Is cranberry juice really effective against urinary tract infections?

This bacteria strain is naturally present in the gut but can travel into the bladder.

ISLAMABAD (Web Desk) - Cranberry has long been regarded as a preventive or curative treatment for urinary tract infections (UTIs). To date, though, research has produced conflicting evidence of its effectiveness.

Scientists at Flinders University and The Children’s Hospital at Westmead in Australia recently published a global study showing that cranberry products may indeed reduce the risk of UTIs in some groups. This is the fifth update of a review first released in 1998 and last updated in 2012. It appears in Cochrane Reviews. Prof. Jonathan Craig, the study’s senior author, says that his team’s 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 fecal matter. It then sticks to the bladder walls and reproduces.

Dr. Gabrielle Williams, the lead author of the study, told Medical News Today that the symptoms are no laughing matter: “People with recurrent UTI symptoms are sometimes desperate for something that helps them. I’ve had mums in tears over their kids’ UTIs, so having something they can try is a positive thing.”

According to study co-author Dr. Jacqueline Stephens, untreated UTIs can progress to the kidneys and to complications such as sepsis. She said that prevention is the best way to lower these risks.

Polyphenols: Cranberries’ power punch

Antibiotic prescriptions are the prevailing prevention and treatment protocol, which has contributed to the rise of medication-resistant pathogens.

Cranberry contains proanthocyanidins (PAC), a type of polyphenol. These “offense and defense” 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.”

An analysis of 50 studies

The researchers combed through the Cochrane Kidney and Transplant Specialized Register up to March 2023. They analyzed results from randomized 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.

Dr. Stephens shared:

“The studies we looked at included a range of methods to determine the benefits of cranberry products. The vast majority 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 following medical interventions such as bladder radiotherapy.”

Cranberry juice brings significant benefits

The study authors found that cranberry product consumption was strongly associated with a reduced risk of symptomatic, culture-verified UTIs in women with recurrent UTIs.

The researchers observed a significant protective benefit among children and individuals at risk of UTIs due to interventions such as 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. However, the study reported that the number of participants with these side effects “probably does not differ between those taking cranberry products and those receiving placebo or no specific treatment.”

Limited data

The research team noted that further studies are needed to determine which population with UTI would benefit the most from cranberry consumption.

Dr. Stephens cautioned that: “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. More data is required to be able to provide definitive advice about whether cranberry might be suitable for these groups of people.”

In an interview with MNT, Dr. Williams further noted: “In 2012, we had one trial in elderly people and this time we have three trials with 1,489 people. Our estimate suggests there may be a 7% slight reduction in risk […], but the precision is poor again, meaning we can’t be sure this estimate is right.”