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Calcium supplements may increase the risk of heart damage and plaque buildup in arteries, even though a diet high in calcium-rich food appears to help protect the heart, a study concludes.

The analysis is based on 10 years of study of more than 2,700 people.

The researchers caution that their work, published in the Journal of the American Heart Association, documents an association between calcium supplements and atherosclerosis. It does not prove cause and effect.

But they say the results add to growing scientific concern about calcium supplements, often taken by aging persons to prevent bones from becoming brittle; they urge patients to consult with a knowledgeable physician before using them.

“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,” says Erin Michos, associate director of preventive cardiology and associate professor of medicine at Johns Hopkins University. “But our study adds to the body of evidence that excess calcium in the form of supplements may harm the heart and vascular system.”

An estimated 43 percent of US adults take a supplement that includes calcium. Earlier studies showed that calcium taken that way, particularly in older people, doesn’t all “make it to the skeleton or get completely excreted in the urine, so … must be accumulating in the body’s soft tissues,” says nutritionist and study coauthor John Anderson of the University of North Carolina Gillings School of Global Public Health. Scientists also knew that as a person ages, calcium-based plaque builds up in the aorta and other arteries, impeding blood flow and increasing the risk of heart attack.

“There is clearly something different in how the body uses and responds to supplements versus intake through diet that makes it riskier.”

The investigators looked at data from the Multi-Ethnic Study of Atherosclerosis, a long-running research project at six research universities, including Johns Hopkins. They focused on 2,742 participants who had CT scans 10 years apart.

The ethnically diverse participants ranged in age from 45 to 84; 51 percent were female. In 2000, all completed a 120-part questionnaire about their dietary habits to determine how much calcium they took in by eating dairy products; leafy greens; calcium-enriched foods, like cereals; and other calcium-rich foods. Separately, the researchers inventoried what drugs and supplements each took. The investigators used cardiac CT scans to measure participants’ coronary artery calcium scores, a marker of heart disease risk.

After adjusting for heart disease risks like age, sex, race, exercise, smoking, income, education, weight, drinking, blood pressure, blood sugar, and family history, the researchers separated out the 20 percent of participants with the highest total calcium intake, greater than 1,400 milligrams a day. That group was on average 27 percent less likely than the 20 percent with the lowest calcium intake—less than 400 milligrams—to develop heart disease, as indicated by their coronary artery calcium test.

Next, the investigators focused on the differences between those taking in only dietary calcium and the 46 percent using calcium supplements, like pills, chewables, liquids, and powders.

The researchers again adjusted for other risks and found that supplement users showed a 22-percent increased likelihood after a decade of coronary artery calcium scores indicating development of heart disease.

“There is clearly something different in how the body uses and responds to supplements versus intake through diet that makes it riskier,” Anderson says. “It could be that supplements contain calcium salts, or it could be from taking a large dose all at once that the body is unable to process.”

Participants with highest calcium intake from food—more than 1,022 milligrams a day—showed no increase in relative risk of developing heart disease.

“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 says. “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 them.”

The US Centers for Disease Control and Prevention say coronary heart disease kills more than 370,000 people each year in the United States. More than half of women over 60 take calcium supplements—many without physician oversight—to reduce osteoporosis risk.

Coauthors of the study are from the University of Washington; Indiana, Wake Forest and Emory universities; the Patient-Centered Outcomes Research Institute; and UCLA Medical Center. The National Institutes of Health and the Blumenthal Scholars Award in Preventive Cardiology funded the study.

Source: Johns Hopkins University