Abstract

Identification of dietary agents related to colorectal carcinogenesis is of high importance to decrease the global burden of this severe disorder. As flavonoids abundantly present in plant-based food items are suggested to exert various anticancer activities in numerous experimental models, evidence from epidemiological studies about association between dietary intake of these plant secondary metabolites and the risk of colorectal cancer was compiled and is discussed in this review article. Several case-control studies have demonstrated that dietary intake of selected subclasses of flavonoids and also some individual compounds can be inversely associated with colorectal cancer risk. However, these findings are not in complete agreement and are mostly not confirmed also by the results of prospective cohort studies. Several reasons are proposed to explain discrepancies and inconsistencies of findings obtained from different works, starting from the dependence of flavonoid content on cultivation conditions of plants and methods of food processing to the factors related to study design. At that, food sources of flavonoids (tea or non-tea flavonoids) can affect the role of these polyphenolic agents on development of colorectal cancer and the potential protective effects may also depend on cancer subsites, i.e. tumors in proximal vs. distal colon or rectum. Therefore, associations between flavonoids intake and colorectal malignancies are complex and biological mechanisms and physiological importance of various established and still unknown factors certainly need more investigation. Also, further large-scale prospective cohort studies in different populations are required before any public health recommendations can be formulated for general population or at-risk individuals.

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