Do calcium supplements increase the risk of heart disease? Research findings over the past few years have gone back and forth like the proverbial ping-pong ball—yes, no, yes, no. Last October a widely reported study in the Journal of the American Heart Association (JAHA) once again suggested there’s a link between the supplements and heart disease. But then, in December 2016, new guidelines from the National Osteoporosis Foundation and the American Society for Preventive Cardiology basically said not to worry. No wonder some of our readers have expressed their confusion.
The story goes back to 2010-11, when researchers in New Zealand published two analyses of previous studies, which suggested that calcium supplements could increase the risk of heart attacks. Many experts in the field questioned these analyses, and the Wellness Letter critiqued their methodology (see Can Calcium Pills Hurt Your Heart?). Despite these limitations, however, we said that the concerns called for further research.
Since then, observational studies and clinical trials have yielded inconsistent, though mostly reassuring, results about the safety of calcium supplements. Some have even linked calcium (from food or supplements) to lower coronary risk.
For instance, in a large Canadian study in the Journal of Clinical Endocrinology & Metabolism in 2013, women who took up to 1,000 milligrams of calcium a day had a 22 percent lower death rate over a 10-year period than nonusers. There was no significant effect on mortality rates in men or with higher doses of calcium. In contrast, a study by the American Cancer Society in 2016 found that supplemental calcium was associated with a lower all-cause mortality rate in women, but that high doses (at least 1,000 milligrams a day) were linked to higher mortality rate in men.
An observational study of 75,000 female nurses in Osteoporosis International in 2014 also linked calcium supplements to a reduced risk of heart attacks. Women who took 1,000 milligrams or more of calcium a day had a 29 percent lower risk of heart attack over a 24-year period than nonusers. Also in 2014, a meta-analysis in the Journal of Bone and Mineral Research pooled data from 18 clinical trials and concluded that calcium supplements, with or without vitamin D, do not increase the risk of coronary artery disease, notably heart attacks.
What happens in coronary arteries?
One long-time concern has been that calcium from food and supplements could build up in coronary arteries (coronary calcification) and contribute to atherosclerosis. In recent years, however, several studies found no such association between calcium intake and coronary calcification. A 2012 analysis from the long-running Framingham Offspring Study concluded that people who consume the most calcium from food and/or supplements, as much as 3,000 milligrams a day, do not have more coronary calcium. This was confirmed by an analysis from the Diabetes Heart Study in 2014, which found no association between calcium intake (from diet or supplements) and coronary calcification. In fact, calcium supplements were associated with reduced mortality rates in women (there was no significant effect in men).
The new JAHA study raised the issue again. Somewhat confusingly, it found that while people who consumed the most calcium (more than 1,450 milligrams from food and supplements) had the lowest risk of coronary calcification, those who got their calcium mostly from pills were actually at elevated risk.
The new guidelines from the two expert groups seem to settle the issue, at least for now. They were based on a systematic analysis, which found that calcium from food or supplements—up to 2,500 milligrams a day, more than double the recommended intake (data on higher intakes are lacking)—is not associated with coronary risk in healthy people. And they said there’s “no established biological mechanism” linking calcium intake to cardiovascular disease.
“Obtaining calcium from food sources is preferred [but] supplemental calcium can be safely used to correct any shortfalls in intake,” the guidelines concluded. “Discontinuation of supplemental calcium for safety reasons is not necessary and may be harmful to bone health when intake from food is suboptimal.”
It’s best to get calcium from your diet because foods naturally rich in calcium supply many nutrients important for bones and general health. In addition, high doses of calcium supplements increase the risk of the most common type of kidney stones in some people, while foods naturally rich in calcium (notably dairy products) protect against stones. If you can’t get the recommended 1,000 to 1,200 milligrams of calcium a day from diet alone, you may need only a small amount of supplemental calcium to fill the gap. More is not necessarily better.
Also see 8 Key Facts About Milk.