A Cochrane review [Abstract] 1 included two studies with a total of 1,346 subjects. The doses of supplementary elemental calcium used were 1200 mg daily for a mean duration of 4 years, and 2000 mg/day for three years. The rates of loss to follow -up were 14 % and 11%. For the development of recurrent colorectal adenoma, a reduction was found (OR 0.74, CI 0.58,0.95) when the results from both trials were combined. Although the evidence suggests that calcium supplementation might contribute to a moderate degree to the prevention of colorectal adenomatous polyps, this does not constitute sufficient evidence to recommend the general use of calcium supplements to prevent colorectal cancer. No trial has directly demonstrated an effect of calcium supplementation on the development of colorectal cancer itself.
Comment: The quality of evidence is downgraded by study quality (inadequate or unclear allocation concealment) and by imprecise results (few outcome events).
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