By Robert Preidt
The study couldn't prove the supplements help cause heart trouble, but its authors believe the finding should give consumers pause for thought.
"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," said study lead author Dr. Erin Michos.
"But our study adds to the body of evidence that excess calcium in the form of supplements may harm the heart and vascular system," Michos said in a news release from Johns Hopkins University School of Medicine in Baltimore.
She is associate director of preventive cardiology at the school's Ciccarone Center for the Prevention of Heart Disease.
About 43 percent of American adults now take a supplement that includes calcium, according to the U.S. National Institutes of Health. And more than half of women over 60 take calcium supplements to reduce their risk of osteoporosis.
In the new study, Michos' team analyzed data from 10 years of medical tests on more than 2,700 adults in a U.S. government-funded heart disease study. Participants ranged in age from 45 to 85, and they were questioned on their daily diet and the supplements they took.
Participants also underwent CT scans aimed at measuring calcification of their arteries -- a known heart risk factor.
After adjusting for factors that included education, exercise, weight and income, the research showed that people in the top fifth in terms of calcium intake -- from whatever source -- had a 27 percent lower risk of heart disease, compared to those in the bottom one-fifth.
However, that statistic looked at total calcium intake in people who took in the nutrient from food and/or supplements.
Going a step further, Michos and her colleagues separated out calcium intake by source.
They found that people who took calcium supplements had a significant increase in the risk of plaque buildup in their arteries, as well as in their odds for heart disease, compared to people who didn't take the supplements.
Michos' group believes the findings add to growing concerns about the potential harms of calcium supplements as opposed to calcium from foods. The researchers believe people should talk with a well-informed doctor before using the products.
However, while calcium supplements may pose a risk to the heart, foods that are naturally high in calcium do not -- and may even help protect the heart, the researchers said.
According to the National Osteoporosis Foundation, foods rich in calcium include milk and many dairy products, broccoli, oranges and beans, among others.
"There is clearly something different in how the body uses and responds to supplements versus intake through diet that makes it riskier. 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," study co-author John Anderson said in the news release. He is a professor emeritus of nutrition at the University of North Carolina.
Michos added: "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. 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 Council for Responsible Nutrition represents supplement makers. In a statement, Duffy MacKay, senior vice president of scientific and regulatory affairs at the CRN, focused on the "total calcium" finding.
"This observational study demonstrated that people with the highest total calcium intake from both food and dietary supplements had the lowest risk of coronary artery calcification," he said. "This confirms the safety of calcium supplementation for heart health, which has been the conclusion of several large studies in recent years."
However, one heart specialist who reviewed the new findings disagreed. Dr. Suzanne Steinbaum said the study's conclusion is different when the spotlight is placed on supplements alone.
"Calcium supplements have long been questioned when it comes to the development of heart disease," said Steinbaum, who directs Women's Heart Health at Lenox Hill Hospital in New York City. "It is clear that excess calcium, which is often the result of supplementation, can be dangerous for heart health.
"Calcium supplements should not be considered safe just because they could be purchased over the counter," she added. "The true risk of heart disease must be considered and options or alternatives explored."
Dr. Howard Selinger is chair of family medicine at Quinnipiac University's Netter School of Medicine in North Haven, Conn. He reviewed the new study and noted that other data has suggested that calcium supplements might also raise a patient's odds for kidney stones.
Because of this risk and the potential risk for heart disease, "I only recommend to my patients calcium in a natural form -- leafy green vegetables [the darker the green the better] and dairy products, as tolerated," Selinger said.
Coronary heart disease kills more than 370,000 Americans each year, according to the U.S. Centers for Disease Control and Prevention.
The study was published in the Oct. 10 issue of the Journal of the American Heart Association.