Tea intake and liver diseases
Authors: Liang Shen
Journal: Hepatology (2010)

The possible beneficial effects of coffee and tea consumption on various diseases have attracted much attention in recent years. With great interest, I read the article by Freedman et al.,1 who demonstrated that regular coffee consumption was associated with lower rates of liver disease progression in a large prospective study of participants with advanced hepatitis C–related liver disease. However, the study found that tea consumption was not associated with reduced liver disease progression. Interestingly, a recent population-based, prospective cohort study by Ui et al.2 demonstrated a significant association between green tea consumption and a decreased risk of liver cancer. On the basis of its chemical constituents, tea (especially green tea) should have many benefits for patients with liver diseases. Besides its high caffeine content, green tea is usually rich in numerous polyphenols, which are strong antioxidants able to prevent oxidative stress in the pathogenesis of chronic liver diseases. Epigallocatechin gallate, an important chemopreventive agent in green tea, can inhibit the growth of many hepatocellular carcinoma cell lines.3, 4 Moreover, long-term treatment with epigallocatechin gallate has been proven to attenuate the development of fatty liver diseases.5 However, why was no association between tea intake and liver disease progression observed by Freedman et al.1? Here I offer some possible reasons for this interesting question. First, Ui et al.2 found that the inverse association between green tea consumption and the risk of liver cancer appeared to be a threshold effect rather than a dose-response relationship. The participants consuming five cups or more of green tea daily exhibited a significantly lower liver cancer risk. It is worth mentioning that Ui et al. conducted the prospective cohort study in Japan, which has the highest rate of consumption of green tea in the world. In comparison, only a small portion of the participants in the study by Freedman et al. had two or more cups of tea per day. Even though the contents of the bioactive compounds in tea may fluctuate because of differences in materials and manufacturing, it is still rational to postulate that the participants' levels of tea intake, much lower than the threshold level, may have been the principal reason that no favorable effect of tea was observed by Freedman et al. Moreover, because black tea and green tea differ markedly in the nature of their polyphenols,6 their preventive effects on liver diseases are expected to be different. Thus, it would be more reasonable to assess the favorable effects of black tea and green tea separately; otherwise, their respective outcomes may be confounded. I do not intend to judge whether tea intake has favorable effects on chronic liver diseases or not; I only want to offer some possible factors responsible for the distinct results of the two studies. Because tea is the most widely consumed beverage in the world, future studies designed to comprehensively elucidate the association of tea intake and liver diseases are encouraged. Liang Shen Ph.D.*, * Shandong Provincial Research Center for Bioinformatic Engineering and Technique, Shandong University of Technology, Zibo, People's Republic of China.