Introduction 1 2 1 2 3 4–21 in vitro 2 22–35 The aim of this review is to assess evidence from experimental and epidemiological studies whether green tea is a risk modifier for those exposed to tobacco smoke. The focus is on the measurement of green tea exposure undertaken in these studies. Methods Articles published since 1990 were located by searching electronic databases PubMed, Ovid and Science Direct, using keywords ‘lung cancer’, ‘tea’ and ‘smoking’ without any restriction on language. After relevant articles had been located, further papers were obtained from their reference lists. A total of 78 relevant articles were eventually found. Results and Discussion In vitro in vitro Period of exposure in vitro 32 in vitro a a a 22 23 29 33 34 23 33 34 Dose of exposure −1 −1 32 33 34 29 36 33 29 29 Human Trials Short-term effect 37 38 30 39 Protective effect from regular consumption 35 35 27 40 25 Lung tumor treatment 41 −2 Limitation of human trials 27 40 35 25 27 40 30 37 38 Mechanisms Based on Experimental Studies Fig. 1 36 36 Table 1 in vitro 2 8 28 31 42 27 11 22 35 36 35 11 33 in vitro 26 43 44 45 Epidemiological Studies Induction time and latent period of lung carcinoma 46 47 48 49 Measurement of green tea exposure and other limitations Table 2 50–52 50 51 53–55 54 55 53 53 In summary, there is only limited evidence from epidemiological studies that green tea is protective against lung cancer among smokers. Moreover, green tea exposure was generally taken to be within 5 years of interview or follow-up, which would have little impact on the incidence of lung cancer. Conclusion in vitro