Calcium linked to increase in MI in older women
Calcium supplements are taken by many postmenopausal women to reduce the risk of fractures. It has also been suggested that calcium may reduce cardiovascular risk by lowering lipids and blood pressure.
This study, a secondary analysis of a trial originally designed to assess the effects of calcium on bone density and fracture rates, has found that calcium supplements may increase the risk of cardiovascular events.
The study included 1,471 healthy postmenopausal women with a mean age of 74. Women were randomised to either calcium supplementation (732) or placebo (739) and followed up for five years. Adverse cardiovascular events were recorded, including death, chest pain, MI, stroke, transient ischaemic attack, and a composite end point of MI, stroke, chest pain or sudden death.
Self-reported events were verified and MI was found to be significantly more common in women taking calcium (relative risk 2.12, 95% CI 1.01-4.47, P=0.047).
The composite endpoint was also more common in patients taking calcium, with a relative risk of 1.47, although this was not significant.
When unreported events were added using data from the New Zealand database of hospital admissions, the relative risks of both MI and the composite endpoint were still higher in patients on calcium compared with placebo, although neither was statistically significant. Similarly, the relative risk of stroke was higher in patients on calcium compared with placebo, although this was not statistically significant (relative risk 1.37, 95% CI 0.83-2.28, P=0.23).
Although this study was a secondary analysis and the cardiovascular event rate was relatively low, the findings are surprising. There appears to be a trend of increased cardiovascular events in postmenopausal women taking calcium, which could offset its protective effects on bone.
This study should provide food for thought when considering calcium supplementation in postmenopausal women at low risk of fracture or with established cardiovascular disease until more conclusive evidence is available.
Bolland MJ, Barber PA, Doughty RN et al. Vascular events in healthy older women receiving calcium supplementation: randomised controlled trial. BMJ 2008 doi:10.1136/bmj.39440.525752.BEReviewer
Dr Peter Savill
GPwSI Cardiology, Southampton