Type two diabetes patients who drank the trendy drink — that can cost as little as £1.25 a can — had lower levels after just four weeks, US researchers found.

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Healthy bacteria in the fermented tea could hold the key to controlling blood glucose, they suggested.

Dr Dan Merenstein, of Georgetown University, said: “To our knowledge this is the first clinical trial examining effects of kombucha in people with diabetes.

“A lot more research needs to be done but this is very promising.”

More than 5million Brits are thought to be living with type 2 diabetes, according to Diabetes UK.

The condition causes blood sugar levels to become too high because the body produces too little of a hormone called insulin.

It can cause problems with your eyes and feet, as well as raise the risk of heart disease and stroke.

Previous research in labs and rats, as well as a small study on humans, showed kombucha may hold promise in reducing blood sugar levels.

The latest study, published in Frontiers in Nutrition, tested blood sugar levels in 12 type two diabetes patients given the drink for around a month.

They compared these to levels after drinking a similar tasting placebo in another four-week period.

Participants were given around 250ml of either drink a day. 

Blood glucose levels were lowered from 164 to 116 milligrams per deciliter over the four weeks while drinking kombucha, results showed.

Dr Chagai Mendelson, of Georgetown University, said: “We were able to provide preliminary evidence that a common drink could have an effect on diabetes. 

“We hope that a much larger trial, using the lessons we learned in this trial, could be undertaken to give a more definitive answer to the effectiveness of kombucha in reducing blood glucose levels, and hence prevent or help treat type-II diabetes.”