"These findings extend related observations on the anticarcinogenic potential of tea ingredients and suggest that consumers may benefit more by drinking both green and black teas," wrote lead author Mendel Friedman in the Journal of the Agricultural and Food Chemistry. "Because tumor promotion may be the only reversible event during cancer development, its suppression is regarded as an effective way to inhibit carcinogenesis."
Green tea contains between 30 and 40 percent of water-extractable polyphenols, which previous studies have already linked to weight loss benefits, protection from Alzheimer's disease, and a decreased risk of certain cancers. Black tea -- green tea that has been oxidized through fermentation -- contains somewhere between 3 and 10 percent of polyphenols, and semi-fermented oolong tea's polyphenol content stands somewhere between green and black. Tealeaves contain four primary polyphenols: Epigallocatechin gallate (EGCG), epigallocatechin, epicatechin gallate, and epicatechin.
Friendman joined with researchers from the South Korean universities of Keimyung, Uiduk and Yeungnam to study the effects of nine green tea catechins, three black tea theaflavins, and theanine -- extracted using either water or a water/ethanol mix -- on human cancer cells and normal cells. The majority of the compounds, and all general tea extracts, reduced human breast, colon, liver and prostate cancer cells. The water/ethanol extracts were found to contain higher levels of flavonoids and kill more cancer cells, but the flavonoid levels of the teas did not correspond with the anticancer activities, the researchers said.
The results of the study merit further investigation, they added.
"Because it may be too risky to translate results from cell assays to in vivo effects, the observed destruction of a broad range of cancer cells suggests the need for animal and human studies designed to ascertain whether the observed wide variation in potencies of tea compounds and teas can predict corresponding effects in vivo," they wrote.
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