A daily shot of kombucha a fermented tea drink may help people with Type 2 diabetes who find it hard to lower their high blood sugar levels, according to results from a small clinical trial.

The study, reported in Frontiers in Nutrition, included 12 people and showed that diabetics who drank the fermented tea drink kombucha for four weeks had lower fasting blood glucose levels compared to when they consumed a similar-tasting placebo beverage.

Kombucha is a tea fermented with bacteria and yeasts and was consumed as early as 200 BC in China. Its popularity has been bolstered by anecdotal claims of improved immunity and energy and reductions in food cravings and inflammation, but proof of these benefits has been limited.

"Some laboratory and experimental studies of kombucha have shown promise and one small study in people without diabetes showed kombucha lowered blood sugar, but to our knowledge, this is the first clinical trial examining effects of kombucha in people with diabetes," said Dan Merenstein, Professor of Human Sciences in Georgetown's School of Health and professor of family medicine at Georgetown University School of Medicine. 

"A lot more research needs to be done but this is very promising," Merenstein said.

The study had one group of people drinking about eight ounces of kombucha or placebo beverage daily for four weeks and then after a two-month period to "wash out" the biological effects of the beverages, the kombucha and placebo were swapped between groups with another four weeks of drinking the beverages. Neither group was told which drink they were receiving at the time.

Kombucha appeared to lower average fasting blood glucose levels after four weeks from 164 to 116 milligrams per deciliter while the difference after four weeks with the placebo was not statistically significant. 

The researchers also looked at the makeup of fermenting microorganisms in kombucha to determine which ingredients might be the most active. 

They found that the beverage consisted mainly of lactic acid bacteria, acetic acid bacteria, and a form of yeast called Dekkera, with each microbe present in about equal measure; the finding was confirmed with RNA gene sequencing.

"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 2 diabetes," said lead author Chagai Mendelson, at Georgetown.