It's been spotted in the hands of celebrities, a murky-looking drink with an exotic name: kombucha. The beverage originally hails from China, where it first earned a reputation as a health tonic nearly 2,000 years ago.
In the U.S., kombucha has gone through several reincarnations. Its benefits haven't been proved. What has been shown, for the home-brewed versions, is that it isn't always safe.
Kombucha became popular in the 1980s among the elderly and people with HIV. The drink, at that time largely home-brewed, accrued a reputation for boosting the immune system, increasing energy, improving skin and nails, and reversing the thinning and graying of hair. The beverage was (and still is) made by adding a kombucha "mushroom" -- a pancake-shaped mass of bacteria and yeast often obtained by mail order --to black or green tea and sugar.
The mixture ferments for a week, resulting in a slightly fizzy, sweet and sour (some say undrinkable) beverage containing a long list of amino acids, B vitamins and living things: Acetobacter bacteria and Brettanomyces bruxellensis, Candida stellata, Schizosaccharomyces pombe, Torulaspora delbrueckii and other yeasts.
The commercially brewed kombucha now on store shelves is similar in looks, taste and B vitamin content, but its microorganism profiles can differ from the home-brewed form. Its current popularity probably stems from its purported probiotic properties and reputation as an immune booster, says Dr. Brent Bauer, director of the Complementary and Integrative Medicine Program at the Mayo Clinic in Rochester, Minn. Labels typically boast a shorter list of microorganisms, often Lactobacillus species and a few other bacteria known for beneficial effects on digestion.
Home-brewed kombucha has had problems. Kombucha is acidic enough to kill most harmful bacteria that might try to grow during fermentation, says Yao-wen Huang, a professor at the Center for Food Safety at the University of Georgia in Athens. But harmful molds, such as species of Aspergillus, can grow, and in unsanitary conditions, harmful bacteria can too.
The drink's reputation suffered a blow when kombucha mushrooms contaminated with anthrax led to an outbreak of skin infections in an Iranian village in the mid-1990s. Around the same time, two women in Iowa developed metabolic acidosis -- a dangerous buildup of acid in the body -- after drinking kombucha; one died.
Soon after, two Australians came down with lead poisoning after drinking kombucha fermented in a ceramic pot for six months. A similar case was reported from France this year. (Investigators surmised that the acid caused lead to leach out of the glaze.)
Several lab studies have pointed to possible benefits. In test tubes, for example, the drink appeared to kill several types of harmful bacteria. In rodents, it increased immune cell activity. A 2000 study reported that mice drinking kombucha for three years lived 26 days longer on average than mice not drinking it. A 2001 study showed that drinking kombucha for 15 days protected rats' livers from some of the toxic effects of a common painkiller, acetaminophen. And a 2003 study found that kombucha reduced DNA damage in rats exposed to lead.
But that's where the evidence ends, Bauer says. "My own philosophy is, we better wait for clinical trials."
The move toward commercial kombucha is probably good, says Dr. Sherwood Gorbach, professor of public health and medicine at Tufts University School of Medicine in Boston. "It's probably safer [than home brew]." But that may also mean it could lack the home brew's purported, if unproven, benefits.