Green tea is made from the Camellia sinensis the Camellia sinensis leaves that have not undergone the same weathering and oxidation applied when processing Camellia sinensis into Oolong tea and black tea. Green tea originated in China, but its production has spread to many countries in Asia.
Several varieties of green tea exist, which differ substantially due to growing conditions, horticulture, production processing, and time of harvest.
There is no conclusive evidence that green tea helps to prevent or treat cancer in people. A review of existing studies concluded that while suggestive evidence existed, it did not amount to a clear indication of benefit.
Daily consumption of black tea (but not green tea) has been associated with a significant reduction in death from all cancers. There is limited evidence to suggest that green tea consumption may be associated with a slightly lower risk of esophageal cancer in the Chinese population, a lower risk of lung cancer in women, and a lower risk of oral cancer in Asian people. A 2015 meta-analysis of nine prospective cohort studies concluded that a high amount of green tea consumption may be associated with a lower risk of liver cancer in Asian women.This association was not seen in Asian men or when one cup of green tea was consumed daily. Similarly, another analysis of observational data conducted in 2012 suggested that green tea consumption may have a favorable effect on lung cancer risk. The observed effect was strongest in those who consumed more than seven cups of green tea daily. A 2011 meta-analysis of epidemiological studies found limited evidence that green tea consumption may be associated with a moderately reduced risk of liver cancer in Chinese and Japanese people.
Limited evidence suggests that green tea consumption is not associated with the risk of developing pancreatic cancer or prostate cancer.The link between green tea consumption and stomach cancer risk is unclear due to inconsistent evidence.
Green tea interferes with the chemotherapy drug bortezomib (Velcade) and other boronic acid-based proteasome inhibitors, and should be avoided by people taking these medications.