October 12, 2016
After analyzing 10 years of medical tests on more than 2,700 people in a federally funded heart disease study, researchers at Johns Hopkins Medicine and The University of North Carolina at Chapel Hill conclude that taking supplemental calcium may raise the risk of plaque buildup in arteries and cause heart damage. A diet high in calcium-rich foods appears be protective, however.
John Anderson, PhD, professor emeritus of nutrition at UNC’s Gillings School of Global Public Health, is a study co-author.
In a report on the research, published online Oct. 11 in the Journal of the American Heart Association, the researchers caution that their work only documents an association between calcium supplements and atherosclerosis and does not prove cause and effect.
The results add to growing scientific concerns about the potential harms of supplements, the researchers say, and they urge people to consult with a knowledgeable physician before using calcium supplements. An estimated 43 percent of American adult men and women take a supplement that includes calcium, according to the National Institutes of Health.
“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 Erin Michos, MD, MHS, associate director of preventive cardiology and associate professor of medicine at Johns Hopkins University School of Medicine’s Ciccarone Center for the Prevention of Heart Disease. “But our study adds to the body of evidence that excess calcium in the form of supplements may harm the heart and vascular system.”
The researchers were motivated to look at the effects of calcium on the heart and vascular system, as studies already showed, in Anderson’s words, that “ingested calcium supplements — particularly in older people — don’t make it to the skeleton or get completely excreted in the urine, so they must be accumulating in the body’s soft tissues.” Scientists also knew that as a person ages, calcium-based plaque builds up in the aorta, the body’s main blood vessel, and other arteries, impeding blood flow and increasing the risk of heart attack.
The investigators looked at detailed information from the Multi-Ethnic Study of Atherosclerosis, a long-running research project funded by the National Heart, Lung and Blood Institute, which included more than 6,000 people seen at six research universities. Their study focused on 2,742 of these participants who completed dietary questionnaires and two CT scans spanning 10 years apart.
The participants chosen for the study ranged in age from 45 to 84, and 51 percent were female. Forty-one percent were white, 26 percent were African-American, 22 percent were Hispanic and 12 percent were Chinese. At the study’s onset in 2000, all participants answered 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 (such as cereals) and other calcium-rich foods.
Separately, the researchers inventoried which drugs and supplements each participant took on a daily basis. The investigators used cardiac CT scans to measure participants’ coronary artery calcium scores, a measure of calcification in the heart’s arteries and a marker of heart disease risk when the score is above zero. Initially, 1,175 participants showed plaque in their heart arteries. The coronary artery calcium tests were repeated 10 years later to assess newly developing or worsening coronary heart disease.
For the analysis, the researchers first split the participants into five groups based on their total calcium intake, including both calcium supplements and dietary calcium. After adjusting the data for age, sex, race, exercise, smoking, income, education, weight, smoking, drinking, blood pressure, blood sugar and family medical history, the researchers separated out 20 percent of participants with the highest total calcium intake, which was greater than 1,400 milligrams of calcium a day. That group was found to be on average 27 percent less likely than the 20 percent of participants with the lowest calcium intake — fewer than 400 milligrams of daily calcium — to develop heart disease, as indicated by their coronary artery calcium test.
Next, the investigators focused upon the differences among those consuming only dietary calcium and those using calcium supplements. Forty-six percent of their study population used calcium supplements.
The researchers again accounted for the same demographic and lifestyle factors that could influence heart disease risk, as in the previous analysis, and found that supplement users showed a 22 percent increased likelihood of having their coronary artery calcium scores rise higher than zero over the decade, 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,” said Anderson. “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.”
Among participants with highest dietary intake of calcium — more than 1,022 milligrams per day — there was no increase in relative risk of developing heart disease over the 10-year study period.
“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,” said Michos. “But patients really should discuss any plan to take calcium supplements with their doctor to sort out a proper dosage or whether they even need them.”
According to the U.S. Centers for Disease Control and Prevention, coronary heart disease kills more than 370,000 people each year in the U.S. More than half of women over 60 take calcium supplements — many without the oversight of a physician — because they believe it will reduce their risk of osteoporosis.
Other authors on the study included Bridget Kruszka, MPH, research scientist, and Joseph Delaney, PhD, research assistant professor of epidemiology at the University of Washington; Ka He, ScD, professor and chair of epidemiology and biostatistics at Indiana University-Bloomington (formerly at UNC Gillings School), Gregory Burke, MD, professor of public health sciences in the Wake Forest University School of Medicine; Alvaro Alonso, MD, PhD, associate professor of epidemiology at Emory University’s Rollins School of Public Health; Diane Bild, MD, MPH, associate director for science at the Patient-Centered Outcomes Research Institute; and Matthew Budoff, MD, professor of medicine at the UCLA Medical Center.
The study was funded by grants from the National Heart, Lung and Blood Institute, National Center for Research Resources, National Institute of Neurological Disorders and Stroke, and the Blumenthal Scholars Award in Preventive Cardiology.