Cranberries do not treat UTIs

A recent study in JAMA again finds cranberry products little use in combating urinary tract infections (UTIs).

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As I look out the window, it's apparent autumn has come to New York--the trees are changing colors, the tourists are less inclined to linger outside taking selfies in front of the skyscrapers and garbage piles, and the menace of Halloween is in the air (memo: must find most ironic Thrift store costume I can for under $20 tomorrow, sigh). And around the corner will be THE autumn holiday: Thanksgiving--a celebration, if the adverts are to be believed, of football (you know which one I mean, Europe), family squabbles and turkey with all the trimmings, including cranberry jelly. And cranberries, naturally, brings us to the topic of...urinary tract infections (UTIs).

Like many of our 'natural' remedies, I think the idea of drinking cranberry juice for treating UTIs has been something you randomly pick up as a factoid from somewhere non-medical, first feeling a little suspicious about the claim, but then kind of accepting it in a 'well, I guess it's true' way after seeing it touted around newspapers and even from the lips of some doctors. True, in the lab, the proanthocyanidins in cranberries has been shown to block E. coli adherence to bladder cells and yes, a some studies in humans have suggested cranberry juice can help reduce incidence of UTIs, but more human studies have shown no correlation at all between cranberry products and UTI outcomes than those that do (see recent JAMA editorial here).

Yesterday, another randomized clinical trial (see the paper at JAMA) again failed to find any benefit with cranberry use for UTIs--this time using concentrated proanthocyanidins capsules. This study investigated capsule use (equivalent of 20 ounces of cranberry juice cocktail, 2 times the dose which was suggested to be effective in a previous study) in elderly women over the course of about a year. Notably, the study had 185 participants and UTIs were carefully assessed as the presence of both bacteria (at least 10^5 per mL) and white blood cells in the urine. In the absence of antibiotics, the authors found "...there was no statistically significant difference in presence of bacteriuria plus pyuria between the treatment (29.1%) and control (29.0%) groups over 1 year."

Like all studies, there are caveats--you cannot conclude anything here about the impact of the capsules on E. coli adhesion, just disease incidence; and as the study enrolled women either with or without indication of UTI at baseline, the role of capsules in preventing new infections cannot be determined. Despite this, in the editorial accompanying the study, the careful curation of clinical parameters of disease and large study size with balanced participation between the two arms were seen as pluses for the robustness of the study. And in light of other negative studies, the JAMA editor suggests that doctors should follow the data and stop proposing cranberry as a treatment option for UTIs, as it remains unproven and only spreads false authenticity through the community when repeated by professionals.

So the take home lesson? Let's keep cranberries (and other supposed folk cures for which clinical data is not supportive ('superfoods', anyone?)) out of the clinic, and instead enjoy them them at the dinner table (and in the cocktail glass) where they belong.

Michael Chao

Project Manager, Harvard TH Chan School of Public Health

I first developed an interest in bacterial pathogenesis while at Cornell University. I then earned my PhD in Biomedical and Biological Sciences from Harvard University in Eric Rubin’s laboratory, studying cell wall remodelling in Mycobacterium tuberculosis. From 2012-2015, I continued my training as a postdoctoral fellow in Matthew Waldor’s lab at Harvard Medical School, investigating the role of DNA methylation on regulating fundamental cellular processes in Vibrio cholerae.