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20.08.2025

Black tea protects against diabetes | But without sugar or sweeteners...

If you drink a few cups of black tea every day, your risk of type-2 diabetes is 14 percent lower than if you don't drink tea. But you shouldn't add sugar to your tea - and certainly no synthetic sweeteners.

Study
Chinese diabetologists affiliated with Central South University analyzed data from nearly 382,946 British people collected as part of the Biobank project.

The Chinese were able to follow the British people for approximately 14 years. During that period, 16,100 participants were diagnosed with type 2 diabetes.

The researchers had an idea of the study participants' lifestyles. They looked for associations between tea consumption and the risk of type 2 diabetes.

Results
Drinking tea reduced the risk of type 2 diabetes. The effect was optimal with an intake of 4-5 cups of tea per day, reducing the risk of the disease by 14 percent. With even higher intakes, the effect neither diminished nor increased. It remained stable.

The researchers used statistical techniques to eliminate the effect of other factors, such as smoking and diet quality.

Click on the table for a larger version.

89 percent of the participants drank black tea. When the researchers looked only at black tea, the results were just as convincing as you see above.

This was not the case for green tea. The links between green tea and type 2 diabetes were unclear. Therefore, the researchers cannot say much about the antidiabetic effect of green tea.

The researchers also examined the effect of additives in tea. They found that milk had little detrimental effect on the protective effect of tea, and that adding sugar negated this protective effect. Adding synthetic sweeteners to tea even increased the risk of type 2 diabetes.

Mechanism
Tea drinkers were slimmer than non-tea drinkers and also had a smaller waistline—and therefore less abdominal fat. These two effects account for 60 percent of the protective effect of drinking black tea.

The researchers suspect that tea components also inhibit inflammatory markers like CRP and directly enhance insulin action.

Conclusion
"Our findings provide evidence relevant to the primary prevention of type-2 diabetes, supporting inclusion of tea consumption, particularly black tea without artificial sweeteners, as an important component of a healthy diet," the researchers write.

Source:
J Am Nutr Assoc. 2025 Sep-Oct;44(7):616-26.

More:
Green tea contains insulin booster 08.11.2008

Archives:
Insulin & Glucose Metabolism
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