Does cranberry juice really prevent or treat urinary tract infections (UTIs)?

The short answer is, "probably not". So is this another one of those medical myths, then? I had a patient's relative ask me this question recently. They had driven up from Sarasota to see me for some other nephrological issue, when we got talking about the role of recurrent kidney infections in causing chronic kidney disease (CKD). Recurrent kidney infections (called pyelonephritis, which is a type of a UTI) are known to cause renal scarring. They might also be associated with genetic or developmental abnormalities that could be lead to CKD.  That is a separate discussion in itself, but for the time being, I wanted to delve a little bit in to whether cranberry juice is worth your money. This is another one of those "top ten" questions that nephrologists get all the time!

Do cranberries prevent UTIs?
Image courtesy of James Barker/FreeDigitalPhotos.net

Jokes about cranberry juice aside, there do seem to be plausible biological mechanisms to suggest that it should prevent recurrent UTIs, and we do have basic scientific studies that support that.
Hence, till pretty recently, 2012 to be exact, the official medical recommendation was that cranberry juice could prevent UTIs. However, this recommendation was based on poorly designed, half-baked clinical studies. Then, in 2012, a group published new data (called a meta-analysis), taking in to account the evidence provided by some of the later larger studies. This meta-analysis clearly showed that not only was the benefit, if at all, was very small, it also was not much better than taking antibiotics. There were problems noted with most studies, including the fact that it is hard to quantify the "active ingredient" in cranberry juice that possibly prevents UTIs, and all cranberry juice preparations may not have the same amount of this active ingredient. It is also possible that you would need to drink gallons of juice to see a real benefit, but that would mean taking a huge amount of sugar and calories, thus doing more harm than good. Finally, cranberry juice actually increases the risk of forming a kidney stone! This is a well established medical fact, and happens because of a marked increase in the urine excretion of oxalate. I have discussed in my previous articles about how oxalate is one of the strongest risk factors for kidney stone formation. 

There even was a time when most patients and doctors felt, "Oh, lets try it anyway. It is not going to hurt"! But now, given the above concerns, it is hard to justify a home remedy that may or may not work in preventing UTIs, but definitely comes with an increased risk of kidney stone formation, and all the dangers of increased calorie intake. Hence, cranberry juice is no longer recommended for prevention of UTIs. They say never say never in medicine; so yes, the evidence might change again in the future. But for now, I wouldn't recommend cranberry juice as a preventive remedy for UTIs to anyone.