Cranberry juice has long been touted as offering relief for urinary tract infections (UTIs), which affect more than 50% of women at least once, a third of them developing recurrent infections. Now, new evidence says that the juice can, in fact, reduce the risk of recurrent infection.
The meta-analysis by Australian researchers of almost 9 000 people confirms cranberry’s reputation as a helpful supplement for people wanting to avoid recurrent UTIs.
The authors said their findings showed cranberry’s protective effect was evident in women, children and people vulnerable to UTIs after medical interventions, reports Medical News Today.
While cranberry has, for years, been regarded as a preventive or curative treatment for UTIs, until now, research has produced conflicting evidence of this.
The global study by the scientists at Flinders University and The Children’s Hospital at Westmead in Australia is the fifth update of a review first released in 1998 and last updated in 2012, and was published in Cochrane Reviews.
Prof Jonathan Craig, the study’s senior author, said the research “shows a very positive finding that cranberry juice can prevent UTI in susceptible people.”
E. coli and UTIs
UTIs develop when bacteria enter and infect the urinary tract, which includes the urethra, bladder, ureter and kidney.
The growth of Escherichia coli (E. coli) in the urinary tract is the most common cause of UTIs.
This bacteria strain is naturally present in the gut but can travel into the bladder through contamination of faecal matter. It then sticks to the bladder walls and reproduces.
Polyphenols, cranberries’ power punch
Antibiotic prescriptions are the prevailing prevention and treatment protocol – contributing to the rise of medication-resistant pathogens.
Cranberry contains proanthocyanidins (PAC), a type of polyphenol. These “offence and defence” nutrients hold remarkable antimicrobial and antioxidant potential.
In a 2022 research article, Canadian researchers found that PAC may help inhibit the formation of bacterial biofilm in the urinary tract lining. They also showed that PAC might deter activation of uropathogenic E. coli “virulence genes at an early stage in the gut reservoir”.
Analysis of 50 studies
The researchers combed through the Cochrane Kidney and Transplant Specialized Register up to March 2023, analysing results from randomised controlled trials of cranberry products compared with placebos, intervention with antibiotics or probiotics, or no specific treatment for UTI prevention.
The team added 26 new studies to this update, bringing the total number of studies to 50 with 8 857 participants.
“The studies we reviewed included various methods to determine the benefits of cranberry products,” said Stephens. “Most compared cranberry products with a placebo or no treatment for UTI and determined drinking cranberries as a juice or taking capsules reduced the number of UTIs in women with recurrent cases, in children, and in people susceptible to UTIs after medical interventions like bladder radiotherapy.”
Cranberry benefits
The authors found cranberry product consumption was strongly associated with a reduced risk of symptomatic, culture-verified UTIs in women with recurrent UTIs and showed significant protective benefit in children and people at risk of UTIs due to interventions like bladder radiotherapy.
It was unclear whether cranberry juice, tablets, or different doses of PAC were more effective against UTIs.
Few people reported side effects from consuming cranberry products. The most common adverse reaction was stomach upset.
Limited data
The research team said further studies are needed to determine which population with UTI would benefit the most from cranberry juice.
“Currently available data was either limited or inconclusive for the use of cranberry products for the prevention of UTIs for pregnant women, the elderly, or people with bladder problems,” said Stephens. “More data are required to be able to provide definitive advice about whether cranberry might be suitable for these groups.”
Some experts not convinced
Urologist Dr Jennifer Linehan, an associate professor of urology and urologic oncology at the Saint John’s Cancer Institute at Providence Saint John’s Health Centre in Santa Monica, who was not involved in this research, was concerned that the sugar content in many cranberry juice products makes them unhelpful for preventing UTIs.
However, she noted that “cranberry itself can help when taken in powder form because it can block the bacteria from binding to the bladder but on occasion, can irritate the bladder lining”.
Another urologist Dr Adam Ramin, medical director of Urology Cancer Specialists in Los Angeles, said that “100% pure cranberry juice may aid in (the) treatment of low-grade, not very serious type of UTIs”.
“However, pure cranberry juice is very tart and sour. Most people cannot tolerate drinking it.”
Study details
Cranberries for preventing urinary tract infections
Gabrielle Williams, Deirdre Hahn, Jacqueline Stephens, Jonathan Craig, Elisabeth Hodson.
Published in Cochrane Library on 16 April 2023
Abstract
Background
Cranberries contain proanthocyanidins (PACs), which inhibit the adherence of p‐fimbriated Escherichia coli to the urothelial cells lining the bladder. Cranberry products have been used widely for several decades to prevent urinary tract infections (UTIs). This is the fifth update of a review first published in 1998 and updated in 2003, 2004, 2008, and 2012.
Objectives
To assess the effectiveness of cranberry products in preventing UTIs in susceptible populations.
Selection criteria
All randomised controlled trials (RCTs) or quasi‐RCTs of cranberry products compared with placebo, no specific treatment or other intervention (antibiotics, probiotics) for the prevention of UTIs were included.
Data collection and analysis
Two authors independently assessed and extracted data. Information was collected on methods, participants, interventions and outcomes (incidence of symptomatic UTIs, positive culture results, side effects, adherence to therapy). Risk ratios (RR) with 95% confidence intervals (CI) were calculated where appropriate. Study quality was assessed using the Cochrane risk of bias assessment tool. Confidence in the evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.
Main results
For this update 26 new studies were added, bringing the total number of included studies to 50 (8857 randomised participants). The risk of bias for sequence generation and allocation concealment was low for 29 and 28 studies, respectively. Thirty‐six studies were at low risk of performance bias, and 23 studies were at low risk of detection bias. Twenty‐seven, 41, and 17 studies were at low risk of attrition bias, reporting bias and other bias, respectively.
Forty‐five studies compared cranberry products with placebo or no specific treatment in six different groups of participants. Twenty‐six of these 45 studies could be meta‐analysed for the outcome of symptomatic, culture‐verified UTIs. In moderate certainty evidence, cranberry products reduced the risk of UTIs (6211 participants: RR 0.70, 95% CI 0.58 to 0.84; I² = 69%). When studies were divided into groups according to the treatment indication, cranberry products probably reduced the risk of symptomatic, culture‐verified UTIs in women with recurrent UTIs (8 studies, 1555 participants: RR 0.74, 95% CI 0.55 to 0.99; I² = 54%), in children (5 studies, 504 participants: RR 0.46, 95% CI 0.32 to 0.68; I² = 21%) and in people with a susceptibility to UTIs due to an intervention (6 studies, 1434 participants: RR 0.47, 95% CI 0.37 to 0.61; I² = 0%). However, in low certainty evidence, there may be little or no benefit in elderly institutionalised 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 neuromuscular bladder dysfunction with incomplete bladder emptying (3 studies, 464 participants: RR 0.97, 95% CI 0.78 to 1.19; I² = 0%).
Other comparisons were cranberry products with probiotics (three studies) or antibiotics (six studies), cranberry tablets with cranberry liquid (one study), and different doses of PACs (two studies).
Compared to antibiotics, cranberry products may make little or no difference to the risk of symptomatic, culture‐verified UTIs (2 studies, 385 participants: RR 1.03, 95% CI 0.80 to 1.33; I² = 0%) or 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 products may reduce the risk of symptomatic, culture‐verified UTIs (3 studies, 215 participants: RR 0.39, 95% CI 0.27 to 0.56; I = 0%). It is unclear whether efficacy differs between cranberry juice and tablets or between different doses of PACs as the certainty of the evidence was very low.
The number of participants with gastrointestinal side effects probably does not differ between those taking cranberry 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 compliance with therapy and the risk for repeat UTIs. No difference in the risk for UTIs could be demonstrated between low, moderate and high doses of PACs.
Authors’ conclusions
This update adds a further 26 studies taking the total number of studies to 50 with 8857 participants. These data support the use of cranberry products to reduce the risk of symptomatic, culture‐verified UTIs in women with recurrent UTIs, in children, and in people susceptible to UTIs following interventions. The evidence currently available does not support its use in the elderly, patients with bladder emptying problems, or pregnant women.
Cochrane Library article – Cranberries for preventing urinary tract infections (Open access)
See more from MedicalBrief archives:
Cranberries could improve memory, fight dementia – British collaborative study
E. coli from raw meat causes one in 14 UTIs – US study
Most women receive inappropriate treatment for uncomplicated UTIs
Early antibiotics for elderly with UTI linked to reduced sepsis risk