New research suggests that calcium supplements may increase the risk of heart attack in healthy postmenopausal women.
Calcium supplementation is commonly prescribed to postmenopausal women to maintain bone health, and some data suggest that it might protect against vascular disease by lowering levels of bad cholesterol in the blood.
But evidence for this theory is lacking, so researchers at the University of Auckland investigated the effect of calcium supplementation on heart attack (myocardial infarction), stroke, and sudden death.
Their analysis involved 1,471 healthy postmenopausal women aged 55 years or over who had previously taken part 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. Heart attacks were more commonly reported in the calcium group. The occurrence of any three vascular events (heart attack, stroke or sudden death) was also more common in this group.
Because of the potential importance of these findings, the authors checked hospital admissions and reviewed all death certificates for study participants to identify any unreported events.
With these added events, heart attacks remained more common in the calcium group (36 events in 31 women versus 22 events in 21 women on placebo). Rates for heart attack, stroke or sudden death were also increased in this group (76 events in 60 women versus 54 events in 50 women on placebo) although these event rates were of borderline significance.
These findings are not conclusive, but suggest that high calcium intakes might have an adverse effect on vascular health and are concerning, say the authors. If confirmed by other studies, this effect could outweigh any beneficial effects of calcium on bone.
In the meantime, this potentially detrimental effect should be balanced against the likely benefits of calcium on bone, particularly in elderly women, they conclude.
This research was published January 16 on the British Medical Journal website.
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