Context: Knowledge of risk factors for colorectal neoplasia could inform risk reduction strategies for asymptomatic individuals. Few studies have evaluated risk factors for advanced colorectal neoplasia in asymptomatic individuals, compared risk factors between persons with and without polyps, or included most purported risk factors in a multivariate analysis. Objective: To determine risk factors associated with advanced colorectal neoplasia in a cohort of asymptomatic persons with complete colonoscopy. Design, Setting, and Participants: Prospective, cross-sectional study of 3121 asymptomatic patients aged 50 to 75 years from 13 Veterans Affairs medical centers conducted between February 1994 and January 1997. All participants had complete colonoscopy to determine the prevalence of advanced neoplasia, defined as an adenoma that was 10 mm or more in diameter, a villous adenoma, an adenoma with high-grade dysplasia, or invasive cancer. Variables examined included history of first-degree relative with colorectal cancer, prior cholecystectomy, serum cholesterol level, physical activity, smoking, alcohol use, and dietary factors. Main Outcome Measures: An age-adjusted analysis was performed for each variable to calculate the odds ratios (ORs) and 95% confidence intervals (CIs) associated with having advanced neoplasia compared with having no polyps. We developed a multivariate logistic regression model to identify the most informative risk factors. A secondary analysis examined risk factors for having hyperplastic polyps compared with having no polyps and compared with having advanced neoplasia. Results: Three hundred twenty-nine participants had advanced neoplasia and 1441 had no polyps. In multivariate analyses, we found positive associations for history of a first-degree relative with colorectal cancer (OR, 1.66; 95% CI, 1.16-2.35), current smoking (OR, 1.85; 95% CI, 1.33-2.58), and current moderate to heavy alcohol use (OR, 1.02; 95% CI, 1.01-1.03). Inverse associations were found for cereal fiber intake (OR, 0.95; 95% CI, 0.91-0.99), vitamin D intake (OR, 0.94; 95% CI, 0.90-0.99), and use of nonsteroidal anti-inflammatory drugs (NSAIDs) (OR, 0.66; 95% CI, 0.48-0.91). In the univariate analysis, the inverse association was found with cereal fiber intake greater than 4.2 g/d, vitamin D intake greater than 645 IU/d, and daily use of NSAIDs. Marginal factors included physical activity, daily multivitamin use, and intake of calcium and fat derived from red meat. No association was found for body mass index, prior cholecystectomy, or serum cholesterol level. Three hundred ninety-one patients had hyperplastic polyps as the worst lesion found at colonoscopy. Risk variables were similar to those for patients with no polyps, except that past and current smoking were associated with an increased risk of hyperplastic polyps. Conclusions: Our data endorse several important risk factors for advanced colonic neoplasia, and provide a rationale for prudent risk reduction strategies. Further study is needed to determine if lifestyle changes can moderate the risk of colorectal cancer.
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