Updated: 10 September 2010

A recent publication by Bolland et al published in the British Medical Journal suggests that calcium supplements may increase the relative risk of ischaemic heart disease by 30%.¹

While it is important to investigate possible harm caused by dietary supplements, it is difficult to know how much weight to put on this meta-analysis for several reasons. Firstly, a similar study – i.e. a pooled analysis of several randomized controlled trials where calcium supplements were given, funded by the American Heart Association did not detect any statistically significant increased risk of cardiovascular disease or other negative effects of calcium supplements.² Secondly, none of the individual randomized trials analysed reported a statistically significant increased risk of ischaemic heart disease. Thirdly, new data from Lewis et al also reported no increase in atherosclerotic vascular disease related events in elderly women receiving calcium supplements (1200mg per day) followed for a total of 9.5 years (5 years on calcium supplements and a further 4.5 years). Importantly, records in this study, but not in most others, were validated through hospital admission data linkage although data for myocardial infarction events were not reported separately³. Fourthly, previous observational studies examining data from very large numbers of people have shown no adverse effect of high calcium intakes. As pointed out by Bolland et al, the effect of high dietary calcium intakes from diet were not studied in their recent meta-analysis.

While these studies were negative, it is important to recognise that methodological issues in the individual trials would have resulted in lack of power to detect a deleterious effect of calcium supplementation if there really was one present. For example, compliance in most, if not all the large trials, was around 50% so that a deleterious effect of calcium might have been missed. In post hoc analysis, the reduction in sample size when only compliers are examined, reduces the power of the study. Furthermore, none of the trials with calcium supplements were designed to investigate vascular events, so that randomization may have produced an uneven distribution of risk factors for cardiovascular disease, which could produce spurious results in either direction. In most of the studies, the subjects were not dietary calcium deficient, so supplements were given to people who already had adequate calcium intakes from dietary sources. In some studies, total calcium intakes were above 2000mg/day.

Given these uncertainties, ANZBMS recommends achieving a total calcium intake of 1000-1300mg, depending on age and sex, where possible through dietary intake of calcium rich foods. Similar recommendations come from the National Health and Medical Research Council. If dietary intake is not feasible and the treating doctor believes calcium supplements are needed for fracture risk reduction, then calcium supplements in doses of 500-600mg can be considered after a discussion of their benefits vs risks.

1. Bolland MJ, Avenell A, Baron JA, Grey A, MacLennan GS, Gamble GD, Reid IR. Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. BMJ 2010; 341:c3691.

2. Wang L, Manson JE, Song Y, Sesso HD. Systematic review: Vitamin D and calcium supplementation in prevention of cardiovascular events. Ann Intern Med. 2010 Mar 2;152(5):315-23.

3. Lewis JR, Calver J, Zhu K, Flicker L, Prince RL. Calcium supplementation and the risks of atherosclerotic vascular disease in older women: results of a 5-year RCT and a 4.5-year follow-up. J Bone Miner Res. 2010 Jul 7. [Epub ahead of print].

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