Cranberry: Confirmed Reduction of Urinary Tract Infections from Study
Cranberries contain proanthocyanidins (PACs) that inhibit the adhesion of p-fimbriated Escherichia coli to urothelial cells lining the bladder. Cranberry-based products have been widely used for several decades to prevent urinary tract infections (UTIs). This is the fifth update of a review first published in 1998 and subsequently updated in 2003, 2004, 2008, and 2012.
The study aimed to evaluate the efficacy of cranberry-based products in preventing UTIs in susceptible populations.
A search was conducted in the Cochrane Kidney and Transplant specialized register until March 13, 2023, contacting the Information Specialist and using relevant search terms for this review. Studies in the register were identified through searches in CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Registry Platform (ICTRP) search portal, and ClinicalTrials.gov.
All randomized controlled trials (RCTs) or quasi-RCTs on cranberry-based products compared to placebo, no specific treatment, or other interventions (antibiotics, probiotics) for preventing urinary tract infections were included.
Two authors independently assessed and extracted data. Information on methods, participants, interventions, and outcomes (incidence of symptomatic UTIs, positive culture outcomes, side effects, therapy adherence) was collected. Risk ratios (RRs) with 95% confidence intervals (CIs), where appropriate, were calculated. Study quality was assessed using the Cochrane Risk of Bias tool. Evidence confidence was evaluated using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.
This update added 26 new studies, bringing the total number of included studies to 50 (8857 randomized participants). The risk of bias for sequence generation and allocation concealment was low for 29 and 28 studies, respectively.
Thirty-six studies had low risk of performance bias, and 23 studies had low risk of detection bias.
Twenty-seven, 41, and 17 studies had low risk of attrition bias, reporting bias, and other biases, respectively.
Forty-five studies compared cranberry-based products with placebo or no specific treatment in six different participant groups.
Twenty-six out of these 45 studies could be meta-analyzed for the outcome of symptomatic urinary tract infections confirmed by culture.
With moderate-certainty evidence, cranberry-based products reduced the risk of UTI (6211 participants: RR 0.70, 95% CI 0.58 to 0.84; I² = 69%).
When studies were subgrouped by treatment indication, cranberry-based products likely reduced the risk of symptomatic UTIs confirmed by culture in women with recurrent UTIs (8 studies, 1555 participants: RR 0.74, 95% CI 0.55-0.99; I² = 69%), in children (5 studies, 504 participants: RR 0.46, 95% CI 0.32 to 0.68; I² = 21%), and in individuals susceptible to UTIs due to an intervention (6 studies, 1434 participants: RR 0.47, 95% CI 0.37 to 0.61; I² = 0%).
However, based on low-certainty evidence, there might be little or no benefit in institutionalized elderly men and women (3 studies, 1489 participants: RR 0.93, 95% CI 0.67 to 1.30; I² = 9%), pregnant women (3 studies, 765 participants: RR 1.06, 95% CI 0.75 to 1.50; I² = 3%), or adults with neurogenic bladder dysfunction with incomplete emptying (3 studies, 464 participants: RR 0.97, 95% CI 0.78 to 1.19; I² = 0%).
Other comparisons were cranberry-based products with probiotics (three studies) or antibiotics (six studies), cranberry tablet versus cranberry juice (one study), and different doses of PAC (two studies). Compared to antibiotics, cranberry-based products may make little or no difference in the risk of symptomatic UTIs confirmed by culture (2 studies, 385 participants: RR 1.03, 95% CI 0.80 to 1.33; I² = 0%) or in the risk of clinical symptoms without culture (2 studies, 336 participants: RR 1.30, 95% CI 0.79 to 2.14; I² = 68%).
Compared to probiotics, cranberry-based products may reduce the risk of symptomatic UTIs confirmed by culture (3 studies, 215 participants: RR 0.39, 95% CI 0.27-0.56; I = 0%). It’s unclear if the effectiveness differs between cranberry juice and tablets or between different doses of PAC due to very low evidence certainty. The number of participants with gastrointestinal side effects probably doesn’t differ between those taking cranberry-based products and those receiving placebo or no specific treatment (10 studies, 2166 participants: RR 1.33, 95% CI 1.00 to 1.77; I² = 0%; moderate-certainty evidence).
There was no clear relationship between therapy adherence and the risk of repeated UTIs. No difference in UTI risk among low, moderate, and high doses of PAC could be demonstrated.
This update adds 26 more studies, totaling 50 studies with 8857 participants. These data support the use of cranberry-based products to reduce the risk of symptomatic urinary tract infections confirmed by culture in women with recurrent UTIs, in children, and in individuals susceptible to UTIs following interventions. Currently available evidence doesn’t support their use in the elderly, patients with bladder emptying issues, and pregnant women.
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Source: Williams G, Hahn D, Stephens JH, Craig JC, Hodson EM. Cranberries for preventing urinary tract infections. Cochrane Database Syst Rev. 2023 Apr 17;4(4):CD001321. doi: 10.1002/146518