Tea is one of the most popular beverages in the world, and it’s also one of the healthiest ones to drink. A new study adds to that, showing that tea (at least some types of tea) has another benefit when it comes to regulating sugar.

Consuming dark tea daily can potentially reduce the risk and slow down the progression of type 2 diabetes in adults by promoting improved blood sugar regulation, according to a new study. Researchers found that those who drink dark tea on a daily basis had a 53% lower risk of prediabetes and a 47% reduced risk for type 2 diabetes. But it’s not all straightforward.

There are multiple types of tea, and “dark tea” doesn’t necessarily refer to any tea that’s dark.

Dark tea, also known as “Hei Cha” in Chinese, is a type of fermented tea that originates from China. Unlike other types of tea like green, black, or oolong, dark tea undergoes a unique fermentation and aging process that can last for several months to many years. This results in a tea that has a rich, complex flavor profile and is often considered to improve with age, much like fine wine.

Black tea also undergoes full fermentation by rolling and crushing tea leaves, but dark tea achieves fermentation through the use of yeast or moulds. Pu’er tea, for example, is a black tea from China, with a 2,000-year history. This study refers specifically to dark tea.

The study, presented at the Annual Meeting of The European Association for the Study of Diabetes and yet to be published, found the fermentation process that produces dark tea helps with blood sugar control, leading to health benefits. This is because of the bioactive compounds released through tea fermentation, such as alkaloids.

Frequent consumption of tea has been linked to a decreased likelihood of various chronic diseases, such as heart disease, stroke, and specific forms of cancer, particularly those affecting the oral and digestive tracts. Looking at diabetes, a meta-study found that some studies reported benefits but not all were conclusive.

“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”, Tongzhi Wu, one of the study co-lead authors, from the University of Adelaide, said in a news release.

The benefits of tea

The study included almost 2,000 adults living in eight provinces in China. In total, 436 had diabetes, 352 prediabetes and 1,135 had normal glucose levels. Participants included both non-habitual tea drinkers and those with a history of drinking only a single type of tea. They were asked about the frequency and type of tea they drink.

The researchers looked at the link between the frequency and type of tea consumption and excretion of glucose in the urine, insulin resistance and glycemic status. People with diabetes usually have an increased capacity for renal glucose absorption. Their kidneys get more glucose, preventing it from being excreted, leading to higher blood sugar.

After accounting for differences in age, sex and lifestyle factors, the analysis showed that drinking tea every day was linked with an increase in urinary glucose excretion and a reduction in insulin resistance, which is benefficial for people with diabetes. In fact, those favorable health effects were more marked for people drinking dark tea rather than other types of tea like green or red.

“Our findings suggest that drinking dark tea every day has the potential to lessen type 2 diabetes risk and progression through better blood sugar control. When you look at all the different biomarkers associated with habitual drinking of dark tea, it may be one simple step people can easily take,” study author Zilin Sun said in a news release.

While relevant, the researchers caution that, like any other observational study, the findings don’t prove that drinking tea every day improves blood sugar control but rather suggest it’s likely to contribute to it. They are now doing a trial to investigate the benefits of dark tea on blood glucose control in people with diabetes to validate their findings.