RT Journal Article SR Electronic T1 Calcium and vitamin D supplementation and increased risk of serrated polyps: results from a randomised clinical trial JF Gut JO Gut FD BMJ Publishing Group Ltd and British Society of Gastroenterology SP 475 OP 486 DO 10.1136/gutjnl-2017-315242 VO 68 IS 3 A1 Seth D Crockett A1 Elizabeth L Barry A1 Leila A Mott A1 Dennis J Ahnen A1 Douglas J Robertson A1 Joseph C Anderson A1 Kristen Wallace A1 Carol A Burke A1 Robert S Bresalier A1 Jane C Figueiredo A1 Dale C Snover A1 John A Baron YR 2019 UL http://gut.bmj.com/content/68/3/475.abstract AB Objective Serrated lesions such as sessile serrated adenomas or polyps (SSA/Ps) are important colorectal cancer precursors, but aetiological factors for these lesions are largely unknown. We aimed to determine the effects of calcium and vitamin D supplementation on the incidence of serrated polyps (SPs) in general and hyperplastic polyps and SSA/Ps specifically.Design Participants with one or more adenoma at baseline were randomised to receive 1200 mg/day of elemental calcium, 1000 IU/day of vitamin D3, both or neither agent. Treatment continued for 3 or 5 years, when risk of polyps was determined from surveillance colonoscopy (treatment phase). Outcomes after treatment ceased were also assessed (observational phase). Adjusted risk ratios (aRRs) of SPs were determined via multivariable generalised linear models.Results SPs were diagnosed in 565 of 2058 (27.5%) participants during the treatment phase and 329/1108 (29.7%) during the observational phase. In total, 211 SSA/Ps were identified during follow-up. In the treatment phase, there was no effect of either calcium or vitamin D on incidence of SSA/Ps. However, during the later observational phase, we observed elevated risks of SSA/Ps associated with calcium alone and calcium+vitamin D treatment (aRR (95% CI): 2.65 (1.43 to 4.91) and 3.81 (1.25 to 11.64), respectively).Conclusion In a large multicentre chemoprevention study, we found evidence that calcium and vitamin D supplementation increased the risk of SSA/Ps. This appeared to be a late effect: 6–10 years after supplementation began. These possible risks must be weighed against the benefits of calcium and vitamin D supplementation. Trial registration number NCT00153816; Results.