People who take calcium supplements may be at increased risk for developing buildups of plaque in their arteries, which is a sign of heart disease, a new study found.
However, people who consume a lot of calcium through the food they eat may actually be at a lower risk of heart disease, the study showed.
The findings add to a growing body of evidence that some dietary supplements, such as calcium supplements, may have harmful effects.
"When it comes to using vitamin and mineral supplements, particularly calcium supplements being taken for bone health, many Americans think that more is always better," study co-author Dr. Erin Michos, associate director of preventive cardiology at the Johns Hopkins University School of Medicine in Baltimore, said in a statement. "But our study adds to the body of evidence that excess calcium in the form of supplements may harm the heart and vascular system." [7 Foods You Can Overdose On]
In the study, the researchers analyzed information from more than 2,700 people ages 45 to 84, who answered questions about their calcium intake, from both their diets and supplements.
The participants also underwent two CT scans, one at the beginning of the study and another 10 years later. The scans looked for plaques containing calcium in the arteries of the heart, which are the coronary arteries. The presence of such calcium-containing plaques means that a person is at increased risk of developing heart disease, or having a heart attack. At the start of the study, about 1,500 people did not have any calcium-containing plaques in their arteries.
The researchers then divided people into five groups based on the individuals' calcium intake from both their diets and supplements.
The people with the highest intake of calcium (greater than 1,400 milligrams per day) were actually 27 percent less likely to develop calcium-containing plaques in their coronary arteries over the 10-year study, compared with the group with the lowest intake of calcium (less than 400 mg per day). Moreover, the people in the highest-intake group who achieved their high calcium intake without supplements were at an especially low risk of developing plaques, according to the study.
In contrast, people who took calcium supplements were overall 22 percent more likely to develop calcium-containing plaques over the study period, compared with those people who didn't use such supplements. Forty-six percent of people in the study used calcium supplements.
It's possible that large doses of calcium consumed in supplements may temporarily elevate calcium levels in the blood, which leads to calcifications in blood vessels, the researchers said.
"There is clearly something different in how the body uses and responds to supplements versus intake through diet that makes it riskier," said study co-author John Anderson, a professor emeritus of nutrition at the University of North Carolina at Chapel Hill. "It could be from taking a large dose all at once that the body is unable to process."
The researchers noted that they found only an association and cannot prove that taking calcium supplements causes an increase in the risk of developing calcium-containing plaques and heart disease. In addition, the participants self-reported their calcium intake, and it's possible they did not always remember their intake correctly, which could affect the results, the researchers said.
Previous research supports the new study's results, though. A 2012 study from Sweden found that consuming high amounts of calcium was linked with an increased risk of dying from any cause during the study period, including from heart disease.
The researchers said their new results are "hypothesis generating" and should spur more research in this area.
"Based on this evidence, we can tell our patients that there doesn't seem to be any harm in eating a heart-healthy diet that includes calcium-rich foods, and it may even be beneficial for the heart," Michos said. "But patients should really discuss any plan to take calcium supplements with their doctor to sort out a proper dosage or whether they even need" such supplements.
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