A Trial of Calcium and Vitamin D for the Prevention of Colorectal Adenomas.

This was a multicenter randomized trial conducted at 11 academic medical centers and associated practices in the United States. Adults aged 45 to 75 with recently removed colorectal adenomas and no remaining polyps after colonoscopy were enrolled; active intervention arms included vitamin D3 (N=1024), calcium (N=762), and calcium plus vitamin D3 (N=643).

Participants received oral vitamin D3 1000 IU daily, calcium carbonate 1200 mg daily, or both together as two identical tablets daily. Treatment continued until the planned 3-year or 5-year colonoscopic examination; a 56 to 84 day run-in period was used to screen for adherence before randomization.

Daily vitamin D3, calcium, or their combination did not significantly reduce recurrent colorectal adenomas over 3 to 5 years. For one or more adenomas, the risk ratio was 0.99 (95% CI 0.89 to 1.09) for vitamin D vs no vitamin D, 0.95 (95% CI 0.85 to 1.06) for calcium vs no calcium, 1.01 (95% CI 0.88 to 1.15) for calcium plus vitamin D vs calcium alone, and 0.93 (95% CI 0.80 to 1.08) for calcium plus vitamin D vs neither agent. Advanced adenomas were also unchanged, with risk ratios of 0.99 (95% CI 0.75 to 1.29), 1.02 (95% CI 0.76 to 1.38), 0.89 (95% CI 0.63 to 1.26), and 0.99 (95% CI 0.63 to 1.56), respectively. The overall conclusion was that there was no clear evidence of benefit from either supplement alone or in combination.

The trial found null effects despite a relatively large sample, and subgroup signals were described as not robust and possibly due to chance. Background use of up to 1000 IU vitamin D and 400 mg calcium was allowed during the study, which could have diluted treatment effects. Findings apply to a selected population of adults 45 to 75 with prior adenomas and no residual polyps, so generalizability is limited.