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

This was a randomized multicenter trial conducted at 11 academic medical centers and associated practices in the United States. Adults aged 45 to 75 years with at least one colorectal adenoma removed within 120 days before enrollment and no remaining polyps after complete colonoscopy were studied.

Participants took oral vitamin D3 1000 IU daily, calcium carbonate 1200 mg daily, both agents together, or matched comparators in a 2-by-2 factorial regimen. Treatment continued until the anticipated 3-year or 5-year surveillance colonoscopy; the active tablets were taken as two identical tablets daily.

Daily vitamin D3, calcium, or both did not significantly reduce recurrent colorectal adenomas or advanced adenomas in this population. For any adenoma, the adjusted risk ratio was 0.99 (95% CI, 0.89 to 1.09) for vitamin D versus no vitamin D and 0.95 (95% CI, 0.85 to 1.06) for calcium versus no calcium. Vitamin D plus calcium also showed no benefit versus calcium alone (risk ratio, 1.01; 95% CI, 0.88 to 1.15) or versus neither agent (risk ratio, 0.93; 95% CI, 0.80 to 1.08). Contingency-table comparisons were likewise nonsignificant: P = 0.98, P = 0.37, P = 0.79, and P = 0.49, respectively. Adverse events were few and not serious overall.

The vitamin D dose was relatively modest, which may have limited efficacy detection. Background supplementation with vitamin D and calcium was allowed later in the trial, and the report provides limited arm-specific dietary, physical activity, and BMI detail. Follow-up relied on scheduled surveillance colonoscopy over 3 to 5 years, so longer-term effects were not assessed.