Summary: Drinking four or more cups of black, green or oolong tea per day was associated with a 17% lower risk of developing type 2 diabetes.
A systematic review and meta-analysis of 19 cohort studies involving more than 1 million adults from eight countries finds that moderate consumption of black, green or oolong tea is linked to a lower risk of developing type 2 diabetes.
The findings, presented at the annual meeting of the European Association for the Study of Diabetes (EASD) in Stockholm, Sweden (September 19-23), suggest that drinking at least four cups of tea a day s ‘associated with a 17% lower risk. of T2D over an average period of 10 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 reduce their risk of developing type 2 diabetes,” says lead author Xiaying Li of the University of Science and Technology from Wuhan in China.
Although it has long been known that drinking tea regularly can be beneficial to health due to the various antioxidant, anti-inflammatory and anti-cancer compounds contained in tea, the relationship between tea consumption and the risk of T2D is less clear. To date, published cohort studies and meta-analyses have reported inconsistent findings.
To address this uncertainty, researchers conducted a cohort study and dose-response meta-analysis to better define the relationship between tea consumption and future risk of T2DM.
First, they studied 5,199 adults (2,583 men, 2,616 women) without a history of T2D (mean age 42 years) from the China Health and Nutrition Survey (CHNS), who were recruited in 1997 and followed until 2009. The CHNS is a multicenter perspective. study of the economy, sociological problems and health of the residents of nine provinces.
At baseline, participants completed a food and beverage frequency questionnaire and provided information on lifestyle factors such as regular exercise, smoking, and alcohol consumption. In total, 2,379 (46%) participants reported drinking tea, and by the end of the study, 522 (10%) participants had developed T2D.
After adjusting for factors known to be linked to an increased risk of T2D, such as age, sex and physical inactivity, the researchers found that tea drinkers had a similar risk of developing T2D compared to non-drinkers. And the results did not change significantly when analyzed by age and sex, or when participants who developed diabetes during the first 3 years of follow-up were excluded.
In the next step of the study, the researchers conducted a systematic review of all cohort studies investigating tea consumption and T2D risk in adults (aged 18 years and older) up to September 2021. In total , 19 cohort studies included 1,076,311 participants from eight countries.  were included in the dose-response meta-analysis.
They explored the potential impact of different types of tea (green tea, oolong tea and black tea), frequency of tea consumption (less than 1 cup/day, 1-3 cups/day and 4 or more cups/day ). gender (male and female) and study location (Europe and America, or Asia), on the risk of T2D.
Overall, the meta-analysis found a linear association between tea consumption and T2D risk, with each cup of tea consumed per day reducing the risk of developing T2D by about 1%.
Compared to adults who did not drink tea, those who drank 1-3 cups daily reduced their risk of T2D by 4%, while those who consumed at least 4 cups each day reduced their risk by 17% .
The associations were seen regardless of the type of tea the participants drank, whether they were male or female, or where they lived, suggesting that it may be the amount of tea consumed, rather than any other factor, that plays an important role .
“Although more research is needed to determine the dosage and exact mechanisms behind these observations, our results suggest that drinking tea is beneficial in reducing the risk of type 2 diabetes, but only at high doses (at least 4 cups per day)”. , says Li.
He adds: “It is possible that certain components of tea, such as polyphenols, can lower blood glucose levels, but it may take sufficient amounts of these bioactive compounds to be effective. It may also explain why we did not find a association between tea consumption and type 2 diabetes in our cohort study, because we did not look at higher tea consumption.”
Oolong tea is a traditional Chinese tea that is made from the same plant used to make green and black teas. The difference is how the tea is processed: green tea is not oxidized much, black tea is oxidized until it turns black, and oolong tea is partially oxidized.
Despite the important findings, the authors note that the study is observational and cannot prove that drinking tea reduces the risk of T2D, but suggests that it is likely to contribute.
And the researchers note several caveats, including that they were based on subjective assessments of the amounts of tea consumed and cannot rule out the possibility that residual confounding by other physiological and lifestyle factors may have affected the results.
About this diabetes research news
Author: Judy Naylor
Contact: Judy Naylor – Diabetology
Image: The image is in the public domain
Original research: The results will be presented at the annual meeting of the European Association for the Study of Diabetes
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