Researchers from the Vanderbilt-Ingram Cancer Center surveyed women enrolled in the Shanghai Women's Health Study, a population-based study of approximately 75,000 middle-aged and older Chinese women.
During the 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.
The researchers found that regular tea consumption, defined as tea consumption at least three times a week for more than six months, was associated with a 17 per cent reduced risk of all digestive cancers combined.
A further reduction in risk was found to be 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 per cent reduced risk of digestive system cancers.
The trend toward fewer digestive cancers was strongest for stomach/esophageal and colorectal cancers.
"For all digestive system cancers combined, the risk was reduced by 27 per cent among women who had been drinking tea regularly for at least 20 years," lead author Sarah Nechuta said in a statement.
"For colorectal cancer, risk was reduced by 29 per cent among the long-term tea drinkers. These results suggest long-term cumulative exposure may be particularly important," Nechuta said.
Tea contains polyphenols or natural chemicals that include catechins like EGCG and ECG. Catechins have antioxidant properties and may inhibit cancer by reducing DNA damage and blocking tumour cell growth and invasion.
The researchers also asked about other lifestyle factors including the kinds of food eaten regularly, exercise habits, education level and occupation. Women who had ever smoked or who drank alcohol were excluded from the study.
Regular tea drinkers in the study were younger, had higher education, exercised more and consumed more fruits and vegetables. While the researchers adjusted for these factors, they could not rule out an effect from these and other unmeasured lifestyle habits.
The study was conducted in nonsmoking and nondrinking Chinese women to minimise the potential influence of these two risk factors on the results for tea consumption and digestive system cancer risk.
The study was published in the American Journal of Clinical Nutrition.
