I’ve never read that proanthocyanidins prevent bacterial adhesion, but I’ll take your word on that.

Here’s your confounder for UTI prevention: When my wife skips the proanthocyanidins by taking powdered mannose sugar instead of cranberries or cranberry juice (which have both), her UTIs no longer occur.

She is not willing to try only proanthocyanidins as a control. And I am not willing to return to the $200 bills for the 2am trips to the ER across town either.

You may be right about mannose, but I’m not vouching for that here. As far as I know, the mannose work and concentration is in other fruit juices.

You are certainly right about the issue being confusing,and confused by assumptions about what is being talked about. I addressed this here: http://scienceblogs.com/gregladen/2010/08/13/does-cranberry-juice-help-repr/

Cranberry happens to be high in mannitol, which converts readily to mannose, some of which is excreted in the urine. By eating cranberries, or cranberry extract, one’s level of urinary mannose increases.

Once in the bladder, the aqueous mannose competes with human bladder cells for attachment to UTI bacteria. By reducing the number of available, unbound mannose binding sites on the UTI bacteria, fewer bacteria attach and can form biofilms. The bacteria are then excreted by urination.

One can “cut to the chase” and simply ingest powdered mannose sugar to achieve the same effect. Eating cranberries is not necessary, although they’re likely to be more available than bottles of powdered mannose…

One of things that confuses this issue is the incorrect assumption that what’s labeled as “cranberry juice” in the grocery stores actually contains cranberry juice — or, mannitol/mannose, which is what’s important. Typically, this is not the case, and if this were the basis of experiments to verify its efficacy, it will likely fail.

Another misconception is that cranberry/mannose is an effective treatment for UTIs. It is NOT. Once the UTI bacteria form biofilms on the bladder walls, it’s “game over” — you have an infection and it’s too late.

Cranberry/mannose is only effective as a prophylactic against getting UTIs — so it must be consumed regularly. Think of it like “birth control pills for UTI bacteria”… Skip your dose and you may have “unhappy result”.

I quickly add: cranberry juice is not known to be good at treating UTIs. The question is, does regular consumption of the juice reduce recurrence of UTI’s in women who tend to get them easily. The available evidence suggests that this may be true, but it is not conclusively proven. The cranberry juice thing is more interesting because of what it reveals about how regular people as well as scientists react to incomplete information. See this: http://scienceblogs.com/gregladen/2010/08/13/does-cranberry-juice-help-repr/