The following article was published in The Conversation:

Monday’s medical myth: cranberry juice prevents bladder infections

By Michael Tam, University of New South Wales

You might eat them in a sauce alongside your Christmas turkey or drink them juiced, perhaps with a shot of vodka. But the sweet, tart cranberry is also well known as a remedy for preventing urinary tract infections (UTIs).

Cystitis – an infection and inflammation of the lining of the bladder – is the most common form of UTI, with symptoms including:

• the frequent urge to pass urine
• a stinging or burning sensation when passing urine
• smelly urine
• cloudy or blood urine
• pain in the low abdomen or pelvis.

This condition occurs frequently in women, with one in three experiencing cystitis at least once in their life. As a general practitioner, it would be unusual for me to not see a case of cystitis most weeks. In most cases, cystitis is easily treated with a course of antibiotics.

As a folk remedy with a long history among Native Americans, cranberry juice was dismissed for years by the medical establishment. But this changed in the 1980s and 1990s when it was discovered that cranberry juice contained chemicals that seemed to stop E. coli (the most common bacteria causing UTIs) from sticking to the lining of the bladder.

Conceptually, if bacteria cannot attach to the bladder lining, then it would be flushed out with the urine and thus not cause an infection.

This thinking has been popularised in the last couple of decades. Cranberry juice and capsules have been widely recommended and promoted as a treatment for preventing bladder infections, particularly for women who suffer from recurrent infections. Health literature aimed at consumers, including high-quality sources, often advise that cranberry products can be used to reduce the frequency of UTI episodes.

In such a setting, it would be natural to believe that cranberry products were a proven therapy! Indeed, I was taught in medical school that cranberry was effective, and have personally prescribed it for my patients in the past.

Curiously, although there appears to be good scientific reasons why cranberry products could work in preventing UTIs, evidence that it does in real patients has been rather murky.

A 2009 Cochrane Library systematic review, which independently analysed all the available evidence, noted that there was some evidence that cranberry products might work, but it wasn’t clear what the “optimum dosage or method or administration” was.

The large number of dropouts from the available trials also suggested that it might not have been an acceptable treatment over a longer period of time.

This review was updated in October 2012 with the inclusion of newer and larger studies. Disappointingly, this revised appraisal of the empirical evidence seems to suggest that cranberry does not reduce the likelihood of a recurrence of UTIs in women.

I doubt that we have heard the last word on cranberry and there are studies in the pipeline.

But the weight of evidence, especially those from larger and better-designed trials, points towards the likelihood that cranberry products are ineffective for preventing UTIs.

Michael Tam is a community general practitioner and consults with patients who have urinary tract infections. He otherwise does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.

This article was originally published at The Conversation.
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