BMJ  2008;336:403-404 (23 February), doi:10.1136/bmj.39493.418704.1F

Letters

Calcium supplementation

Confounders were ignored

The first 150 words of the full text of this article appear below.

Bolland et al did not control for vitamin D concentrations during their study but said only that the women with serum 25-hydroxyvitamin D concentrations below 25 nmol/l were excluded.¹ This implies that serum concentrations of vitamin D were not monitored during the study. This is important because, according to the results of the Framingham offspring study, low serum concentrations of vitamin D are strictly associated with an increase in vascular risk² and may impair calcium absorption.²

Two important confounding factors are not controlled for—consumption of non-steroidal anti-inflammatory drugs and analgesics and previous hormone replacement therapy. These two potent confounders may completely reverse the results and also interact with each other on cardiovascular risk.^{3 4 5}

To consider the self reported events separately from those unreported but taken from the national database of hospital admissions is surprising. When self reported and unreported events are considered together the differences between calcium and placebo group . . . [Full text of this article]

¹ Promed Galileo Medical Society, Pisa 56011, Italy

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Relevant Article

Vascular events in healthy older women receiving calcium supplementation: randomised controlled trial

Mark J Bolland, P Alan Barber, Robert N Doughty, Barbara Mason, Anne Horne, Ruth Ames, Gregory D Gamble, Andrew Grey, and Ian R Reid
BMJ 2008 336: 262-266. [Abstract] [Full Text] [PDF]