[Colorectal cancer and folate]

Nutritional factors are important contributors to colorectal cancer prevention. There is some evidence to suggest that a high dietary folate intake is associated with a reduced risk of colorectal cancer. Folate, which is found in green leafy vegetables, is involved in C1 group transfer and contributes to purin and thymi-dilate synthesis as well as to DNA methylation. Alterations in gene expression and DNA damage are discussed to result from low folate levels and might be associated with an elevated risk of colorectal malignancies. This hypothesis can be supported by the finding that a common polymorphism in the methylentetrahydrofolate reductase gene enhances the risk of colorectal cancer when folate status is low. Both retrospective and prospective epidemiologic studies confirm the observation that a high intake of folate correlates with a lower risk of colorectal cancer. There is also evidence from epidemiological studies that diets which are low in methyl donors, such as low contents of folate and/or methionine combined with relatively high alcohol consumption, even enhance the risk of colorectal cancer. A small number of intervention trials provide first evidence that folate intakes far above recommended dietary allowances might influence possible biomarkers of colorectal tumours.