According to a systematic review and meta-analysis of 19 cohort studies involving over one million adults from eight countries, moderate to high consumption of black, green, or Oolong tea is associated with a lower risk of developing type 2 diabetes (T2D). The experts – led by the Wuhan University of Science and Technology in China – have found that drinking at least four cups of tea per day was linked to a 17 percent lower risk of developing T2D over an average period of ten years.
“Our results are exciting because they suggest that people can do something as simple as drinking four cups of tea a day to potentially lessen their risk of developing type 2 diabetes,” said study lead author Xiaying Li, a researcher at Wuhan University.
Although scientists have long known that regular tea consumption has many health benefits due to tea’s various antioxidant, anti-inflammatory, and anticarcinogenic compounds, until now the relationship between drinking tea and the risk of diabetes has not been investigated systematically.
In an initial phase, the Wuhan researchers studied 5,199 adults (2583 men and 2616 women with an average age of 42) with no history of T2D from the China Health and Nutrition Survey (CHNS – a multicenter prospective study investigating the economics, sociological issues, and health of Chinese residents) who were recruited in 1997 and followed until 2009.
The participants had to fill in a drink and food frequency questionnaire and provide information about lifestyle factors including exercise, smoking, and alcohol consumption. Overall, 2,379 (46 percent) of the participants reported drinking tea, and by the end of the study, 522 (10 percent) of them had developed T2D. However, after adjusting for factors such as age, sex, and physical activity, the scientists found that tea drinkers had a similar risk of developing T2D as non-drinkers.
In a second step, the researchers performed a systematic review of all cohort studies investigating the correlation between tea drinking and T2D risk in 1,076,311 adults from eight countries, and explored the potential impact of different types of tea (green, black, and oolong), the amount of tea consumed (less than one cup per day, one to three cups, and four or more cups), sex, and location on the risk of developing T2D.
The analysis revealed that each cup of tea consumed per day reduced the risk of T2D by one percent. However, those who drank at least four cups each day reduced their risk by 17 percent, regardless of the type of tea they consumed. “While more research needs to be done to determine the exact dosage and mechanisms behind these observations, our findings suggest that drinking tea is beneficial in reducing the risk of type 2 diabetes, but only at high doses (at least four cups a day),” Li explained.
“It is possible that particular components in tea, such as polyphenols, may reduce blood glucose levels, but a sufficient amount of these bioactive compounds may be needed to be effective. It may also explain why we did not find an association between tea drinking and type 2 diabetes in our cohort study, because we did not look at higher tea consumption,” she concluded.
The study will be presented at the European Association for the Study of Diabetes (EASD) Annual Meeting in Stockholm, Sweden (19-23 September, 2022).