Drinking dark tea every day may reduce the risk of type 2 diabetes in adults through better blood sugar control, according to a new study conducted by a team of researchers co-led by the University of Adelaide.
Picture by Petr Sidorov.
The study found daily consumers of dark tea had a 53 per cent lower risk for prediabetes and a 47 per cent reduced risk for type 2 diabetes, compared with people who had never drunk tea.
"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," said the University of Adelaide's Associate Professor Tongzhi Wu, co-lead author of the study and Hospital Research Foundation Group Mid-Career Fellow.
"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 research team, which included experts from Southeast University in China, examined the association between both the frequency and type of tea consumption and excretion of glucose in the urine, insulin resistance, and glycaemic status.
People with diabetes often have enhanced capacity for renal glucose reabsorption, so their kidneys retrieve more glucose, preventing it from being released in their urine, which contributes to the higher blood sugar.
After accounting for differences in age, sex, and clinical and lifestyle factors, the analysis found that drinking tea every day was associated with an increase in urinary glucose excretion and a reduction in insulin resistance.
"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," said Associate Professor Wu.
The beneficial effects of drinking dark tea may come from the way teas such as Pu-erh are produced, which involves microbial fermentation.
This process may yield unique bioactive compounds (including alkaloids, free amino acid, polyphenols, polysaccharides, and their derivatives) to exhibit potent antioxidant and anti-inflammatory effects, improve both insulin sensitivity and the performance of beta cells in the pancreas, and change composition of bacteria in the gut.
Participants in the study came from eight different provinces in China, with 436 living with diabetes, 352 with prediabetes, and 1,135 had normal glucose levels.
The cohort included both non-habitual tea drinkers and those with a history of drinking only a single type of tea, and they were asked about the frequency of their tea consumption.
This was an observational study, and the authors caution that the findings therefore cannot prove drinking tea every day improves blood sugar control by increasing urinary glucose excretion and reducing insulin resistance, but suggest they are likely to contribute.
The researchers are currently conducting a double-blind, randomised trial to investigate the benefits of dark tea on blood glucose control in people living with type 2 diabetes to validate their findings.
