Cranberries and Urinary Tract Infections
By Dónal P. O'Mathúna, PhD. Dr. O'Mathúna is Senior Lecturer in Ethics, Decision-Making & Evidence, School of Nursing, Dublin City University, Ireland; he reports no financial relationships to this field of study.
Source: Jepson RG, Craig JC. Cranberries for preventing urinary tract infections. Cochrane Database Syst Rev 2008;1:CD001321.
Cranberries have been used widely for several decades for the prevention and treatment of urinary tract infections (UTIs).
Objectives: To assess the effectiveness of cranberry products in preventing UTIs in susceptible populations.
Search strategy: The investigators searched MEDLINE, EMBASE, the Cochrane Central Register of Controlled Trials (CENTRAL in The Cochrane Library), and the Internet. They contacted companies involved with the promotion and distribution of cranberry preparations and checked reference lists of review articles and relevant studies. Date of last search: January 2007.
Selection criteria: All randomized controlled trials (RCTs) or quasi-RCTs of cranberry products for the prevention of UTIs in all populations.
Data collection and analysis: Two authors independently assessed and extracted information. Information was collected on methods, participants, interventions, and outcomes (UTIs: symptomatic and asymptomatic, side effects, adherence to therapy). Relative risks (RR) were calculated where appropriate, otherwise a narrative synthesis was undertaken. Quality was assessed using the Cochrane criteria.
Main results: Ten studies (n = 1049, five crossover, five parallel group) were included. Cranberry/cranberry-lingonberry juice vs. placebo, juice, or water was evaluated in seven studies, and cranberries tablets vs. placebo in four studies (one study evaluated both juice and tablets). Cranberry products significantly reduced the incidence of UTIs at 12 months (RR 0.65; 95% confidence interval, 0.46-0.90) compared with placebo/control. Cranberry products were more effective reducing the incidence of UTIs in women with recurrent UTIs than in elderly men and in women or people requiring catheterization. Six studies were not included in the meta-analyses due to methodological issues or lack of available data. However, only one reported a significant result for the outcome of symptomatic UTIs. Side effects were common in all studies, and dropouts/withdrawals in several of the studies were high.
Authors' conclusions: There is some evidence that cranberry juice may decrease the number of symptomatic UTIs over a 12-month period, particularly for women with recurrent UTIs. Its effectiveness for other groups is less certain. The large number of dropouts/withdrawals indicates that cranberry juice may not be acceptable over long periods of time. It is not clear what is the optimum dosage or method of administration (e.g., juice, tablets, or capsules). Further properly designed studies with relevant outcomes are needed.
Commentary
Urinary tract infections are one of the most common conditions for which outpatient treatment is sought. Approximately half of all women will get a UTI at some point in their lives, and 20% of women between the ages of 20 and 56 get one UTI annually.1 The term UTI covers a range of infections in different parts of the urinary tract, all characterized by high bacteria counts in the urine (usually greater than 100,000/mL). UTIs occur about 50 times more often in adult women than adult men, probably due to women's urethras being shorter which allows bacteria to ascend into the bladder more easily. Most women who get a UTI will experience another, and 25% will suffer recurrent infections.2 Conventional treatment for UTIs is antibiotics, but rising clinical failure rates and antibiotic resistance have led to interest in alternative strategies to preventing and treating UTI.
Cranberry juice has long been used to prevent and treat UTIs. The authors of this Cochrane review had previously published a review of cranberry juice as a treatment for UTIs.3 That review (last updated in 2007) found no controlled studies that met their inclusion criteria. Clinical trials are currently being conducted on the use of cranberry juice in treating UTIs, but currently evidence to support its effectiveness does not exist.2
The Cochrane review reported here focused on the use of cranberry to prevent UTIs. A broad search strategy was used to capture studies of cranberry juice and tablets or capsules containing cranberries. The latter have become popular because of the disagreeable taste of cranberry juice. The search strategy also included the terms for cranberry and UTI in seven other languages to increase the chances of identifying non-English language studies. The reviewers also contacted the manufacturers of cranberry products in an attempt to locate other studies.
The first controlled study of cranberry juice was published in the Journal of the American Medical Association in 1994.4 Elderly women who daily drank 300 mL of cranberry juice had fewer UTIs than those drinking a similar-tasting red drink. In contrast, a 1999 controlled study with children at high risk for UTIs did not find different rates of infection between those drinking cranberry and a placebo drink. Such differences may arise from the different types of UTIs experienced by different groups of people. The Cochrane review reported here took these differences into account by analyzing the findings according to predetermined subgroups. Six categories of people at higher risk of UTIs were developed: women with recurrent UTIs, elderly men and women, participants needing intermittent catheterization, pregnant women, participants with an in-dwelling catheter, and participants with a urinary tract abnormality. Studies that met the inclusion criteria were not located for all categories.
The results of this Cochrane review provide some evidence for the use of cranberry products in preventing UTIs over 12 months, especially for women with recurrent UTIs. Limited efficacy was found for older men and women, confirming that cranberries may not be effective for all groups of people. Some of the studies, including the largest, involved participants with asymptomatic UTIs.4 The reviewers noted that "even if cranberry juice is effective in preventing asymptomatic UTIs, it is a condition which does not normally need treating in certain populations."
An important limitation identified is the lack of information on dosage. The amount of juice used in the studies varied from 30 mL/d to 300 mL/d. No rationale was given for the amounts selected. Of the four studies using cranberry supplements, two used capsules containing 400 mg of cranberry solids, one used capsules containing 2 g concentrated juice, and one used tablets containing juice concentrate. Products are not standardized against an active ingredient, believed to be a group of proanthocyanidins.
While the review did not identify serious adverse effects with cranberry juice, the number of withdrawals in some studies was of concern (20%-55% of participants). This was often due to the juice's taste. This is problematic given that the juice is recommended daily for long periods of time. While several tablet and capsule formulations are now available, evidence for their effectiveness is limited. Nevertheless, the review demonstrates that evidence does support the use of cranberry juice to prevent UTIs among women with recurrent UTIs.
References
1. Franco AV. Recurrent urinary tract infections. Best Pract Res Clin Obstet Gynaecol 2005;19:861-873.
2. Howell AB. Bioactive compounds in cranberries and their role in prevention of urinary tract infections. Mol Nutr Food Res 2007;51:732-737.
3. Jepson RG, et al. Cranberries for treating urinary tract infections. Cochrane Database Syst Rev 1998;4:CD001322.
4. Avorn J, et al. Reduction of bacteriuria and pyuria after ingestion of cranberry juice. JAMA 1994;271: 751-754.
O’Mathuna D. Cranberries and Urinary Tract Infections. 2008;10:77-78.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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