Tuesday, February 5, 2013

Are calcium supplements bad for the heart?

- Kenny Lin, MD

Until recently, the idea that calcium-containing supplements, which more than half of older adults in the U.S. consume regularly, could be harmful would have seemed absurd. Primary care clinicians have long recommended calcium supplements to reduce the risk of osteoporotic fractures in adults who are unable to meet the Institute of Medicine's Dietary Reference Intakes through diet alone. However, a large prospective study published this week in JAMA Internal Medicine demonstrated a statistically significant association between supplemental calcium (as opposed to dietary calcium) intake and a 20 percent higher relative risk of death from cardiovascular disease in men.

This troubling finding adds to the evidence base that suggests harmful cardiovascular effects of calcium-containing supplements. A timely pair of editorials in the February 1st issue of AFP debates the population-level risk of widespread calcium supplementation. Arguing that this potential risk should be a serious concern, Drs. Ian Reid and Mark Bolland review the results of their previous randomized trial and meta-analysis that found 20 to 30 percent increases in the incidence of acute myocardial infarction in adults taking calcium supplements. In their view, these adverse effects are not worth the potential benefits to bone health:

In both of our meta-analyses, calcium supplementation was more likely to cause vascular events than to prevent fractures. Therefore, the bolus administration of this micronutrient should be abandoned in most circumstances, and patients should be encouraged to obtain their calcium intake from an appropriately balanced diet. For those at high risk of fracture, effective interventions with a fully documented safety profile superior to that of calcium are available. We should return to seeing calcium as an important component of a balanced diet and not as a low-cost panacea to postmenopausal bone loss.

In the second editorial, Dr. Rajib Bhattacharya points out that the Women's Health Initiative and other randomized trials did not indicate that calcium supplements increased cardiovascular risk. He argues that secondary analyses of trials designed with other primary outcomes in mind may have predisposed these analyses to unforeseen bias, and that there is "no compelling evidence" that calcium supplements at usual doses pose dangers to heart health.

Notably, a draft recommendation statement released by the U.S. Preventive Services Task Force last June stated that there was insufficient evidence that vitamin D and calcium supplementation prevent fractures or cancer in otherwise healthy older adults. Although the only adverse effects of supplements mentioned in the Task Force's evidence review were renal and urinary tract stones, none of the reviewed studies were specifically designed to assess cardiovascular harms. Is it time to abandon routine calcium supplementation in healthy adults? If not, what additional evidence might make you change your practice?