No evidence for posttreatment effects of Vitamin D and calcium supplementation on risk of colorectal adenomas in a randomized trial

Vitamin D and calcium supplementation are postulated to have chemopreventive effects against colorectal neoplasia, yet in our previously reported randomized trial, there was no overall efficacy of calcium and/ or vitamin D₃ against colorectal adenoma recurrence. It is possible vitamin D₃ and calcium chemopreventive effects are not detectable until beyond the 3- to 5-year follow-up captured in that trial. Accordingly, we explored possible vitamin D and calcium effects on posttreatment (observational) adenoma occurrence. In this secondary analysis of the observational follow-up phase of the Vitamin D/Calcium Polyp Prevention Study, participants who completed the treatment phase were invited to be followed for one additional surveillance colonoscopy cycle. We evaluated adenoma occurrence risk at surveillance colonoscopy, with a mean of 55 15 months after treatment follow-up, according to randomized treatment with vitamin D versus no vitamin D, calcium versus no calcium, and calcium plus vitamin D versus calcium alone. Secondary outcomes included advanced and multiple adenomas. Among the 1,121 participants with observational follow-up, the relative risk (95% confidence interval, CI) of any adenoma was 1.04 (0.93–1.17) for vitamin D versus no vitamin D; 0.95 (0.84–1.08) for calcium versus no calcium; 1.07 (0.91–1.25) for calcium plus vitamin D versus calcium; and 0.96 (0.81–1.15) for calcium plus vitamin D versus neither. Risks of advanced or multiple adenomas also did not differ by treatment. Our results do not support an association between supplemental calcium and/or vitamin D₃ for 3 to 5 years and risk of recurrent colorectal adenoma at an average of 4.6 years after treatment.