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 elsewhere conclude that taking Calcium in the form of supplements may raise the risk of plaque buildup in arteries and heart damage, although a diet high in calcium-rich foods appears be protective.
In a report on the research, published in the Journal of the American Heart Association ( JAHA ), the researchers caution that their work only documents an association between Calcium supplements and atherosclerosis, and does not prove cause and effect.
But they say the results add to growing scientific concerns about the potential harms of supplements, and they urge a consultation with a knowledgeable physician before using Calcium supplements.
An estimated 43% of American adult men and women take a supplement that includes Calcium, according the National Institutes of Health.
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 ( NHLBI ), which included more than 6,000 people seen at six research universities, including Johns Hopkins.
The study focused on 2,742 of these participants who completed dietary questionnaires and two CT ( computed tomography ) scans spanning 10 years apart.
The participants chosen for this study ranged in age from 45 to 84, and 51% were female. Forty-one percent were white, 26% were African-American, 22% were Hispanic and 12% 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, like cereals; and other Calcium-rich foods.
Separately, the researchers inventoried what 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% 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% less likely than the 20% of participants with the lowest calcium intake ( less than 400 milligrams of daily calcium ) to develop heart disease, as indicated by their coronary artery calcium test.
Next, the investigators focused on the differences among those taking in 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% 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. 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 ( over 1,022 milligrams per day ) there was no increase in relative risk of developing heart disease over the 10-year study period. ( Xagena )
Source: Johns Hopkins Medicine. 2016