Drinking plenty of tea may reduce your risk of developing type 2 diabetes, according to a study of more than one million adults.
Four or more cups of black, green, or oolong tea per day is linked to a 17% lower risk of developing type 2 diabetes.
Moderate consumption of black, green or oolong tea is linked to a lower risk of developing type 2 diabetes (T2D), according to 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 per day is associated with a 17% lower risk of T2D over an average 10-year period. The study will be presented at the annual meeting of the European Association for the Study of Diabetes (EASD) 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,” said lead author Xiaying Li of the Wuhan University of Science and Technology. in China.
Tea contains several antioxidant, anti-inflammatory and anti-carcinogenic compounds in tea. While it has long been known that drinking tea regularly for its properties can be beneficial to health, the relationship between drinking tea and the risk of T2D is less clear. Published cohort studies and meta-analyses to date have reported inconsistent findings.
To address this uncertainty, researchers conducted a cohort study and a dose-response meta-analysis to better define the relationship between tea consumption and future risk of T2D.
First, they studied 5,199 adults (2583 males, 2616 females) 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 until 2009. The CHNS is a multicenter prospective study on the economy, sociological problems and health of residents of nine provinces.
In the beginning, the participants completed a questionnaire about the frequency of eating and drinking. They also provided information on lifestyle factors such as regular exercise, smoking and alcohol consumption. A total of 2,379 (46%) participants reported drinking tea. At the end of the study, 522 (10%) participants had developed T2D.
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. In addition, the results did not change significantly when analyzed for age and gender, or when participants who developed diabetes during the first 3 years were excluded from follow-up.
In the next step of the study, the scientists systematically reviewed all cohort studies on tea drinking and the risk of T2D in adults (aged 18 or older) up to September 2021. A total of 19 cohort studies involving 1,076,311 participants from eight countries (China, USA, Finland, Japan, UK, Singapore, Netherlands and France) were included in the dose-response meta-analysis.
They examined the possible impact on the risk of T2D of different types of tea (green tea, oolong tea and black tea), the frequency of drinking tea (less than 1 cup/day, 1-3 cups/day and 4 or more cups/day), gender (male and female), and the location of the study (Europe and America, or Asia).
Overall, the meta-analysis found a linear association between tea drinking and T2D risk, with each cup of tea consumed per day reducing the risk of developing T2D by about 1%.
Compared to adults who didn’t drink tea, those who drank 1-3 cups daily lowered their risk of T2D by 4%. Even more impressive, those who drank at least 4 cups each day reduced their risk by 17%.
The associations persisted 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 a major role.
“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 for reducing the risk of type 2 diabetes, but only at high doses (at least 4 cups per day),” says Li.
She adds: “It is possible that certain components in tea, such as polyphenols, may lower 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 any association in our cohort study.” between tea drinking and type 2 diabetes, 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 teas. 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 drinking tea is the cause of the reduced risk of T2D, although it does suggest that it is a likely contributor.
In addition, the research team points out several caveats, including that they relied on subjective assessments of the amounts of tea consumed and cannot rule out the possibility that residual confusion from other lifestyle and physiological factors may have influenced the results.
The study was funded by the Young Talents Project of the Hubei Provincial Health Commission, China; Science and Technology Research Key Project of the Education Department of Hubei Province, China; Sanuo Diabetes Charity Foundation, China; and Xiangyang Science and Technology Plan Project, China.