Dietary iron and cancer of the rectum: a case-control study in Uruguay

In order to examine the relationship between dietary iron intake and risk of rectal cancer, a case-control study was carried out in Montevideo, Uruguay. In the time period 1994-1998, 216 newly diagnosed and microscopically verified cases of adenocarcinoma and 433 controls hospitalized for diseases not related with long-term changes in diet were enrolled in the study. Controls were frequency matched to cases on age, sex, residence and urban/rural status. Both series of patients were interviewed face-to-face in the four major hospitals in Montevideo by two trained social workers. Dietary iron was associated with significant increases in risk in men, women, and in both sexes together [odds ratio (OR) 3.2, 95% confidence interval (CI) 1.9-5.3 for the highest tertile of consumption versus the lowest one]. Since meat and its major macronutrients were potential confounders, iron intake was adjusted for these variables without major changes in the results. Furthermore, dietary iron and total fat combined its effects according to a multiplicative model (OR 3.3, 95% CI 1.8-5.8). Finally, an interaction between dietary iron and vitamin C was found. According to the results, iron displayed a significant increase in risk at low levels of vitamin C intake (OR 4.9, 95% CI 2.3-10.5). These results, together with the existing epidemiological and experimental evidence, suggest that dietary iron could play an important role in rectal carcinogenesis.