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Extensive experimental and observational data suggest that intake of calcium and of vitamin D exert protective effects on colorectal neoplasia. Building on their previous work, the investigators will investigate the chemopreventive effect of vitamin D in the large bowel, to study whether calcium with vitamin D is more effective than calcium alone, and to confirm their positive finding regarding calcium. The goal of this study is the development of chemopreventive combinations that will reduce risk of colorectal neoplasia sufficiently to permit the lengthening of surveillance intervals in most patients and to clarify important issues regarding the mechanisms of colorectal carcinogenesis and chemoprevention.
This study is a double-blind, placebo-controlled trial of vitamin D and/or calcium supplementation for the prevention of large bowel adenomas. Subjects will be recruited from 10 Study Centers in North America. Eligible subjects will have had at least one large bowel adenoma removed in the 4 months prior to study entry and no remaining polyps in the bowel after complete colonoscopic examination. Participants will be randomized in a modified 2 x 2 factorial design to vitamin D (1000 IU/day), calcium carbonate (1200 mg elemental calcium/day), both agents, or placebo only. Women who decline to forego calcium supplementation will be randomized only to calcium alone or to calcium plus vitamin D. Randomization will be stratified by gender, study center of recruitment, and anticipated follow-up interval (see below), and will be conducted separately for female subjects randomized only to vitamin D. We anticipate enrolling about 2500 participants to reach a total of approximately 2000 randomized subjects. As safety measures, blood levels of calcium, creatinine, and 25-(OH)-vitamin D will be obtained at baseline and 1 year after randomization, as well as 3 years after randomization for subjects with a 5-year surveillance cycle. Every six months after randomization subjects will complete a questionnaire regarding compliance with study agents, use of medications and vitamin/mineral supplements, illnesses, hospitalizations, and dietary intake of calcium and vitamin D. The endpoint of the study will be new adenomas detected on follow-up colonoscopy. These examinations are scheduled to occur either 3 years or 5 years after the qualifying examination, depending on the follow-up interval recommended by each patient's endoscopist. Some patients may, for medical reasons, have a colonoscopy at a time other than 3 or 5 years after the qualifying examination. Information from these exams will be included in analyses where appropriate. In the primary analyses, the occurrence of new neoplastic polyps in the interval between randomization and the follow-up exam will be compared between subjects randomized to vitamin D (with or without calcium) versus those randomized to placebo (with or without calcium), between subjects randomized to calcium (with or without vitamin D) versus those randomized to placebo (with or without vitamin D, excluding women electing to receive calcium and therefore cannot participate in the calcium component of the study), and between those randomized to calcium plus vitamin D versus those randomized to calcium alone. In secondary analyses, we will examine the effect of calcium plus vitamin D versus vitamin D alone, and the impact of baseline vitamin D levels and VDR polymorphisms on the vitamin D effects. Effects on advanced adenomas will also be assessed.
Allocation: Randomized, Control: Placebo Control, Endpoint Classification: Efficacy Study, Intervention Model: Factorial Assignment, Masking: Double Blind (Subject, Caregiver, Investigator, Outcomes Assessor), Primary Purpose: Prevention
Calcium Carbonate, Vitamin D3, placebo
University of Southern California
Active, not recruiting
Dartmouth-Hitchcock Medical Center
Published on BioPortfolio: 2014-08-27T03:51:34-0400
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