Moderate use of black, green, or oolong tea is associated with a lower risk of acquiring type 2 diabetes, according to a systematic review and meta-analysis of 19 cohort studies involving more than 1 million adults from eight different countries.
The research indicates that having at least four cups of tea per day is linked to a 17% lower risk of type 2 diabetes (T2D) over an average of ten years, according to findings presented at this year's European Association for the Study of Diabetes (EASD) Annual Meeting in Stockholm, Sweden (19-23 September). According to main author Xiaying Li of Wuhan University of Science and Technology in China, "our results are intriguing because they imply that people can do something as easy as drinking four cups of tea a day to potentially lower their chance of acquiring type 2 diabetes."
Because of the numerous antioxidant, anti-inflammatory, and anticarcinogenic components that tea contains, it has long been known that drinking tea frequently may be healthy, but the link between tea consumption and the risk of T2D has been less obvious. Cohort studies and meta-analyses that have been published so far have presented conflicting results.
To clarify the connection between tea drinking and future T2DM risk, researchers carried out a cohort study and a dose-response meta-analysis.
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First, they looked at 5,199 participants (2583 men and 2616 women; average age, 42) from the China Health and Nutrition Survey (CHNS), who were enrolled in 1997 and followed up within 2009 and had no prior history of T2D. The CHNS is a multicenter prospective study that examines inhabitants from nine provinces' socioeconomic conditions as well as their physical and mental health.
Participants initially completed a food and drink frequency questionnaire and supplied details on lifestyle choices such regular exercise, smoking, and alcohol use. 2,379 (46%) participants reported drinking tea overall, and 522 (10%) persons had T2D by the conclusion of the trial.
Researchers discovered that tea drinkers and non-drinkers had comparable risks of getting type 2 diabetes (T2D) after correcting for variables such as age, sex, and physical inactivity that are known to be associated with higher risk of T2D. And when patients who got diabetes during the first three years of follow-up were omitted or the results were broken down by age and sex, they did not significantly alter the findings.
The researchers then conducted a systematic evaluation of all cohort studies examining the relationship between tea consumption and the risk of T2D in adults (aged 18 or older) up until September 2021. The dose-response meta-analysis comprised 19 cohort studies totalling 1,076,311 participants from eight different nations.
They investigated the potential effects of various tea consumption patterns (less than one cup per day, one to three cups per day, and four or more cups per day), gender (male and female), and research region (Europe and America, or Asia), on the risk of T2D.
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Overall, the meta-analysis discovered a linear relationship between tea consumption and T2D risk, with each daily cup of tea lowering risk by about 1%.
Adults who drank 1-3 cups of tea per day had a 4% lower risk of T2D than those who didn't, while those who drank at least 4 cups per day had a 17% lower risk.
The relationships were shown regardless of the type of tea people drank, whether they identified as male or female, or where they resided, indicating that the quantity of tea taken may be more important than any other factor in explaining the associations.
Our results imply that drinking tea is beneficial in lowering the risk of type 2 diabetes, but only at large levels (at least 4 cups a day), adds Li. However, more research is needed to pinpoint the precise dosage and processes underlying these observations.
She continues, "It is plausible that specific tea constituents, like polyphenols, may lower blood glucose levels, but it may need a significant quantity of these bioactive substances to be effective. It may also be the reason why, despite looking at higher tea intake, we did not discover a link between type 2 diabetes and tea drinking in our cohort analysis.
The same plant that is used to produce green and black teas is also used to manufacture oolong tea, a traditional Chinese beverage. The processing method makes a difference; oolong tea is partially oxidised whereas black tea is permitted to fully oxidise. Green tea is not allowed to oxidise substantially.
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Despite the significant results, the authors point out that as the research was observational, it cannot conclusively show that tea consumption decreased the incidence of T2D but rather provides evidence that it probably does.
The researchers also highlight a number of cautions, such as the fact that they relied on estimates of the amounts of tea consumed that were made subjectively, and that they cannot completely rule out the possibility that residual confounding from other lifestyle and physiological factors may have impacted the findings.