blood can lead to clotting abnormalities and greater risk for heart attack,” says Suzanne Steinbaum, MD, director of women and heart disease at Lenox Hill Hospital in New York.
As for whether a woman should scrap her calcium supplements to protect her heart, Steinbaum says there are no simple answers.