Tea and its constituents have shown antioxidative, anti-inflammatory, and anticarcinogenic activities in numerous in vitro and animal studies (1, 2). Organ sites that are accessible directly to orally administered tea, such as digestive tract, are thought to represent good targets for potential chemoprevention by tea because of the high bioavailability (2). A number of epidemiologic studies, mostly with case-control study design, have evaluated this hypothesis in various populations and yielded inconsistent results (3, 4). Differences in tea-drinking habits, types of tea consumed, and consumption levels may have contributed to some of the inconsistency (3, 5). Failure to control for potential confounding factors and inadequate assessment of tea consumption may also be important contributors (3).
Tea is the most popular beverage consumed in China. We have previously reported inverse associations between green tea consumption and risks of certain digestive tract cancers (6-9), including colorectal cancer (CRC), in case-control studies conducted in urban Shanghai. In this report, we analyzed the data from a large prospective cohort study in urban Shanghai with detailed and repeated assessment of tea consumption to test the hypothesis that green tea consumption may reduce the risk of CRC.