Bolland MJ et al. (2008) Vascular events in healthy older women receiving calcium supplementation: randomised controlled trial. BMJ [doi:10.1136/bmj.39440.525752.BE]

Calcium supplementation in healthy, postmenopausal women acutely elevates serum calcium levels, and increases the HDL:LDL cholesterol ratio. Evidence exists that a high calcium intake might also reduce cardiovascular event rates. Bolland and colleagues accordingly investigated whether calcium supplementation influenced myocardial infarction, stroke, and sudden death rates in a preplanned secondary analysis of data from the Auckland calcium study (a randomized, controlled trial designed primarily to assess the effects of calcium supplementation on bone density and fracture incidence).

Healthy, postmenopausal women (aged >55 years) were randomly allocated to receive placebo (n = 739) or supplementation with 1 g elemental calcium (n = 732), taken as two tablets before breakfast and three in the evening. The women were followed up every 6 months for 5 years; tablet counts and validated questionnaires were used to assess compliance with treatment and dietary calcium intake.

Surprisingly, cardiovascular event rates were significantly increased (P = 0.008) in the calcium-supplementation group. Not only was this effect strongest in the most treatment-compliant women, the greatest increases occurred during the second half of follow-up. This pattern implies that vascular damage occurs before event rates increase. The authors note that the beneficial effects of calcium supplementation on bone loss would be rapidly outweighed by increased cardiovascular event rates (e.g. the 5-year number needed to treat to cause one stroke was 56, whereas the number needed to treat to prevent one symptomatic fracture was 50). Although not definitive, the authors' conclusions flag cardiovascular health as an area of concern in relation to calcium supplementation.