Key message: The current evidence suggests that any benefit of taking cranberry products to prevent urinary tract infection is likely to be small and people may find taking them over a long period of time unacceptable.

As garlic is to vampires, so cranberries are to urinary tract infections (UTIs); or so many people believe, drinking cranberry juice in the hope of avoiding bouts of this unpleasant complaint. Cranberry products have been used for this purpose for a very long time and though it’s unclear how they might help, one theory is that cranberries prevent bacteria from sticking to the walls of the bladder.

Up to now, there has been some Cochrane evidenceCochrane Reviews are systematic reviews. In systematic reviews we search for and summarize studies that answer a specific research question (e.g. is paracetamol effective and safe for treating back pain?). The studies are identified, assessed, and summarized by using a systematic and predefined approach. They inform recommendations for healthcare and research. to support a role for cranberries in preventing UTIs. A review first published in 1998, which looked at the effectivenessThe ability of an intervention (for example a drug, surgery, or exercise) to produce a desired effect, such as reduce symptoms. of cranberry products in preventing UTIs in people who are susceptible to them, found some evidence to show that cranberry juice can reduce the number of infections in women who tend to get them repeatedly. In the latest update of this review published today in the Cochrane Library, evidence from 14 new studies suggests that cranberry juice is less effective than previously thought.

The review now includes 24 studies with a total of 4,473 people. Adult women were the most studied, but other subgroups at riskA way of expressing the chance of an event taking place, expressed as the number of events divided by the total number of observations or people. It can be stated as ‘the chance of falling were one in four’ (1/4 = 25%). This measure is good no matter the incidence of events i.e. common or infrequent. of UTIs, such as pregnant women, children and older adults were included. People who were given cranberry juice, capsules or tablets were compared with people given water, methenamine hippurate, antibiotics, lactobacillus, placeboAn intervention that appears to be the same as that which is being assessed but does not have the active component. For example, a placebo could be a tablet made of sugar, compared with a tablet containing a medicine. products or nothing.

What did they find?

• A small trend towards fewer UTIs in women taking cranberry products compared with those taking a placeboAn intervention that appears to be the same as that which is being assessed but does not have the active component. For example, a placebo could be a tablet made of sugar, compared with a tablet containing a medicine. or nothing was shown in some small studies, but no significant differences when the results of a larger studyAn investigation of a healthcare problem. There are different types of studies used to answer research questions, for example randomised controlled trials or observational studies. were added
• No significant benefit of cranberry products compared to placeboAn intervention that appears to be the same as that which is being assessed but does not have the active component. For example, a placebo could be a tablet made of sugar, compared with a tablet containing a medicine. or no treatmentSomething done with the aim of improving health or relieving suffering. For example, medicines, surgery, psychological and physical therapies, diet and exercise changes. for any other subgroups of people at riskA way of expressing the chance of an event taking place, expressed as the number of events divided by the total number of observations or people. It can be stated as ‘the chance of falling were one in four’ (1/4 = 25%). This measure is good no matter the incidence of events i.e. common or infrequent. of UTI
• Cranberry products were not significantly different to antibiotics for preventing UTIs in three small studies
• Many people stopped taking the cranberry products, especially the juice, and dropped out of the studies

How good is the evidence?

The review authors judged the studies to be generally robust but point out some problems, including:

• a lack of information about the amount of active ingredient in cranberry capsules or tablets
• not including in the final analysis a large number of people who were allocated to treatments at the start, which can introduce biasAny factor, recognised or not, that distorts the findings of a study. For example, reporting bias is a type of bias that occurs when researchers, or others (e.g. drug companies) choose not report or publish the results of a study, or do not provide full information about a study. in the results
• most studies were small and lacked power to detect significant differences between groups

Links:

Full citation:Jepson RG, Williams G, Craig JC. Cranberries for preventing urinary tract infections. Cochrane Database of Systematic ReviewsIn systematic reviews we search for and summarize studies that answer a specific research question (e.g. is paracetamol effective and safe for treating back pain?). The studies are identified, assessed, and summarized by using a systematic and predefined approach. They inform recommendations for healthcare and research. 2012, Issue 10. Art. No.: CD001321. DOI: 10.1002/14651858.CD001321.pub5. http://doi.wiley.com/10.1002/14651858.CD001321.pub5

Funding for the 2012 update of the review was provided by the National Institute for Health Research (NIHR) (www.nihr.ac.uk)

Cochrane Summary and podcast available: http://summaries.cochrane.org/CD001321/cranberries-for-preventing-urinary-tract-infections

Podcast by Ruth Jepson: http://www.cochrane.org/podcasts/issue-10-october-2012/cranberries-preventing-urinary-tract-infections

Wiley Science Newsroom has highlighted this review and you can read the press release here.

The Independent: http://www.independent.co.uk/life-style/health-and-families/health-news/cranberry-juice-is-not-effective-against-cystitis-say-scientists-8214479.html

WebMD.com: http://www.webmd.com/news/20121016/cranberries-unlikely-prevent-utis?src=RSS_PUBLIC

BBC News Scotland: http://www.bbc.co.uk/news/uk-scotland-19976651

ABC News: http://abcnews.go.com/Health/Wellness/cranberry-juice-good-bladder-infections/story?id=17492426

The Herald Scotland: http://www.heraldscotland.com/news/health/cranberry-juice-does-not-prevent-infection.19164468

CBS News: http://www.cbsnews.com/8301-204_162-57534500/cranberries-may-not-be-effective-against-utis/

Science Daily: http://www.sciencedaily.com/releases/2012/10/121016204143.htm

News Medical: http://www.news-medical.net/news/20121017/Value-of-cranberries-for-UTI-prevention-called-into-question.aspx

Med Page Today: https://www.medpagetoday.com/Urology/Urology/35357

Medical Xpress: http://medicalxpress.com/news/2012-10-cranberry-juice-cystitis.html

The Daily Telegraph: http://www.telegraph.co.uk/health/healthnews/9631039/Cranberry-juice-offers-little-protection-against-cystitis.html