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
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