Effect of tea consumption on the risk of colon and rectal cancers

The current body of knowledge suggests that diet might influence colorectal carcinogenesis. Tea extracts and tea polyphenols may reduce risk of colon and rectal cancers through protection against DNA damage and induction of apoptosis. The meta-analysis of the published literature on the relationship of tea drinking and the risk of colon and rectal cancers in human populations found that a hospital-based design and low levels of tea consumption in the population might mask the suggested protective associations. The population-based case-control study on tea and rectal cancer in Moscow showed an inverse association. However, the strength of the association was greatly influenced by the methods of exposure assessment. The strongest protective association was observed when tea was measured as dry tea intake as opposed to volume of average beverage consumed or tea concentrate (zavarka). This finding implies that exposure misclassification might critically influence the results of epidemiological studies on this topic. The analysis of the North Carolina Colon Cancer Study might serve as an illustration of this implication. In this study, assessment of tea consumption did not take into account the strength of tea consumed. No association was found in men and women and increased colon cancer incidence was associated with reporting of ≥2 servings of tea per day in men. This positive association confined to a sub-group of subjects was attributed to the possible over-reporting of tea consumption in male cases due the disease status. The findings of this dissertation provide a basis for the further methodological improvement of the epidemiological studies of health effects associated with tea drinking.