Epidemiological studies have generally shown a decreased occurrence of cancer in those individuals who drink green tea regularly, although this has not been observed in all studies. A 2003 prospective cohort study using 13-year follow-up data found increased green tea consumption was associated with an apparent delay of cancer onset and death, and all cause deaths (Nakachi et al 2003). A phase 2 RCT evaluated the effects of green tea on oxidative DNA damage in 143 heavy smokers over 4 months and found a significant reduction in damage as evaluated from urine and plasma (Hakim et al 2003). A small, controlled, pilot study concluded with similar results when cells from the oral mucosa of smokers showed much less oxidative damage when compared with controls (Schwartz et al 2005). These trials indicate that green tea may be effective in reducing cancer in smokers, but much larger trials are needed. In contrast, a 2001 prospective study in Japan found no association between green tea consumption and cancer incidence (Nagano et al 2001).
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