The calcium supplements that many older women take to boost their bone health may increase their risk for heart disease, a study shows.
"Calcium supplements, with or without vitamin D, mostly increase the risk of cardiovascular events, especially [heart attack]," concludes study researcher Dr. Ian Reid, 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 mg 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.
Calcium and Heart Attack Risk
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 Dr. Suzanne Steinbaum, 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.
"Preventive health isn't really a one-size-fits-all proposition," she says. "If you are a woman who has a greater risk for heart disease vs. a greater risk of osteoporosis and fractures, perhaps calcium supplementation is not something for you to take," she says.
Major heart disease risk factors include high blood pressure, high cholesterol, diabetes, smoking, obesity, sedentary lifestyle, and family history.
"Think twice about calcium if you are at risk for heart disease, but this study is not the final answer," she says.
Not so fast, says WHI study author Dr. JoAnn Manson, the chair of preventive medicine department at Brigham and Women's Hospital in Boston.
"This is a selective re-analysis of certain subgroups of the WHI calcium and vitamin D trial," she says.
"Overall, there was no evidence of an increase or decrease in risk for coronary heart disease or stroke with use of calcium and vitamin D," she says.
What's more, another arm of the WHI, which looked at coronary artery calcium levels, showed no evidence of increased heart risks among women who were randomly assigned to calcium plus vitamin D.
Dr. Nieca Goldberg, medical director of the Women's Heart Program at NYU Langone Medical Center in New York, says women must be aware of how much calcium they get through diet and how much they get through supplements to avoid getting too much of this mineral.
"Calculate how much you are eating through food and balance off the rest with supplements so it equals 1,200 milligrams of calcium a day for women older than 50," she says.
"Women should also take a global approach to their heart disease risk and get risk factors evaluated," she says. "Calcium intake alone is not the only risk marker for heart disease."