Cranberries for preventing urinary tract infections.

BACKGROUND: Cranberries (particularly in the form of cranberry juice) have been used widely for several decades for the prevention and treatment of urinary tract infections (UTIs). The aim of this review is to assess the effectiveness of cranberries in preventing such infections.

OBJECTIVES: To assess the effectiveness of cranberry juice and other cranberry products in preventing UTIs in susceptible populations.

SEARCH STRATEGY: Electronic databases and the Internet were searched using English and non English language terms; companies involved with the promotion and distribution of cranberry preparations were contacted; reference lists of review articles and relevant trials were searched.

SELECTION CRITERIA: All randomised or quasi randomised controlled trials of cranberry juice/products for the prevention of urinary tract infections in susceptible populations. Trials of men, women or children were included.

DATA COLLECTION AND ANALYSIS: Two reviewers independently assessed and extracted information. For each included trial, information was collected on methods, participants, interventions and outcomes (urinary tract infections (symptomatic and asymptomatic), side effects and adherence to therapy). We were unable to perform statistical analysis due to the nature of the data available for review, so a narrative synthesis was undertaken. Quality was assessed using the Cochrane criteria.

MAIN RESULTS: Five trials met the inclusion criteria (four cross-over, one parallel group). Four compared the effectiveness of cranberry juice versus placebo juice or water, and one compared the effectiveness of cranberry capsules versus placebo. Two further trials were excluded. Data from two out of the five trials indicated that cranberries were effective for either symptomatic or asymptomatic UTIs, but this result was not obtained in an intention-to-treat analysis. Side effects were common, and dropouts high. Overall, the quality of the five included trials was poor, the sample sizes were small, and thus the reliability of the results must be questionable.

REVIEWER'S CONCLUSIONS: The small number of poor quality trials gives no reliable evidence of the effectiveness of cranberry juice and other cranberry products. The large number of dropouts/withdrawals from the trials indicates that cranberry juice may not be acceptable over long periods of time. There is no conclusive evidence to recommend cranberry juice for the prevention of UTIs. Further properly designed trials with relevant outcomes are needed.