But before getting to the benefit question, it should be noted that there have been case reports of negative health outcomes from kombucha. The key thing to notice here is “case reports.” These have been few and far between, despite titles like “Kombucha–toxicity alert.” To be fair, there are things to watch out for. First, the way you make kombucha is putting sugar in tea, thus there is always a risk of contamination (although it has broad-spectrum antibacterial properties, http://dx.doi.org/10.1021/jf991333m). Second, human allergies/sensitvities are varied; if you are allergic/sensitive to what the SCOBY produces, you’re going to have issues. For example: “A case of Kombucha tea toxicity.” The patient shared a bottle of kombucha with a buddy. The buddy had zero effects from the kombucha whereas the patient was up a creek for a while. One possibility is that, having a compromised immune system, the sudden influx of microbes that should in theory stimulate the immune response (see below) instead sent his body into chaos. Or perhaps it was a sensitivity to the output of the microbes. Or perhaps it had nothing to do with the kombucha and the acute toxicity was due to something else. Here is another case study “Unexplained severe illness possibly associated with consumption of Kombucha tea” Two women ended up in the ER, one of them subsequently died. The thing to note is that 115 other people had been drinking kombucha from the same source of SCOBY and were fine. The other thing to note is that this was made at home. Commercial products tend to be standardized as to potency. At home you can make it strong. Very strong. Undrinkably strong, unless one espouses the view that extra strong taste means more health benefits, which some people do. Thus this might be a case of kombucha overdose, rather than ‘cosumption’ per se. In general, the way in which the medical community approaches the question of kombucha toxicity seems to be more “science” than science, and statements such as “Consumption of Kombucha tea should be discouraged, as it may be associated with life-threatening lactic acidosis” betray a naïve approach to health/harm that, to my mind, is on par with people on the internet who claim that kombucha, or anything else, is the magic potion to cure everything that ails you. Scattered incidence of potential toxicity are about as convincing to me as scattered incidence of potential curing of illness.
But onto the science! As in the peer-reviewed, experimental kind, not the speculative kind.
One early study looked at mice living out their (sort of natural) lives without interruption in a lab (http://dx.doi.org/10.1016/S0899-9007(00)00380-4 ). The most notable effect was that the mice fed kombucha lived longer. However, this might be due more to the tea aspect of the treatment rather than kombucha per se. Still, this does tend to support the idea that kombucha is non-toxic. A study done on rats (http://www.ncbi.nlm.nih.gov/pubmed/11351863) looking at acute toxicity also failed to find any negative effects of kombucha. Indeed, not only was there no toxicity found for kombucha at “regular” does, even more “extreme” doses failed to induce toxicity (http://www.ncbi.nlm.nih.gov/pubmed/11723720) and, indeed, showed some interesting benefits, including lower stress response to cold or hypoxia, although, again, this may have had more to do with the tea part of kombucha rather than anything specific to the SCOBY.
Feeding kombucha to rats has been shown to prevent the toxicity induce by chromate(VI) which is a potent oxidant (as in causes the kind of damage that you consume antioxidants to avoid), although here again, there was no “tea only” control (http://dx.doi.org/10.1016/S0378-8741(00)00161-6 ). Similarly, kombucha reversed at least some of the problems of lead ingestion (http://www.ncbi.nlm.nih.gov/pubmed/14631833 ). Similarly, kombucha prevented toxicity due to phenol in mice (http://www.ncbi.nlm.nih.gov/pubmed/21387911 ). However, the few studies that have compared kombucha with not only water control but tea as well seem to suggest that there might be something special about kombucha. For example, although black tea, black tea with some kombucha based enzymes, and kombucha all reduced the toxicity of carbon tetrachloride (http://dx.doi.org/10.4014/jmb.0806.374 or go to http://www.jmb.or.kr/journal/viewJournal.html?year=2009&vol=19&num=4&page=397 ), the kombucha group did better than the other two groups. The authors speculate that there might be some antioxidants produced by the SCOBY that are not present in tea. Similar benefits of kombucha over tea were reported for dealing with trichloroethylene toxicity (http://dx.doi.org/10.1186/1749-8546-4-23 ). The importance of this finding is that trichloroethylene is a common industrial solvent which does all manner of damage to the human body. On a more mundane yet perhaps also more relevant to daily life level, kombucha was found to not only more effective than tea at ulcers (in mice) its efficacy was on par with omeprazole, aka Prilosec (http://dx.doi.org/10.1039/C0FO00025F ). Although the authors suggest that this could have been due to kombucha reducing gastric acid release, another possibility is that the effects were more at the source, as kombucha inhibits the growth of Helicobacter pylori (http://dx.doi.org/10.1021/jf991333m), which is the bacterium responsible for ulcers in humans. Finally, kombucha was recently found to improve outcomes for diabetic rats (http://dx.doi.org/10.1186/1472-6882-12-63 ), in terms of blood sugar and blood lipid content. Again, kombucha was found to be better than just plain black tea.
So there you have it. Kombucha is unlikely to harm you and could potentially keep you in better health. If nothing else, it is certainly a very tasty drink and definitely healthier than chugging a soda.