Drinking plenty of tea can lower your risk of developing type 2 diabetes, according to a study of more than a million adults. Four or more cups of black, green or oolong tea each day is associated with a 17% lower risk of developing type 2 diabetes. Moderate consumption of black, green or oolong tea is associated with a lower risk of type 2 diabetes (T2D), according to the results of a systematic review and meta-analysis of 19 cohort studies involving more than 1 million adults from eight countries. . The findings suggest that drinking at least four cups of tea a day is associated with a 17% lower risk of T2D over an average period of 10 years. The study will be presented at this year’s European Association for the Study of Diabetes (EASD) annual meeting in Stockholm, Sweden (September 19-23). “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 from the University of Science and Technology in Wuhan in China. Tea contains various antioxidant, anti-inflammatory and anti-carcinogenic tea compounds. While it has long been known that regular tea consumption may be beneficial to health due to these properties, the relationship between tea consumption and T2D risk has been less clear. Published cohort studies and meta-analyses so far have reported inconsistent findings. To address this uncertainty, the researchers conducted a cohort study and a dose-response meta-analysis to better define the relationship between tea consumption and future T2D risk. Compared to adults who did not drink tea, those who drank 1-3 cups each day reduced their risk of developing T2D by 4%. Most impressively, those who consumed at least 4 cups a day reduced their risk by 17%. Initially, they studied 5,199 adults (2583 men, 2616 women) with a mean age of 42 years and no history of T2D from the China Health and Nutrition Survey (CHNS), who were recruited in 1997 and followed up until 2009. The CHNS is a multicenter prospective study that examines the economics, sociological issues and health of residents from nine provinces. At baseline, participants completed a food and beverage frequency questionnaire. They also provided information on lifestyle factors such as regular exercise, smoking and alcohol consumption. Overall, 2,379 (46%) participants reported drinking tea. By the end of the study, 522 (10%) participants had developed T2D. The researchers found that tea drinkers had a similar risk of developing T2D compared to non-drinkers after adjusting for factors known to be associated with an increased risk of T2D, such as age, gender and physical inactivity. Furthermore, 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 scientists conducted a systematic review of all cohort studies that investigated tea consumption and T2D risk in adults (aged 18 years and older) up to September 2021. In total, 19 cohort studies involving 1,076 participants. 311 participants from eight countries (China, USA, Finland, Japan, UK, Singapore, Netherlands and France) were included in the dose-response meta-analysis. They investigated the potential impact on T2D risk 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 (men and women) and the location of the study (Europe and America or Asia). Overall, the meta-analysis found a linear relationship between tea consumption and T2D risk, with each cup of tea consumed per day reducing the risk of T2D by approximately 1%. Compared to adults who did not drink tea, those who drank 1-3 cups daily reduced their risk of T2D by 4%. Most impressively, those who consumed at least 4 cups each day reduced their risk by 17%. The associations held regardless of the type of tea the participants drank, whether they were male or female, or where they lived. This suggests that it may be the amount of tea consumed, rather than any other factor, that plays an important role. “While more research is needed to determine the exact dose and mechanisms behind these observations, our findings suggest that tea consumption is beneficial in reducing the risk of type 2 diabetes, but only at high doses (at least 4 cups the day)”. , says Lee. He adds, “It’s possible that specific components of tea, such as polyphenols, lower blood glucose levels, but it may take a sufficient amount of these bioactive compounds to be effective. It may also explain why we did not find an 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 made from the same plant used to make green and black tea. The difference is how the tea is processed – green tea is not allowed to oxidize much, black tea is allowed to oxidize until it turns black, and oolong tea is partially oxidized. Despite the important findings, the authors note that the study is observational. Therefore, it cannot prove that tea consumption is the cause of the reduced risk of T2D, although it suggests that it is a possible factor. In addition, the research team points out several caveats, including that it was based on subjective estimates of the amounts of tea consumed and cannot rule out the possibility that residual confounding from other lifestyle and physiological factors may have affected the results. The study was funded by the Young Talents Project of Hubei Provincial Health Commission, China. Science and Technology Research Core project of the Ministry of Education of Hubei Province, China. Sanuo Diabetes Charity Foundation, China; and Xiangyang Science and Technology Plan Project, China.
