Calcium has long been known to be important for maintaining healthy bones. Getting more of the mineral by taking calcium supplements seems like it should be a good thing. But some doctors aren’t so sure.
They point to growing—and often controversial—evidence that the calcium supplements many older adults take to prevent osteoporosis may increase their risk of heart disease.
The latest study links calcium supplements with an increased risk of atherosclerosis, which occurs when plaque builds up in the arteries, making them rigid and narrower, and setting the stage for serious heart and other vascular problems.
The study, in the October 2016 Journal of the American Heart Association, showed that the risk of developing new calcifications in the coronary (heart) arteries, a marker of atherosclerosis, was 22 percent higher in calcium supplement users compared with those who did not use supplements. There was no excess risk for high calcium intake when it was obtained from food sources alone.
Dietary calcium vs. a pill
In past studies, researchers have found a difference between how calcium from foods—including milk, other dairy products, and leafy green vegetables—affect the body when compared to supplements.
Some studies have shown an increased risk of heart attack and kidney stones among calcium supplement users. At the same time, calcium from food sources hasn’t been shown to increase heart attack risk and may actually lower the risk of kidney stones.
Some scientists suspect that because people who take supplements often ingest relatively high doses of calcium at a single time, calcium levels build up in the blood or vascular tissue, ultimately becoming high enough to cause adverse effects. The body may also metabolize calcium from diet and supplements differently.
“Our study supports the idea that increased risk may depend on the calcium source rather than the total amount,” says Erin Michos, M.D., the study’s lead author and the director of preventive cardiology at the Ciccarone Center for the Prevention of Heart Disease at Johns Hopkins University School of Medicine in Baltimore. “In fact, those with the highest risk in the study were supplement users with the lowest overall calcium intake.”
Michos and her team primarily focused on the medical records of 1,500 individuals, ages 45 to 84, who had no or insignificant evidence of heart disease. Over 10 years, dietary calcium intake appeared to have a protective effect on the participants’ arteries, whereas calcium supplements were associated with the opposite effect: a 22 percent increased risk of plaque buildup.
The study relied on the recall of participants reporting on their calcium intake. Because of the study’s observational nature, the researchers were unable to prove a direct cause-and-effect relationship between calcium supplements and atherosclerosis.
Support for supplements
Evidence that calcium supplementation is associated with heart disease isn’t conclusive. Newly released guidelines from the National Osteoporosis Foundation and the American Society for Preventive Cardiology says that calcium with or without vitamin D (which helps your body absorb calcium), either from food or supplements, is considered safe for the heart if it doesn’t exceed the daily limit of 2,000 milligrams (mg) for men or 2,500 mg for women.
The guidelines did not find a significant association—positive or negative—between calcium and heart health. Nor did they find any evidence that more calcium beyond the recommended daily amounts is better. The guideline does acknowledge that obtaining calcium from food is preferred, with supplements filling the gap only when needed.
“If you’re worried about bone health, it’s smart to get calcium from the foods you eat, such as leafy green vegetables and low fat dairy sources,” Michos says. Consult a doctor knowledgeable about the latest calcium research, she adds, who can help you decide whether to add a supplement.
Melissa Caravella is a New Jersey-based health writer and content strategist. She has spent more than a dozen years writing and editing health content for consumers, with a focus on translating complex medical information into understandable and actionable knowledge.