–But the observational study suggested an overall benefit for dietary calcium.
A new observational study finds that calcium supplements may increase cardiovascular risk. By contrast, dietary calcium was linked to a protective effect.
Many people– in particular, older women– take calcium supplements to prevent or treat osteoporosis, though the supporting evidence for this use is quite thin. In recent years several studies have raised concerns that calcium supplements might be linked to increased CV risk. But the precise relationship between calcium– both from dietary sources and from supplements– and atherosclerosis has not been carefully studied in randomized trials.
In a paper published in the Journal of the American Heart Association, Erin Michos (Johns Hopkins) and colleagues analyzed data from more than 2,700 participants in the MESA (Multi-Ethnic Study of Atherosclerosis) study who did not have diagnosed CV disease. Among the 1,567 participants who had no coronary artery calcium at baseline, the group in the highest quintile of calcium intake (as assessed by a food questionnaire and medication inventory) had a significant 27% reduction in the development of CAC at ten years after adjustment for differences in baseline risk.
But the investigators found a potentially important difference in effect based on the calcium source. Calcium from supplements was associated with a 22% increase in the risk of CAC.
Any adverse effect of calcium supplements could have broad importance, since 43% of US adults take calcium supplements.
Instead of helping to promote bone health, the authors speculated that excessive doses of calcium might “accrue in vascular tissue.” But the authors warned that the study’s findings may not be a reflection of the effect of calcium but rather a broader demonstration of the “healthy user effect.” People who consumed large amounts of dietary calcium “may have been engaging in other unmeasurable health-promoting behaviors (ie, the healthy user effect), which could potentially explain why a decrease in risk of CAC development was observed in the highest quintile of calcium intake. Calcium-rich foods are associated with a healthy diet, and many of the participants with a high dietary calcium intake may be consuming vegetables, dairy, nuts, and fish—that provide cardioprotective benefits.” More generally, the authors cautioned in a press release that “their work only documents an association between calcium supplements and atherosclerosis, and does not prove cause and effect.”
In an interview, Michos wondered why so many people are taking calcium supplements. “The fracture data is not very compelling,” she noted. Besides the adverse CV effects suggested by her study, calcium supplements are also known to cause kidney stones, flatulence, and constipation. “People think that because they can get it over the counter there is no harm.”
Since “we saw no excess risk with diet, I tell my patients to take all their calcium through diet.”