The study – published in the American Journal of Clinical Nutrition- investigated the association between regular tea consumption and the incidence of digestive system cancers, finding that women who drank green tea for prolonged periods of time had a lower incidence of developing certain digestive system cancers, especially cancers of the stomach, esophagus and colorectum.
Led by Dr Sarah Nechuta from Vanderbilt University Medical Center, USA, the researchers determined the impact of green tea consumption on the risk of cancer in approximately 75,000 middle-aged and older Chinese.
"For all digestive system cancers combined, the risk was reduced by 27% among women who had been drinking tea regularly for at least 20 years," said Nechuta, who added that the specific for colorectal cancer risk was reduced by 29% among the long-term tea drinkers.
“These results suggest long-term cumulative exposure may be particularly important," she said.
The study adds to the list of potential health benefits of green tea and the compounds it contains.
The majority of science on tea has looked at green tea, with benefits reported for reducing the risk of Alzheimer's and certain cancers, improving cardiovascular and oral health, and helping with weight management.
Green tea contains between 30 and 40% of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3% and 10%. Oolong tea is semi-fermented tea and is somewhere between green and black tea.
The four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC).
Nechuta and her team investigated the association of regular tea intake – defined as more than three times per week for more than six months – with the risk of digestive system cancers using data from the Shanghai Women's Health Study.
During an initial interview participants were asked if they drank tea, the type of tea consumed and how much they consumed. Most of the Chinese women reported drinking primarily green tea, they said. Women in the study were then followed for an average of 11 years, in which time 1255 digestive system cancers occurred.
Nechuta and her team found that regular tea consumption was associated with a 17% reduced risk of all digestive cancers combined.
Further reductions in risk were associated with an increased level of tea drinking. Specifically, those who consumed about two to three cups per day (at least 150 grams of tea per month) had a 21% reduced risk of digestive system cancers.
“In comparison with women who never drank tea, regular tea intake (mostly green tea) was associated with reduced risk of all digestive system cancers combined, and the reduction in risk increased as the amount and years of tea consumption increased,” reveal the researchers.
Source: American Journal of Clinical Nutrition
Published online ahead of print, doi: 10.3945/ajcn.111.031419
“Prospective cohort study of tea consumption and risk of digestive system cancers: results from the Shanghai Women's Health Study”
Authors: Sarah Nechuta, Xiao-Ou Shu, Hong-Lan Li, Gong Yang, et al