Calcium supplements and cardiovascular risk: 5 years on

Abstract

Calcium supplements have been widely used by older men and women. However, in little more than a decade, authoritative recommendations have changed from encouraging the widespread use of calcium supplements to stating that they should not be used for primary prevention of fractures. This substantial shift in recommendations has occurred as a result of accumulated evidence of marginal antifracture efficacy, and important adverse effects from large randomized controlled trials of calcium or coadministered calcium and vitamin D supplements. In this review, we discuss this evidence, with a particular focus on increased cardiovascular risk with calcium supplements, which we first described 5 years ago. Calcium supplements with or without vitamin D marginally reduce total fractures but do not prevent hip fractures in community-dwelling individuals. They also cause kidney stones, acute gastrointestinal events, and increase the risk of myocardial infarction and stroke. Any benefit of calcium supplements on preventing fracture is outweighed by increased cardiovascular events. While there is little evidence to suggest that dietary calcium intake is associated with cardiovascular risk, there is also little evidence that it is associated with fracture risk. Therefore, for the majority of people, dietary calcium intake does not require close scrutiny. Because of the unfavorable risk/benefit profile, widespread prescribing of calcium supplements to prevent fractures should be abandoned. Patients at high risk of fracture should be encouraged to take agents with proven efficacy in preventing vertebral and nonvertebral fractures.

Keywords: Calcium supplements; cerebrovascular disease; ischemic heart disease; myocardial infarction; osteoporosis.

Figure 1.

Time to first event for myocardial infarction or stroke by treatment allocation in meta-analyses of five trials of calcium monotherapy (top panels) and in participants in the Women’s Health Initiative (WHI) calcium and vitamin D trial not using personal calcium supplements at randomization (bottom panels) [Bolland et al. 2010a, 2011b]. Note the different scales on the y and x axes. HR, hazard ratio; CI, confidence interval.

Figure 2.

Meta-analyses of the effect of calcium supplements with or without vitamin D on cardiovascular events [Bolland et al. 2011b]. The left panels show the time-to-first-event analyses and the right panels random effects models of trial-level summary data when complete trial-level data were available. HR, hazard ratio; CI, confidence interval.

Figure 3.

Number of prescriptions for calcium supplements per month in New Zealand from 2000 to 2013. The solid line is a smoothed average of the individual points (data provided by Robert Hipkiss, Ministry of Health, New Zealand).