A randomized, double-blind, placebo-controlled trial has analyzed the potential benefit of supplementation with vitamin D, calcium or both in the prevention of colorectal adenomas. A cohort of 2,259 participants with recently diagnosed and removed adenomas received daily vitamin D3 (1,000 IU), calcium as carbonate (1,200 mg) or both with follow-up colonoscopies 3 or 5 years after the start of the therapy. The reduced risk of recurrent colorectal adenoma was not statistically significant under this regimen and few serious adverse events were reported.