Kombucha: what is in it and what studies show
What it found
Kombucha is a fermented tea drink with phenolic compounds and organic acids that vary widely between batches.
Most evidence for health effects comes from lab tests and animal studies, with very few trials in people.
What they found
Studies in people
One small study in people
One study gave kombucha daily for three months to consumers and reported normalized blood sugar in people with non-insulin-dependent diabetes, but there was no control group. The authors call for controlled clinical trials.
Animal and lab studies
Antioxidant activity in lab tests
Many lab studies found that kombucha has antioxidant activity, linked to phenolic compounds and organic acids. Most of these studies did not isolate which specific compounds were responsible, so the link can only be shown statistically.
Anticancer effects in cells
In lab tests on human cancer cells, kombucha extracts inhibited cell growth and triggered cell death pathways. The authors say these results should be interpreted with caution and firm conclusions about anticancer effects in people should not be drawn.
Antimicrobial activity in lab tests
Lab tests showed kombucha can act against harmful bacteria and spoilage microorganisms, mainly due to acetic acid and other compounds. Whether this matters in the body still needs more research.
Liver and blood sugar in animals
In animal studies, kombucha improved liver function markers and reduced blood glucose and improved lipid profiles in diabetic models. The authors say evidence is still insufficient to draw firm conclusions in humans.
Studies in people and animals
Safety concerns
Reported adverse effects include gastrointestinal problems, allergic reactions, mild liver toxicity, lactic acidosis and dental erosion, mainly with large amounts, poor hygiene or in vulnerable people. The authors say good hygiene and pH control can minimize risks.
Other findings
Composition varies widely
Kombucha is made by fermenting sweetened tea with a SCOBY, a mix of bacteria and yeast. Its content of sugars, acids, vitamins and phenolic compounds changes a lot depending on the tea, the microorganisms and the fermentation conditions.
Alcohol content
Ethanol in kombucha typically ranges from 0.007% to 2.3%, depending on sugar content, storage and fermentation time and temperature. The authors say controlling these factors is essential so the drink does not exceed the 0.5% limit for non-alcoholic beverages.
What the authors conclude
“However, the available evidence comes mostly from in vitro trials, so these results should be interpreted with caution and firm conclusions should not be drawn about anticancer effects in humans.”
Also in their conclusions
- They say that both chemical and biological hazards in kombucha can be effectively minimized through careful control and standardization of the fermentation process.
- They call for controlled clinical trials to assess the impact of kombucha consumption on human health.
- They advise that evidence-based guidelines for daily consumption should be established and communicated to consumers through product labeling.
How it was done
Kombucha has grown commercially and is often marketed for potential health benefits, but the science is scattered across different fields. The authors wanted to bring together what is known about its composition, bioactivity, production and safety.
The authors searched scientific databases including Web of Science, Scopus and PubMed for studies on kombucha, fermented tea, SCOBY, bioactive compounds, fermentation, bioactivity, functional beverages, innovation, safety and legislation. They focused on peer-reviewed articles from the last decade, plus earlier studies that gave important background.
What it can’t tell you
- Most health effect studies were done in lab tests or animals, so they cannot show what happens in people.
- The one study in people with diabetes had no control group, so it cannot show cause and effect.
- The composition of kombucha varies widely between batches, so findings from one product may not apply to another.
Who paid
- Funding
- Funded by Xunta de Galicia; Universidade de Vigo (from the PubMed record).
- Conflicts
- The authors declare no conflicts of interest.
- Authors work at
- Instituto de Agroecoloxía e Alimentación (IAA), Spain; Galicia Sur Health Research Institute (IIS Galicia Sur), Spain
The paper
- Title
- Kombucha as a Bioactive Functional Beverage: Current Evidence, Production Challenges, and Future Perspectives
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Licence
- CC BY. Words in quotation marks are the authors’; the rest is our summary.
- Cite
- Pereira AG (2026). Kombucha as a Bioactive Functional Beverage: Current Evidence, Production Challenges, and Future Perspectives. International journal of molecular sciences. doi:10.3390/ijms27062739Free full textPubMed 41898599DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error