Calcium supplementation may make older women susceptible to heart attacks, according to a study.
This finding runs counter to the suggestion that calcium supplementation, commonly prescribed to postmenopausal women to maintain bone health, may prevent vascular disease by lowering levels of bad cholesterol in the blood.
University of Auckland researchers investigated the effect of calcium supplementation on heart attack (myocardial infarction), stroke, and sudden death.
They involved 1,471 healthy postmenopausal women, aged 55 years and above, in their analysis. All the subjects had previously participated in a study to assess the effects of calcium on bone density and fracture rates.
The women were randomly allocated to a daily calcium supplement or placebo. Dietary calcium intake was assessed and women were seen every six months over five years. Adverse events were recorded at each visit.
It was observed that heart attacks were more commonly reported in the calcium group. The occurrence any of the three vascular events heart attack, stroke or sudden death was also more common in this group.
The authors also checked hospital admissions, and reviewed all death certificates, for study participants to identify any unreported events.
The whole process revealed that heart attacks remained more common in the calcium group than the placebo group. Rates for heart attack, stroke or sudden death were also increased in this group, although these event rates were of borderline significance.
The study's authors admit that the findings are not conclusive. The results, however, suggest that calcium intakes might have an adverse effect on vascular health, they say.
Should other studies confirm these findings, this effect may outweigh any beneficial effects of calcium on bone, reports the British Medical Journal (BMJ).
For the time being, the authors say, this potentially detrimental effect should be balanced against the likely benefits of calcium on bone, particularly in elderly women.