Description of the Evidence
In a population-based prospective cohort study of 61,463 women in Sweden, individuals who consumed very low amounts of fruits and vegetables (<1.5 servings of fruit and vegetables/day) had a RR for developing CRC of 1.65 (95% CI, 1.23-2.2; P trend = .001) as compared with those individuals who consumed more than 2.5 servings. There was little evidence, however, of a benefit for higher as compared with moderate consumption (more than vs. fewer than 3.5 servings). Limitations of this study are that dietary intake during the study period was not reassessed over time, and the influence of physical activity could not be accurately determined. In addition, the conclusion about very low amounts of intake of fruits and vegetables is based on a retrospective subdivision of the lowest quartile of consumption, and its strength has not been adjusted for other potential confounding factors.
Six case-control studies and three cohort studies have explored potential dietary risk factors for colorectal adenomas.[20,100,114] Four of the nine found an association of fiber, carbohydrates, and/or vegetables with reduced risk. In one study, cases with moderate or severe dysplasia had a significantly lower intake of cruciferous vegetables than those with mild dysplasia. No significant effect of dietary fiber on colorectal adenoma was found in the large cohort study of U.S. nurses.
High-fiber cereal supplements during a 3-year period did not result in a decrease in adenoma recurrence in a RCT of 1,303 individuals. In a multicenter RCT, a diet low in fat (20% of total calories) and high in fiber (18 g of dietary fiber/1,000 kcal) and fruits and vegetables (3.5 servings per 1,000 kcal) was not associated with a reduction in the risk of recurrence of colorectal adenomas.
In a prospective cohort study of 35,215 Iowa women, an inverse association between the risk of colon cancer and vitamin E intake was found; the RR for the highest compared with the lowest quartile was 0.3 (95% CI, 0.19-0.54). The Women's Health Study, however, showed no relationship between CRC in women and the use of 600 IU of vitamin E every other day. In a meta-analysis of 14 randomized trials of supplemental antioxidant vitamins encompassing 170,025 individuals, no evidence of prevention of colorectal adenomas or cancer or other gastrointestinal tumors was found. A systematic review of published observational studies that provide sufficient data to calculate the dose-response relationship of serum 25-hydroxyvitamin D or oral intake of vitamin D with the risk of CRC was conducted. The results suggested that a daily intake of 1,000 IU of vitamin D-half the safe upper limit for intake established by the National Academy of Sciences-and a concentration of serum 25-hydroxyvitamin D of 33 ng/mL were each associated with a 50% lower risk of CRC. In a population-based case-control study, an inverse relationship between vitamin D intake and risk of CRC was found.