ADELAIDE, Australia — Drinking tea daily could reduce the risk of developing Type 2 diabetes by more than a quarter, according to a new study. Compared to non-tea drinkers, individuals who drank dark tea had at least a 28-percent lower likelihood of being diagnosed with the condition. Additionally, their risk of developing prediabetes decreased by 15 percent.
The study suggests that tea enhances glucose excretion in urine, leading to improved insulin resistance and better blood sugar regulation. Given that one in 10 people in the United States is diagnosed with diabetes, predominantly Type 2 diabetes due to unhealthy lifestyles, these findings are significant.
The collaborative research, led by the University of Adelaide in Australia and Southeast University in China, highlighted that dark tea decreased the risk by nearly half (47%).
What makes dark tea better?
The researchers attribute the positive effects of dark tea to its unique production process involving microbial fermentation. This process potentially produces bioactive compounds like alkaloids, free amino acids, polyphenols, polysaccharides, and derivatives. These compounds are known for their strong antioxidant and anti-inflammatory properties, enhancing insulin sensitivity, optimizing the performance of pancreatic beta cells, and altering gut bacteria composition. While these benefits are most prominent in dark tea, other tea types also exhibit them to some extent.
The research encompassed 1,923 adults (562 men and 1,361 women between 20 and 80 years-old) across eight provinces in China. Of these participants, 436 had diabetes, 352 had prediabetes, and 1,135 exhibited normal blood glucose levels.
“The substantial health benefits of tea, including a reduced risk of cardiovascular disease and Type 2 diabetes, have been reported in several studies over recent years, but the mechanisms underlying these benefits have been unclear,” says Associate Professor Tongzhi Wu of Adelaide University in a media release. “Our findings hint at the protective effects of habitual tea drinking on blood sugar management via increased glucose excretion in urine, improved insulin resistance, and thus better control of blood sugar. These benefits were most pronounced among daily dark tea drinkers.”
The researchers explain the distinction between black tea and dark tea, emphasizing that tea classification in Asia, particularly China, is based on processing methods. For instance, green tea doesn’t undergo fermentation, whereas dark tea’s unique feature is microbial fermentation.
Incorporating factors like age, gender, ethnicity, BMI, cholesterol, alcohol consumption, smoking habits, family diabetes history, and regular exercise, the study notes that dark tea drinkers experienced a 53-percent reduced risk of prediabetes. The study participants ranged from non-habitual tea drinkers to those consistently drinking one tea type. They provided details on their tea consumption frequency and type.
Those with diabetes tend to have increased renal glucose reabsorption, meaning their kidneys retain more glucose, which then isn’t excreted in urine, leading to elevated blood sugar. Upon analyzing various factors, the study determined that daily tea consumption correlated with increased urinary glucose excretion and reduced insulin resistance when compared to those who never consumed tea.
“These findings suggest that the actions of bioactive compounds in dark tea may directly or indirectly modulate glucose excretion in the kidneys, an effect, to some extent, mimicking that of sodium-glucose co-transporter-2 (SGLT2) inhibitors, a new anti-diabetic drug class that is not only effective at preventing and treating Type 2 diabetes, but also has a substantial protective effects on the heart and kidneys,” adds Prof. Wu.
Although the research is promising, the scientists note that observational studies cannot definitively prove causation. They are currently undertaking a double-blind, randomized trial to validate their results. They also acknowledge potential biases due to other lifestyle and physiological factors that might have influenced the study’s outcomes.
This findings are published in the journal Diabetologia and were presented at the Annual Meeting of The European Association for the Study of Diabetes (EASD 2023).
South West News Service writer Jim Leffman contributed to this report.
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