But the medical establishment also recognizes cranberry juice as an effective remedy. Drinking cranberry juice can prevent cystitis and even clear up a preliminary infection. The precise mechanism has been unclear, with some suggesting it is the acidity of the juice that is responsible. In order for bacteria to establish an infection, they must stick themselves to the surface of the tissue to be infected. Small fibres, called fimbriae, on the bacterial cell wall are very important for this, as they produce the 'glue' that helps the bacteria hold on.
Cranberries contain fruit sugar, fructose, which stops some bacteria from sticking to cells.
Together with an even more effective yet hitherto unknown chemical, fructose creates a non-stick coating that foils the fimbriae. The chemical is now unmasked thanks to Amy Howell of Rutgers University in New Jersey and colleagues. It so happens that substances called proanthocyanidins, found in the juice, prevent bacterial infections. The authors have purified the chemicals from cranberries and shown that they prevent bacteria from sticking to cells from the urinary tract. So it probably won't be too long before there are cranberry extract tablets available.