Taking calcium supplements almost doubles the risk of heart attack, according to new research out of Europe, published in the June 2012 issue of the journal Heart. This finding comes two years after a meta-analysis out of New Zealand linked calcium supplements with an an elevated heart attack risk.

The study in Heart was based on nearly 24,000 residents of Heidelberg, Germany, who are part of a larger study called the European Prospective Investigation into Cancer and Nutrition Study, or EPIC. Researchers were looking at calcium and cardiovascular disease, or CVD, because some previous studies have suggested higher calcium intake may lower the rate of CVD risk factors, such as high blood pressure, type 2 diabetes and obesity. In this study, those who took calcium supplements – especially those who took calcium supplements only, and no other supplements – had an 86 percent higher risk of heart attack compared with people who did not take calcium supplements.

“[Calcium] intake from diet is important, but we should be more cautious about just using a pill instead of thinking about a more healthy, mixed diet,” says study co-author Sabine Rohrmann, PhD, MPH, head of the division of cancer epidemiology and prevention at the University of Zurich in Switzerland.

The researchers suggest calcium from supplements may be problematic for the cardiovascular system because it causes a spike in blood calcium levels, versus the gradual rise that occurs when calcium is obtained from food. And several other studies have linked high blood calcium levels with vascular calcification – basically, a buildup of calcium in blood vessels, which is a precursor to atherosclerosis and other cardiovascular diseases.

“[The] next important steps are to examine which mechanisms do promote the effects of elevated blood calcium levels,” says Rohrmann.

This study did not have information on the amount of calcium participants took. However, the New Zealand meta-analysis that linked calcium with heart attacks cited clinical trials where participants took 1,000 mg daily. Researchers agree more study is needed to determine whether a lower dosage is safer.
 

Millions of people depend on calcium supplements to keep osteoporosis at bay – especially people with rheumatoid arthritis and other inflammatory forms of the disease. For a variety of reasons, including corticosteroid use and limited activity, they are at increased risk of developing osteoporosis.

Reena L. Pande, MD, a cardiovascular specialist at Brigham and Women’s Hospital in Boston, says this is one of those situations in which it is important for patients to talk with their doctors. 

“Everyone is different,” Dr. Pande says. “For example, for a patient with osteoporosis, or with a specific condition that might be strongly linked with the development of osteoporosis, the benefit of calcium supplementation might outweigh the potential heart risk.”

But Ian Reid, MD, lead author of the New Zealand meta-analysis – which was published in the journal BMJ in April 2011 and looked at more than 29,000 women across 14 trials –  says many physicians may be unaware the evidence is “flimsy” when it comes to the benefits of calcium supplements on bones.

“In our last two meta-analyses, we carefully looked at the risk-benefit in women in their 60s and women in their mid-70s, and in both situations there are more cardiovascular events caused by calcium than there are fractures prevented by it,” says Dr. Reid, professor of medicine and endocrinology at the University of Auckland, New Zealand.

Dr. Reid, who wrote an editorial to accompany the new study, says evidence is growing that when it comes to getting enough calcium, food is the way to go. “I attended an international meeting on nutrition in osteoporosis in Switzerland two weeks ago, and I think it’s true to say that there was a consensus toward advocating dietary calcium in preference to supplements.”

Rohrmann says food seems not only to be a safer way to get calcium – but at a certain level it could actually be beneficial for cardiovascular disease. Her research in Heart found that getting moderately high amounts of calcium from food – 820 milligrams a day, about the amount in two eight-ounce containers of plain yogurt – had a 30 percent reduced risk of heart attack. Consuming much more – or less – than that did not appear to show a protective effect.

Dr. Pande says this latest study only reinforces her view that calcium is best obtained from food.

“Eating a well-rounded and balanced diet is always the most important way to get needed nutrients and vitamins,” she says. “The study was reassuring in that it did not indicate any increased risk for heart problems with dietary calcium intake.”

Dr. Pande says that while the study raises important issues and should be taken seriously, it isn’t perfect.

“It’s an observational study, not a randomized controlled trial, and you always have to take results from these kind of studies with a grain of salt. Furthermore, the numbers of events are small,” she says. Of the 23,980 people studied, only 354 had heart attacks during 11 years (average) of follow-up. “Nonetheless, the study raises the possibility that calcium supplements might increase risk of heart attacks. Further studies would be needed to know if this is indeed real or just an association.”