To clarify the connection between tea consumption and the risk of developing type 2 diabetes in the future, researchers carried out a cohort study and a dose-response meta-analysis.
Washington: A study involving more than a million people from eight nations found that drinking black, green, or oolong tea in moderation is associated with a lower risk of developing type 2 diabetes. The results suggest that drinking at least four cups of tea per day is associated with a 17% lower risk of type 2 diabetes (T2D) over an average period of 10 years, according to research presented at this year’s European Association for the Study of Diabetes (EASD) Annual Meeting in Stockholm, Sweden (19–23 September).
According to lead author Xiaying Li of Wuhan University of Science and Technology in China, “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.” Because of the numerous antioxidant, anti-inflammatory, and anticarcinogenic compounds that tea contains, it has long been known that drinking tea regularly may be healthy. Still, the link between tea consumption and the risk of T2D has been less clear. Cohort studies and meta-analyses published so far have presented conflicting results.
Researchers conducted a cohort study and a dose-response meta-analysis to clarify the connection between tea consumption and future T2DM risk.
First, they looked at 5,199 adults (2583 men and 2616 women; average age, 42) from the China Health and Nutrition Survey (CHNS) who were enrolled in 1997 and followed up in 2009 and had no prior history of T2D. The CHNS is a multicenter prospective study examining residents from nine provinces with varying socioeconomic conditions and physical and mental health.
Participants initially completed questionnaires about their food and drink intake and lifestyle choices, including how often they exercised, smoked, and drank. 2,379 (46%) participants reported drinking tea overall and 522 (10%) participants had T2D by the end of the study. Researchers discovered that tea drinkers and non-drinkers had relative risks of developing T2D after controlling for variables such as age, sex and physical inactivity that are known to be associated with increased risk of T2D. And when participants who developed diabetes during the first three years of follow-up were excluded or the results were broken down by age and sex, they did not significantly alter the findings.
The researchers then reviewed all cohort studies until September 2021 that examined the relationship between tea consumption and the risk of T2D in adults (aged 18 or older). The dose-response meta-analysis included 19 cohort studies totaling 10,76,311 participants from eight 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 study location (Europe and America, or Asia) over the risk of T2D.
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 associations were seen regardless of the type of tea participants drank, whether they identified as male or female, or where they lived, indicating that the quantity of tea consumed may be more important than any other factor in explaining the associations. Our results suggest that drinking tea is beneficial in lowering the risk of type 2 diabetes, but only at high doses (at least 4 cups per day), says Li. However, more research is needed to pinpoint these observations’ precise dosages and mechanisms.
She adds, “It’s possible that specific tea ingredients, like polyphenols, can lower blood sugar levels, but this effect might require a significant quantity of these bioactive substances. Additionally, the fact that we did not examine higher tea consumption may help to explain why our cohort study did not reveal a link between type 2 diabetes and tea drinking.”
The same plant used to produce green and black teas is also used to make oolong tea, a traditional Chinese beverage. The processing method makes a difference:
- Oolong tea is partially oxidized.
- Black tea is allowed to oxidize so it turns black.
- Green tea is not allowed to oxidize much.
Despite the significant results, the authors point out that since the research was observational, it cannot conclusively show that tea consumption decreased the risk of T2D but only provides evidence that it probably does.
The researchers also highlight several 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.
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