Should we prescribe calcium supplements for osteoporosis prevention?

Abstract

Advocacy for the use of calcium supplements arose at a time when there were no other effective interventions for the prevention of osteoporosis. Their promotion was based on the belief that increasing calcium intake would increase bone formation. Our current understandings of the biology of bone suggest that this does not occur, though calcium does act as a weak antiresorptive. Thus, it slows postmenopausal bone loss but, despite this, recent meta-analyses suggest no significant prevention of fractures. In sum, there is little substantive evidence of benefit to bone health from the use of calcium supplements. Against this needs to be balanced the likelihood that calcium supplement use increases cardiovascular events, kidney stones, gastrointestinal symptoms, and admissions to hospital with acute gastrointestinal problems. Thus, the balance of risk and benefit seems to be consistently negative. As a result, current recommendations are to obtain calcium from the diet in preference to supplements. Dietary calcium intake has not been associated with the adverse effects associated with supplements, probably because calcium is provided in smaller boluses, which are absorbed more slowly since they come together with quantities of protein and fat, resulting in a slower gastric transit time. These findings suggest that calcium supplements have little role to play in the modern therapeutics of osteoporosis, which is based around the targeting of safe and effective anti-resorptive drugs to individuals demonstrated to be at increased risk of future fractures.

Keywords: Calcium; Fractures bone; Myocardial infarction; Osteoporosis.

Fig. 1

Meta-analysis of the effects of calcium alone or with vitamin D, on hip fracture risk in randomised controlled trials. Studies have been divided according to the residential status of their participants. The classification of the Harwood study is debatable since subjects were in hospital following fractures at trial entry, though most had been community dwelling previously. [Reprinted from "Calcium risk.benefit updated.New WHI analyses", by Reid, IR, Bolland, MJ, 2013, Maturitas, 77(1), pp. 1-3. Copyright 2013 by the Elsevier. Reprinted with permission].

Fig. 2

Kaplan.Meier survival curves for time to incident myocardial infarction or stroke by treatment allocation in a meta-analysis of patient-level data from five trials of calcium supplements used as monotherapy (n=8,151) and in women in the Women's Health Initiative (WHI) calcium and vitamin D trial not using personal calcium supplements at randomization (n=16,718). The magnitude and time-course of the effects of calcium supplements on the two classes of vascular events were very similar in these independent databases. CI, confidence interval; HR, hazard ratio. [Reprinted from "Subgroup analysis for the risk of cardiovascular disease with calcium supplements", by Radford LT, Bolland MJ, Gamble GD, Grey A, Reid IR, 2013, Bonekey Rep, 77(1), pp. 1-3. Copyright 2013 by the Nature Publishing Group. Reprinted with permission].

Fig. 3

The association of serum calcium, phosphate, and calcium.phosphate product (CPP) with the presence of coronary artery disease, divided into calcified or mixed plaque, and non-calcified plaque. Plaque was measured by cardiac computed tomography in 7553 Korean adults. [Reprinted from "Impact of serum calcium and phosphate on coronary atherosclerosis detected by cardiac computed tomography", by Shin S, Kim KJ, Chang HJ, Cho I, Kim YJ, Choi BW, Rhee Y, Lim SK, Yang WI, Shim CY, Ha JW, Jang Y, Chung N, 2012, Eur Heart J, 33(22), pp.2873-81. Copyright 2012 by the Oxford University Press. Reprinted with permission].