As a result of many studies in descriptive and analytic epidemiology, in animal carcinogenesis, and in the direct examination of body fluids for mutagens/carcinogens, it is possible to develop a list of dietary factors that may be associated with the high rate of colon cancer and related cancers in Western countries. This paper is concerned with the design of intervention studies to clarify which of these factors is important. The size of such intervention trials is influenced primarily by two factors: the incidence of the disease outcome studied in a control population and the magnitude of risk reduction in a treated group. Calculations based on a variety of assumptions suggest that a randomized trial in which cancer mortality is measured as the outcome of the intervention in a healthy population is probably too costly to be justified by current evidence linking the disease to diet. However, precursor lesions can be considered as an alternative outcome. The choice of the precursor lesion depends on the link to the disease in question, the prevalence of the lesion in the population, and the ease of detection. Recent developments in the application of endoscopic methods and in the description of the pathologic process leading to cancer suggest the use of gastrointestinal polyps as "precursor lesions" as the outcome of a trial. We illustrate these points with a protocol for a study in progress, a randomized double-blind study of the effect of ascorbic acid and alpha-Tocopherol on the rate of recurrence of colorectal polyps.

Background: While the association between bioavailability of vitamins E and C and Helicobacter pylori infection has been extensively researched in gastritis and gastric cancer patients, little is known about this relationship in asymptomatic adults. Aim: To investigate the effect of H. pylori infection on bioavailability of vitamins E and C in asymptomatic adults. Methods: Volunteers from the University of Toronto, aged 18–45 years, were screened, for their H. pylori infection status. H. pylori-negative (n = 32) and asymptomatic H. pylori-positive (n = 27) participants received vitamin C (500 mg) and vitamin E (400 IU) supplements daily for 28 days. Plasma vitamins C, E and thiols concentrations were assessed before (baseline) and after supplementation. Results: Postsupplementation plasma levels of vitamin C and E were significantly higher than presupplementation levels in both groups. Yet, changes in plasma vitamins E and C were not significantly different between the two groups [vitamin C (µmol/l): 13.97 ± 16.86 vs. 20.87 ± 27.66, p > 0.05; vitamin E (µmol/l): 15.52 ± 9.4 vs. 14.47 ± 15.77; p > 0.05 for H. pylori-negative and H. pylori-positive groups, respectively]. In addition, no significant difference was found in plasma thiols levels between groups (p > 0.05). Conclusion: These findings suggest that H. pylori does not influence antioxidants bioavailability in its asymptomatic stages of infection until a factor or combination of factors triggers the inflammation cascade which may lead to increased oxidative stress and possibly reduced bioavailability of vitamins E and C.

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