Taking calcium in the form of supplements may raise the risk of plaque buildup in arteries and heart damage, while a diet high in calcium-rich foods does not, say researchers at Johns Hopkins Medicine.
The researchers caution that their work only documents an association between calcium supplements and atherosclerosis; it 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.
"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 one of the researchers. These findings, however, add to the body of evidence that excess calcium in the form of supplements may harm the heart and vascular system.
About the study
The researchers were motivated to look at the effects of calcium on the heart and vascular system because studies already showed that, when consumed, 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 body's main blood vessel, the aorta and other arteries, impeding blood flow and increasing the risk of heart attack.
For the study, the research team followed 2,742 multi-ethic men and women, aged 45 to 84, for 10 years to determine if calcium – from diet or supplements – was linked to coronary artery calcification (CAC), an early sign of heart disease.
CAC is a buildup of calcium in fatty plaques in the heart’s artery walls. It’s measured using a special x-ray test called computed tomography (CT scan). The test can show whether you’re at risk for heart attack before other symptoms occur.
At the onset of the study, researchers assessed participants’ diets over the previous year as well as their use of calcium supplements. At the beginning of the study, and again after 10 years, their CAC was measured using a CT scan.
Supplement-only users more likely to have signs of heart disease
The risk of developing calcified coronary arteries over 10 years was 22 per cent higher in adults who took calcium supplements than those who did not. That was true after taking into account daily calorie intake, body weight, exercise, smoking, alcohol intake and other risk factors for heart disease.
The highest risk for plaque buildup was found among supplement users who consumed the least calcium from their diet. Conversely, the lowest risk was observed in people who didn’t take supplements but consumed the most calcium from diet.
Calcium from foods did not increase heart risk
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.
It’s thought that a high intake calcium in a single dose from supplements can cause a transient elevated blood calcium level which, in turn, can lead to calcium depositing in artery walls. Over time, calcified fatty plaques can harden and narrow blood vessels, hindering blood flow to the heart.
Excess blood calcium may also influence inflammation, insulin activity and body weight regulation, other factors that could accelerate hardening of arteries.
Dietary calcium is believed to be metabolized differently than calcium in supplements. Unlike high dose supplements, calcium in foods is absorbed into the bloodstream in smaller amounts throughout the day.
My advice: With potential for harm and inconclusive benefits to bone health, it’s prudent to be cautious about supplementing with calcium. Particularly so when studies have consistently found no increased risk of heart problems from consuming calcium from foods.
Meet your daily calcium requirement from dietary sources, preferably.
All research on this web site is the property of Leslie Beck Nutrition Consulting Inc. and is protected by copyright. Keep in mind that research on these matters continues daily and is subject to change. The information presented is not intended as a substitute for medical treatment. It is intended to provide ongoing support of your healthy lifestyle practices.