New Guideline Gives the Greenlight to Calcium Supplements

Calcium intake—whether from food or supplements—has no bearing on the cardiovascular risk of otherwise healthy adults, according to experts backed by the National Osteoporosis Foundation and American Society for Preventive Cardiology. So long as individuals don’t exceed 2,000 to 2,500 mg per day, calcium “should be considered safe” from this standpoint, they assert.

That conclusion, based on a review of the evidence conducted by researchers at Tufts University (Boston, MA) and the RAND Corporation (Santa Monica, CA), is the main message of a new clinical guideline released by the two nonprofit groups. Both the recommendations and the review were published online earlier this week in the Annals of Internal Medicine.

Asked about how these conclusions gel with ongoing hints of CV risk accompanying calcium intake, guideline co-author Taylor C. Wallace, PhD (George Mason University, Fairfax, VA), told TCTMD: “There is a lot of misinformation out there.

“There is a very large body of evidence . . . showing the safety of calcium in the cardiovascular system,” said Wallace, who recently outlined his views online. “Even at levels above the tolerable upper intake level set by the National Academy of Sciences you don’t really see any adverse effect.” While there have been some studies suggesting risk, many were conducted decades ago when lifestyles were different, he said. Observational studies have inherent limitations, and some of the evidence stems from randomized trials originally designed to test other hypotheses and endpoints.

“So you have to ask yourself, in nutrition, is this slight little increased risk actually true, or is there just some confounding in there? I think in many of these population studies, they might control for the top six risk factors for cardiovascular disease, but there are over 200 that we know of that they’re not controlling for. So I would take data like that very lightly,” Wallace stressed. “Our data compiles all of the population studies, all of the clinical research. The outcome from each of those bodies of data really shows that calcium supplements are extremely safe and just have no benefit or no detriment to the cardiovascular system.”

One certainty, Wallace said, is that “calcium is essential for bones.” With dairy consumption on the decline, it may be hard for many people to get enough calcium through diet. “It’s a real public health concern, especially in postmenopausal women. Because women start getting rid of their calcium supplements and they’re not consuming three servings of dairy per day, they’re putting themselves at an increased risk for fractures.”

Asked about the strength of the evidence in this regard, he said, calcium supplementation “is probably one of the strongest nutrition interventions that we have today.”

Why Take a Chance?

Erin D. Michos, MD, MHS (Johns Hopkins University School of Medicine, Baltimore, MD), however, described the evidence on fracture as “not very clear.”

Why take on any uncertainty in terms of safety, she asked, when there is no clear benefit to calcium supplements? Earlier this month in the Journal of the American Heart Association, Michos and colleagues published an analysis based on observational data from the Multi-Ethnic Study of Atherosclerosis showing that CVD-free adults who took supplements were 22% more likely to develop atherosclerosis by 10 years.

Commenting on the Annals papers for TCTMD, she said that “one thing that’s really consistent is this meta-analysis . . . , along with our recent study, continues to show the lack of cardiovascular harm with dietary calcium alone.” This should be “reassuring,” she noted, for those individuals who get their calcium from leafy greens, dairy, and other food sources.

Importantly, Michos stressed, there’s no evidence of a dose response, meaning that adding more calcium on top of the recommended daily allowance of 1,000 mg for men and 1,200 for women ages 51 and older isn’t any more helpful for bone health.

As for supplements, Michos found the current review unpersuasive, since the data on this topic were derived mostly from observational studies and researchers only analyzed those reporting the dose. “So for that reason, some potential relevant studies were not included,” Michos said, giving the 2012 EPIC-Heidelberg study as an example. Moreover, there was no meta-analysis of randomized trials, since these were considered “too heterogenous,” she pointed out. “Clinical trials are our best evidence, not observational studies.” This is true, she said, despite the fact that the randomized trials to date were initially not designed to test cardiovascular outcomes.

“But even if we said, ok, let’s give it the benefit of the doubt: there’s no harm with calcium supplements for cardiovascular disease,” Michos said. “The real question we should be asking is whether there is going to be any benefit to support their use. Because they’re not free of side effects,” which can include bloating, constipation, and kidney stones. Meanwhile, “their benefit on fracture reduction is not very clear,” Michos continued, noting that randomized trial data in this area are “weak and inconsistent,” with the US Preventative Services Task Force saying there was insufficient evidence to recommend either for or against supplements.

Low Dose Can Meet Daily Needs

An editorial accompanying the Annals papers, by Karen L. Margolis, MD, MPH (HealthPartners Institute, Minneapolis, MN), and JoAnn E. Manson, MD, DrPH (Brigham and Women’s Hospital, Boston, MA), describes the question over CV risk and supplementation an “area of particular controversy,” one that is important given how many people take vitamins that include calcium.

“How should clinicians and patients respond to the limited and imperfect evidence regarding the relationship between calcium supplements and cardiovascular risk? Although the preponderance of evidence does not support cardiovascular adverse effects, dietary sources of calcium are preferable to supplements for other reasons,” such as kidney stones, they agree.

Median dietary calcium intake for US adults is around 700 to 1,000 mg per day, Margolis and Manson report, adding, “Supplements can be used to make up but not exceed the gap between dietary intake and the recommended intake level; however, most persons require no more than 500 mg of supplemental calcium to meet their daily needs, if not met by diet alone.”