The other day I saw someone mention D-Mannose in connection with preventing UTIs. I’m really prone to getting the darn things and would be very interested in getting something that would actually help–cranberry pills are good, but it looks like this stuff might be an extract of what makes cranberry effective. Here’s one of the websites selling it. From my own searching, I couldn’t find a whole lot of information. So, Dopers, is D-Mannose actually an effective substance? Or is it just the latest overhyped miracle cure, like apple-cider vinegar or melealuca or something?
Disclaimer: IANA chemist. Or anything like that. So this is probably going to be a vast oversimplification to all the chemists out there. 
Mannose, or D-mannose, is just a sugar, like glucose, sucrose, etc. It’s not the same thing as an “extract” of cranberry, because an “extract” would include the other chemicals like vitamins, minerals, and the anthocyanins that give it its red color. And it’s not even necessarily derived from cranberries; it’s just a sugar that is found in cranberries.
Mannose is also apparently found in other fruits, but Google is swamped with references to UTIs and mannose, and it’s hard to find out anything about plain old garden-variety mannose, although I did find out that this obscure fruit that I never heard of has mannose in it. So the obvious question would be, why isn’t anybody pushing jamoon fruit for UTIs? If it has mannose in it, and mannose is the magic bullet…But they’re not. You may draw your own conclusions.
If it was me, I’d stick with what I know works–the cranberry pills–and not waste your money on D-mannose, at least, not until they come up with some clinical evidence that it actually works.
The compounds that are thought to make cranberries effective at preventing UTIs are proanthrocyanins, they prevent bacteria attaching to the wall of the bladder, the bacteria are then flushed out when you pee.
In ine with DDGs searches I looked all around and it seem virtually all the cites re efficacy in treating UTIs with this stuff are sites directly selling, or promoting the sale of this product. Some medical forum participants are asking about it and personal experiences seem pretty mixed from great to no effect. Some users report queasiness & headaches as side effects.
For some anecdotal evidence, I have suffered from recurring UTIs for the past couple of years. I have tried cranberry juice, cranberry extract capsules, and D-Mannose. The D-Mannose was by far the most effective, but recently seems to have quit working for me. Some quick research in Google scholar shows that the scientific community has been aware of mannose resistant E. coli for some time. Sucks for me anyhow.
Assuming you’re lucky enough to have a normal E. coli infection and not the nasty mutant E. coli I have, mannose has a lot of things going for it. I’ve been able to get rid of a UTI myself using it. It is commonly advertised as cheap, and while you don’t pay much for a bottle of it, the recommended doses are rather large. You can go through it pretty quickly. This may be a ploy of the manufacturers’ to make you spend more money, but I was unwilling to do trials on myself to determine the lowest effective dose.
Best of luck in your efforts to combat this; it is truly a painful condition.
Thanks for the info everyone! It’s appreciated.