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© The Author 2007. Published by Oxford University Press.
ARTICLE |
Prolonged Effect of Calcium Supplementation on Risk of Colorectal Adenomas in a Randomized Trial
Affiliations of authors: Department of Community and Family Medicine (MVG, KW, ELB, BFC), Departments of Medicine and Community and Family Medicine (JAB, RR), Dartmouth Medical School, Lebanon, NH; Department of Medicine, University of North Carolina School of Medicine, Chapel Hill, NC (RSS); Department of Preventive Medicine, University of Southern California School of Medicine, Los Angeles, CA (RWH); Division of Occupational and Environmental Health, School of Public Health, University of Minnesota, Minneapolis, MN (TRC); Department of Biostatistics and Epidemiology, Cleveland Clinic Foundation, Cleveland, OH (GJB); Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, IA (RWS); Department of Pathology, Fairview Southdale Hospital, Minneapolis, MN (DCS); Rollins School of Public Health, Emory University, Atlanta, GA (JSM)
Correspondence to: John A. Baron, MD, 46 Centerra Driveway, Ste. 300, Lebanon, NH 03766 (e-mail: John.A.Baron{at}dartmouth.edu).
BACKGROUND: Calcium supplementation has been shown to decrease the risk of recurrence of colorectal adenomas in randomized trials. However, the duration of this protective effect after cessation of active supplementation is not known.
METHODS: In the Calcium Polyp Prevention Study, 930 subjects with a previous colorectal adenoma were randomly assigned from November 1988 through April 1992 to receive placebo or 1200 mg of elemental calcium daily for 4 years. The Calcium Follow-up Study was an observational phase of the trial that tracked adenoma occurrence for an average of 7 years after the end of randomized treatment and gathered information regarding the use of medications, vitamins, and supplements during that time. We obtained follow-up information for 822 subjects, 597 of whom underwent at least one colonoscopy after the end of study treatment and are included in this analysis. Generalized linear models were used to compute relative risks (RRs) and 95% confidence intervals (CIs) for the effect of randomized calcium treatment on risk of adenoma recurrence during the first 5 years after study treatment ended and during the subsequent 5 years. Statistical tests were two-sided.
RESULTS: During the first 5 years after randomized treatment ended, subjects in the calcium group still had a substantially and statistically significantly lower risk of any adenoma than those in the placebo group (31.5% versus 43.2%; adjusted RR = 0.63, 95% CI = 0.46 to 0.87, P = .005) and a smaller and not statistically significant reduction in risk of advanced adenomas (adjusted RR = 0.85, 95% CI = 0.43 to 1.69, P = .65). However, the randomized treatment was not associated with the risk of any type of polyp during the next 5 years. The findings were broadly similar when the analysis was restricted to subjects who did not report use of any calcium supplements after the treatment phase of the trial ended.
CONCLUSION: The protective effect of calcium supplementation on risk of colorectal adenoma recurrence extends up to 5 years after cessation of active treatment, even in the absence of continued supplementation.
| CONTEXT AND CAVEATS Prior knowledge In randomized trials, calcium supplementation has been found to reduce the risk of colorectal adenomas in individuals with a previous adenoma. However, the duration of the protective effect was not determined. Study design Participants in a randomized trial of calcium supplementation for colorectal adenoma prevention were followed for an average of 7 years after the end of randomized treatment. Contribution During the first 5 years after randomized treatment ended, subjects in the calcium group continued to have a lower risk of adenomas (31.5%) than those in the placebo group (43.2%). However, after 5 years, no difference between groups was evident. The result was similar when the analysis was restricted to subjects who did not take calcium supplements. Implications The protective effect of calcium treatment on colorectal adenomas in persons at high risk of these tumors extends for up to 5 years beyond active treatment. Limitations Data from follow-up colonoscopies were not available for all subjects, and the interval between the end of treatment and the follow-up colonoscopy varied. Information on dietary calcium intake during the follow-up period was not available.
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Editorial about this Article
- Calcium Supplementation and Prevention of Colorectal Neoplasia: Lessons From Clinical Trials
- María Elena Martínez and Elizabeth T. Jacobs
J Natl Cancer Inst 2007 99: 99-100.[Extract] [Full Text] [PDF]
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