Cranberries ineffective for preventing urinary tract infections (but still nice with turkey)

Remember when Delia Smith put cranberries in all those winter recipes, creating such a demand for them that they were the 1995 equivalent of the iPhone 5, if with a little less functionality? If domestic goddesses were excited by the thought of putting this fruit where previously there’d only been sage and onion, others bought into cranberry juice, and other cranberry products, in the hope that making this their regular tipple would help stop them getting urinary tract infections (UTIs).

People have long believed in the usefulness of cranberries in keeping their bladders squeaky clean, and whilst there are various theories on how cranberries might prevent UTIs, one is that they prevent bacteria from sticking to the bladder walls. A Cochrane review on the effectiveness of cranberry products in preventing UTIs first appeared in 1998 and, back then, things were looking quite hopeful with respect to the humble cranberry. This review has now been updated for the third time and with the addition of evidence from 14 new studies it seems that cranberry juice and other cranberry products don’t offer any significant benefit in preventing UTIs after all.

The evidence comes from 24 studies involving 4,473 people, with more evidence available for adult women than the other ‘at risk’ subgroups, such as the very young and the elderly, pregnant women and people having radiation therapy. Intervention groups were given cranberries as juice, tablets or capsules and were compared with control groups having placebo products, water, antibiotics, methenamine hippurate (an antibacterial medicine), lactobacillus or nothing.

Here’s what they found:

  • In some small studies, there were slightly fewer UTIs amongst women taking cranberry products compared to those taking nothing or placebo. This benefit wasn’t seen once the results of the newest and largest study were added
  • No benefit of cranberry products over placebo or nothing was seen in any other subgroups
  • Three small studies looked at cranberry products versus antibiotics and found no significant difference
  • Many people stopped taking cranberry, especially in juice form, and dropped out of the studies

Some limitations to bear in mind:

  • Most studies were small and lacked statistical power to detect significant differences between groups
  • Many people involved in the studies at the start were not included in the final analyses, which may have biased the results
  • There was a lack of information about the amount of active ingredient in cranberry products

The authors concluded:

Given the large number of dropouts/withdrawals from studies (mainly attributed to the acceptability of consuming cranberry products particularly juice, over long periods), and the evidence that the benefit for preventing UTI is small, cranberry juice cannot currently be recommended for the prevention of UTIs.

So now what?

The authors do not think that further research into cranberry juice for preventing UTIs can be recommended, and say that care needs to be taken in any future testing of other cranberry products, ensuring they contain enough of the ‘active’ ingredient, before being evaluated in clinical studies or recommended for use.

So not much good news there but, whilst cranberries might not be our bladders’ best friends, they do make awfully good chutney.

 Links:

Jepson RG, Williams G, Craig JC. Cranberries for preventing urinary tract infections. Cochrane Database of Systematic Reviews 2012, Issue 10. Art. No.: CD001321. DOI: 10.1002/14651858.CD001321.pub5.

Cochrane summary and podcast of this review.

 

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Sarah Chapman

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My name is Sarah Chapman. I have worked on systematic reviews and other types of research in many areas of health for the past 17 years, for the Cochrane Collaboration and for several UK higher education institutions including the University of Oxford and the Royal College of Nursing Institute. I also have a background in nursing and in the study of the History of Medicine.

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