Does Cranberry Juice Really Prevent Urinary Tract Infections

Is cranberry juice the silver bullet for UTI it is made out to be?

Liz West; Flickr.com; Creative Commons 2.0 License

While an otherwise perfectly healthy food, how the use of cranberry or cranberry juice came to be common place for prevention or treatment of urinary tract infections (UTIs) is not well known. Cranberries have been part of native American diet for hundreds of years.  Over time, it started to be used as a prophylactic against urinary tract infections.  Several medical studies later tried to substantiate or refute this role.

However, the evidence has been often conflicting.

WHY MIGHT CRANBERRY EXTRACT WORK?

In the 1980s, evidence emerged that cranberries or its juice/extract might inhibit adhesion of pathogenic bacteria to the lining of the urinary tract, called the epithelium.  This ability is mediated by a substance called A-type Proanthocyanidins (lets call it APCs for short!). This was the purported mechanism by which infections could either be prevented or perhaps even treated.

WHY THEN, THE QUESTIONABLE CLINICAL BENEFIT

Given this basic science evidence, it would be perfectly plausible that cranberry juice or extract should have a role in UTI prevention. However, the clinical evidence to support this has not always panned out as expected. Over the last two decades, we have seen an interesting series of studies, once after the other either supporting or refuting the role of cranberry in preventing urinary tract infections.

This is a classic example of the fact that basic science evidence does not always translate well in to clinical efficacy.

One of the biggest issues has been the problem with quantifying the amount of APCs required to prevent an infection.  Apparently, the amount of APC varies from extract to extract and even between the different varieties of cranberries.

 It is thought that the amount of APC even in supplements may not be sufficient to prevent urinate tract infections on its own.  This problem with standardization has meant that it has been hard to prove a cause and effect relationship between the use of cranberry extract and prevention of UTIs.

Theoretically, one could argue that well, lets just drink more cranberry juice to increase the intake of APC.  However, remember that would also come bundled with sugars and more calories, thus bringing it's own set of problems.  Even if you just stuck to pills containing extracts of cranberry, we know that cranberries are rich in oxalate, and ingredient that could increase the risk of kidney stone formation.

To settle the question once and for all, and as we often do in medicine, we turned to meta-analysis. This entails pooling results of multiple research studies. In 2012, the Cochrane Renal Group did just that and analyzed the results of 24 extensive studies that were designed to answer this question.

And their results failed to show any clinically significant role of cranberry juice or extract in preventing urinary tract infections.

WHAT ELSE COULD YOU TRY TO PREVENT UTIs THEN?

CONCLUSION 

Based on the body of medical evidence at this time at least, it is hard to recommend cranberry juice/extract for any preventive role in urinary tract infections.  Although ingredients like APCs are backed by biological plausibility, an insufficient non-standardized amount of this ingredient might be the reason why eating cranberries, drinking cranberry juice, are taking extract pills does not show conclusive benefit.

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